Bob-Stanton wrote:
(Svante) wrote in message om...
Harmonic distorsion is expressed as the ratio between the distorsion
components and the fundamental. What surprises me is that it is the
VOLTAGES that are compared (in the electrical case) not the POWERS. So
if we have a second harmonic 40 dB down, the second harmonic
distorsion is 1 %, not 0.01 %.
(In this case the voltage of the harmonic is 1% of the fundamental,
and its power is 0.01% of the fundamental)

What is the reason for this convention? I'd think that power would be
more logical.

Using power is more valid. Power is used to express distortion,
outside of the audio industry. Distortion in other areas of
electronics is expressed in "dB's". For example, "the distortion is 20
dB down", means the distortion power is 0.01% of the signal power.



dB Power ratio Voltage


0 dB = 1 to 1 (of refrence power) 1.00 V (or ref. Voltage)
-10 dB = 1 to 0.1 0.316 V
-20 dB = 1 to 0.01 0.100 V
-30 dB = 1 to 0.001 0.031 V
-40 dB = 1 to 0.0001 0.010 V

In the audio community, voltage ratios are often expressed in dB, even
though it is not strictly valid to do so.

Audio has always been the rather backwards child of electronics.

You mean because no one uses transmssion line models to "study" speaker
cables? Only the truly backwards does that!

No, dB as a voltage ratio is just as valid as using dB as power ratio.
Given fixed impedance, a dB is a dB!

It's nothing to do with audio. It has everything to do with the fact
that for lower frequency electronics, it is often voltage gain and
current gain that is more important than power gain. For example, if you
have a circuit based on op-amps, the power gain means very little, since
there is such a huge mismatch between source and load impedances.
Voltage gain (and sometimes current gain, or transconductance and
transimpedance gain) is the standard way to express magnitude of
transfer functions, since the op amp behaves like a voltage source and
its gain does not depend on load. It has close to infinite power gain.

Similarly, if one designs integrated circuits, one seldom uses power
gains internally, since there is no transmission line effects to worry
about, and the impedance levels are not constant.

At high frequencies where transmission line effects are considered, dB's
are used both as voltage and power ratios, often interchangeably. There
is really no preference of one over the other. In fact, if you look at
your beloved s-parameters, they are standing wave ratios, of voltages!
S21, uusually expressed in dB and phase, is a voltage ratio.

I would however agree that high-end audio is the backwards child of
electronics.

John Fields wrote in message . ..
On 19 Jan 2004 00:59:29 -0800, (Svante)
wrote:


I think my reason is rather that i know that 20 dB is 10 times the
voltage and 100 times the power. Nice and even numbers. But I guess it
is like the americans still thinking in feet and inches.
So, in telecommunications, is there an example that the neper
simplifies things, compared to the decibel?

---
Do I perceive an attempt at America bashing/an insult/a flame??? Tsk,
tsk, tsk...

Don't take me too seriously on that, if you were insulted, my apologies.

John Fields wrote in message . ..
On 19 Jan 2004 00:59:29 -0800, (Svante)
wrote:


I think my reason is rather that i know that 20 dB is 10 times the
voltage and 100 times the power. Nice and even numbers. But I guess it
is like the americans still thinking in feet and inches.
So, in telecommunications, is there an example that the neper
simplifies things, compared to the decibel?

---
Do I perceive an attempt at America bashing/an insult/a flame??? Tsk,
tsk, tsk...

Don't take me too seriously on that, if you were insulted, my apologies.

John Fields wrote in message . ..
On 19 Jan 2004 00:59:29 -0800, (Svante)
wrote:


I think my reason is rather that i know that 20 dB is 10 times the
voltage and 100 times the power. Nice and even numbers. But I guess it
is like the americans still thinking in feet and inches.
So, in telecommunications, is there an example that the neper
simplifies things, compared to the decibel?

---
Do I perceive an attempt at America bashing/an insult/a flame??? Tsk,
tsk, tsk...

Don't take me too seriously on that, if you were insulted, my apologies.

John Fields wrote in message . ..
On 19 Jan 2004 00:59:29 -0800, (Svante)
wrote:


I think my reason is rather that i know that 20 dB is 10 times the
voltage and 100 times the power. Nice and even numbers. But I guess it
is like the americans still thinking in feet and inches.
So, in telecommunications, is there an example that the neper
simplifies things, compared to the decibel?

---
Do I perceive an attempt at America bashing/an insult/a flame??? Tsk,
tsk, tsk...

Don't take me too seriously on that, if you were insulted, my apologies.

On 20 Jan 2004 08:25:37 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).


Actually, no they don't (or, at least, not in the way you imply).
Sorry to burst that bubble Bob.
They use dB relatively (like the rest of us)

They use dBm's where the m implies 1 milliwatt.
Or they can use dBv's where v=.225V (again = 1mW in 50)
Both of those are specified powers into 50 Ohm load
which is the most commonly used environment for amps/test eq
and the usage is intended to specify a reference standard against which .....
An audio equiv is 0dBm (line level) of .775V in 600 Ohms = 1mW

This is the 'general' usage when 'those sorts of people' you mention
must specify 'absolute' reference levels. They would never "just" specify
dB's without defining the situation under which the level is being quoted.
To do otherwise is behaving like a car speaker salesperson (gotta be PC)

If they do just quote dB they are either ignorant, lazy or dishonest

On 20 Jan 2004 08:25:37 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).


Actually, no they don't (or, at least, not in the way you imply).
Sorry to burst that bubble Bob.
They use dB relatively (like the rest of us)

They use dBm's where the m implies 1 milliwatt.
Or they can use dBv's where v=.225V (again = 1mW in 50)
Both of those are specified powers into 50 Ohm load
which is the most commonly used environment for amps/test eq
and the usage is intended to specify a reference standard against which .....
An audio equiv is 0dBm (line level) of .775V in 600 Ohms = 1mW

This is the 'general' usage when 'those sorts of people' you mention
must specify 'absolute' reference levels. They would never "just" specify
dB's without defining the situation under which the level is being quoted.
To do otherwise is behaving like a car speaker salesperson (gotta be PC)

If they do just quote dB they are either ignorant, lazy or dishonest

On 20 Jan 2004 08:25:37 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).


Actually, no they don't (or, at least, not in the way you imply).
Sorry to burst that bubble Bob.
They use dB relatively (like the rest of us)

They use dBm's where the m implies 1 milliwatt.
Or they can use dBv's where v=.225V (again = 1mW in 50)
Both of those are specified powers into 50 Ohm load
which is the most commonly used environment for amps/test eq
and the usage is intended to specify a reference standard against which .....
An audio equiv is 0dBm (line level) of .775V in 600 Ohms = 1mW

This is the 'general' usage when 'those sorts of people' you mention
must specify 'absolute' reference levels. They would never "just" specify
dB's without defining the situation under which the level is being quoted.
To do otherwise is behaving like a car speaker salesperson (gotta be PC)

If they do just quote dB they are either ignorant, lazy or dishonest

On 20 Jan 2004 08:25:37 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).


Actually, no they don't (or, at least, not in the way you imply).
Sorry to burst that bubble Bob.
They use dB relatively (like the rest of us)

They use dBm's where the m implies 1 milliwatt.
Or they can use dBv's where v=.225V (again = 1mW in 50)
Both of those are specified powers into 50 Ohm load
which is the most commonly used environment for amps/test eq
and the usage is intended to specify a reference standard against which .....
An audio equiv is 0dBm (line level) of .775V in 600 Ohms = 1mW

This is the 'general' usage when 'those sorts of people' you mention
must specify 'absolute' reference levels. They would never "just" specify
dB's without defining the situation under which the level is being quoted.
To do otherwise is behaving like a car speaker salesperson (gotta be PC)

If they do just quote dB they are either ignorant, lazy or dishonest

Bazza wrote in message . ..
On 20 Jan 2004 08:25:37 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).


Actually, no they don't (or, at least, not in the way you imply).
Sorry to burst that bubble Bob.
They use dB relatively (like the rest of us)



I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.


They use dBm's where the m implies 1 milliwatt.

No, CATV companys don't use "dBm". That is a term that is common to
the military. CATV people uses "dBmV", which is 1 mV across 75 Ohms.

The term dBmV was invented by the Jerrold Co. in the 1950's, when the
Jerrold Company started the CATV industry. There was only 50 Ohm RF
test equipment at that time. The Jerrold company decided that they
would build their CATV systems with 75 Ohm cable. They had to design
their own 75 Ohm test equipment. One of the first things they designed
was a 75 Ohm Field Strength Meter.

Jerrod determined that the lowest signal level which would give a snow
free picture (to TV sets of the 1950's) was 1 mV. On their field
strength meter, they made the 0 dB scale equal to 1 mV. They called
the reference level "0 dbj". "j" stands for Jerrold. For a number of
years the CATV industry used the term "dBj". Latter, as other companys
got into manufacturing CATV equipment, they changed the term to
"dBmV".

Or they can use dBv's where v=.225V (again = 1mW in 50)
Both of those are specified powers into 50 Ohm load
which is the most commonly used environment for amps/test eq
and the usage is intended to specify a reference standard against which .....
An audio equiv is 0dBm (line level) of .775V in 600 Ohms = 1mW

This is the 'general' usage when 'those sorts of people' you mention
must specify 'absolute' reference levels. They would never "just" specify
dB's without defining the situation under which the level is being quoted.
To do otherwise is behaving like a car speaker salesperson (gotta be PC)


That is correct. Distortion is always a power level, relative to the
power of the signal. Or if you want to think of it this way: as a
voltage level, relative to the voltage of the signal.

If they do just quote dB they are either ignorant, lazy or dishonest

No no. Only audio people do that. :-)


Bob Stanton

Bazza wrote in message . ..
On 20 Jan 2004 08:25:37 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).


Actually, no they don't (or, at least, not in the way you imply).
Sorry to burst that bubble Bob.
They use dB relatively (like the rest of us)



I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.


They use dBm's where the m implies 1 milliwatt.

No, CATV companys don't use "dBm". That is a term that is common to
the military. CATV people uses "dBmV", which is 1 mV across 75 Ohms.

The term dBmV was invented by the Jerrold Co. in the 1950's, when the
Jerrold Company started the CATV industry. There was only 50 Ohm RF
test equipment at that time. The Jerrold company decided that they
would build their CATV systems with 75 Ohm cable. They had to design
their own 75 Ohm test equipment. One of the first things they designed
was a 75 Ohm Field Strength Meter.

Jerrod determined that the lowest signal level which would give a snow
free picture (to TV sets of the 1950's) was 1 mV. On their field
strength meter, they made the 0 dB scale equal to 1 mV. They called
the reference level "0 dbj". "j" stands for Jerrold. For a number of
years the CATV industry used the term "dBj". Latter, as other companys
got into manufacturing CATV equipment, they changed the term to
"dBmV".

Or they can use dBv's where v=.225V (again = 1mW in 50)
Both of those are specified powers into 50 Ohm load
which is the most commonly used environment for amps/test eq
and the usage is intended to specify a reference standard against which .....
An audio equiv is 0dBm (line level) of .775V in 600 Ohms = 1mW

This is the 'general' usage when 'those sorts of people' you mention
must specify 'absolute' reference levels. They would never "just" specify
dB's without defining the situation under which the level is being quoted.
To do otherwise is behaving like a car speaker salesperson (gotta be PC)


That is correct. Distortion is always a power level, relative to the
power of the signal. Or if you want to think of it this way: as a
voltage level, relative to the voltage of the signal.

If they do just quote dB they are either ignorant, lazy or dishonest

No no. Only audio people do that. :-)


Bob Stanton

Bazza wrote in message . ..
On 20 Jan 2004 08:25:37 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).


Actually, no they don't (or, at least, not in the way you imply).
Sorry to burst that bubble Bob.
They use dB relatively (like the rest of us)



I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.


They use dBm's where the m implies 1 milliwatt.

No, CATV companys don't use "dBm". That is a term that is common to
the military. CATV people uses "dBmV", which is 1 mV across 75 Ohms.

The term dBmV was invented by the Jerrold Co. in the 1950's, when the
Jerrold Company started the CATV industry. There was only 50 Ohm RF
test equipment at that time. The Jerrold company decided that they
would build their CATV systems with 75 Ohm cable. They had to design
their own 75 Ohm test equipment. One of the first things they designed
was a 75 Ohm Field Strength Meter.

Jerrod determined that the lowest signal level which would give a snow
free picture (to TV sets of the 1950's) was 1 mV. On their field
strength meter, they made the 0 dB scale equal to 1 mV. They called
the reference level "0 dbj". "j" stands for Jerrold. For a number of
years the CATV industry used the term "dBj". Latter, as other companys
got into manufacturing CATV equipment, they changed the term to
"dBmV".

Or they can use dBv's where v=.225V (again = 1mW in 50)
Both of those are specified powers into 50 Ohm load
which is the most commonly used environment for amps/test eq
and the usage is intended to specify a reference standard against which .....
An audio equiv is 0dBm (line level) of .775V in 600 Ohms = 1mW

This is the 'general' usage when 'those sorts of people' you mention
must specify 'absolute' reference levels. They would never "just" specify
dB's without defining the situation under which the level is being quoted.
To do otherwise is behaving like a car speaker salesperson (gotta be PC)


That is correct. Distortion is always a power level, relative to the
power of the signal. Or if you want to think of it this way: as a
voltage level, relative to the voltage of the signal.

If they do just quote dB they are either ignorant, lazy or dishonest

No no. Only audio people do that. :-)


Bob Stanton

Bazza wrote in message . ..
On 20 Jan 2004 08:25:37 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).


Actually, no they don't (or, at least, not in the way you imply).
Sorry to burst that bubble Bob.
They use dB relatively (like the rest of us)



I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.


They use dBm's where the m implies 1 milliwatt.

No, CATV companys don't use "dBm". That is a term that is common to
the military. CATV people uses "dBmV", which is 1 mV across 75 Ohms.

The term dBmV was invented by the Jerrold Co. in the 1950's, when the
Jerrold Company started the CATV industry. There was only 50 Ohm RF
test equipment at that time. The Jerrold company decided that they
would build their CATV systems with 75 Ohm cable. They had to design
their own 75 Ohm test equipment. One of the first things they designed
was a 75 Ohm Field Strength Meter.

Jerrod determined that the lowest signal level which would give a snow
free picture (to TV sets of the 1950's) was 1 mV. On their field
strength meter, they made the 0 dB scale equal to 1 mV. They called
the reference level "0 dbj". "j" stands for Jerrold. For a number of
years the CATV industry used the term "dBj". Latter, as other companys
got into manufacturing CATV equipment, they changed the term to
"dBmV".

Or they can use dBv's where v=.225V (again = 1mW in 50)
Both of those are specified powers into 50 Ohm load
which is the most commonly used environment for amps/test eq
and the usage is intended to specify a reference standard against which .....
An audio equiv is 0dBm (line level) of .775V in 600 Ohms = 1mW

This is the 'general' usage when 'those sorts of people' you mention
must specify 'absolute' reference levels. They would never "just" specify
dB's without defining the situation under which the level is being quoted.
To do otherwise is behaving like a car speaker salesperson (gotta be PC)


That is correct. Distortion is always a power level, relative to the
power of the signal. Or if you want to think of it this way: as a
voltage level, relative to the voltage of the signal.

If they do just quote dB they are either ignorant, lazy or dishonest

No no. Only audio people do that. :-)


Bob Stanton

On 21 Jan 2004 05:21:13 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.
However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?



They use dBm's where the m implies 1 milliwatt.

No, CATV companys don't use "dBm". That is a term that is common to
the military. CATV people uses "dBmV", which is 1 mV across 75 Ohms.

CATV's are outside my experience. Nor did I particularly single them out for
distinction. My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term and dBm's
when implying a 'standard' level. So, I'd contend that my statement holds true

The term dBmV was invented by the Jerrold Co. in the 1950's, when the
Jerrold Company started the CATV industry. There was only 50 Ohm RF
test equipment at that time. The Jerrold company decided that they
would build their CATV systems with 75 Ohm cable. They had to design
their own 75 Ohm test equipment. One of the first things they designed
was a 75 Ohm Field Strength Meter.

Again. You may be right with regard to CATV systems and tho' its an
interesting slice of history I'd still say with/without its possible formative
influence, that modern usage (i.e. dBm) is as I pointed out in the previous
post. There's also the possibility that I really do mean dBmv but I got
mentally lazy myself over the years and habitually dropped off the 'v' bit -)

But , aaaagh, there were 75 Ohm cable systems and deliberately designed
signal generators / measurement systems back in the 'good ol days'.
And a pain it was too.


Jerrod determined that the lowest signal level which would give a snow
free picture (to TV sets of the 1950's) was 1 mV. On their field
strength meter, they made the 0 dB scale equal to 1 mV. They called
the reference level "0 dbj". "j" stands for Jerrold. For a number of
years the CATV industry used the term "dBj". Latter, as other companys
got into manufacturing CATV equipment, they changed the term to
"dBmV".

Interesting, but, having been in this industry since 1959, DBmv has not had a
lot of impact in a commonly used sense. Everything, and I'm referring to dB's
when defining particular power levels, was in dBm's or dBv's with a quoted Z.

If they do just quote dB they are either ignorant, lazy or dishonest
No no. Only audio people do that. :-)

Heh

On 21 Jan 2004 05:21:13 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.
However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?



They use dBm's where the m implies 1 milliwatt.

No, CATV companys don't use "dBm". That is a term that is common to
the military. CATV people uses "dBmV", which is 1 mV across 75 Ohms.

CATV's are outside my experience. Nor did I particularly single them out for
distinction. My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term and dBm's
when implying a 'standard' level. So, I'd contend that my statement holds true

The term dBmV was invented by the Jerrold Co. in the 1950's, when the
Jerrold Company started the CATV industry. There was only 50 Ohm RF
test equipment at that time. The Jerrold company decided that they
would build their CATV systems with 75 Ohm cable. They had to design
their own 75 Ohm test equipment. One of the first things they designed
was a 75 Ohm Field Strength Meter.

Again. You may be right with regard to CATV systems and tho' its an
interesting slice of history I'd still say with/without its possible formative
influence, that modern usage (i.e. dBm) is as I pointed out in the previous
post. There's also the possibility that I really do mean dBmv but I got
mentally lazy myself over the years and habitually dropped off the 'v' bit -)

But , aaaagh, there were 75 Ohm cable systems and deliberately designed
signal generators / measurement systems back in the 'good ol days'.
And a pain it was too.


Jerrod determined that the lowest signal level which would give a snow
free picture (to TV sets of the 1950's) was 1 mV. On their field
strength meter, they made the 0 dB scale equal to 1 mV. They called
the reference level "0 dbj". "j" stands for Jerrold. For a number of
years the CATV industry used the term "dBj". Latter, as other companys
got into manufacturing CATV equipment, they changed the term to
"dBmV".

Interesting, but, having been in this industry since 1959, DBmv has not had a
lot of impact in a commonly used sense. Everything, and I'm referring to dB's
when defining particular power levels, was in dBm's or dBv's with a quoted Z.

If they do just quote dB they are either ignorant, lazy or dishonest
No no. Only audio people do that. :-)

Heh

On 21 Jan 2004 05:21:13 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.
However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?



They use dBm's where the m implies 1 milliwatt.

No, CATV companys don't use "dBm". That is a term that is common to
the military. CATV people uses "dBmV", which is 1 mV across 75 Ohms.

CATV's are outside my experience. Nor did I particularly single them out for
distinction. My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term and dBm's
when implying a 'standard' level. So, I'd contend that my statement holds true

The term dBmV was invented by the Jerrold Co. in the 1950's, when the
Jerrold Company started the CATV industry. There was only 50 Ohm RF
test equipment at that time. The Jerrold company decided that they
would build their CATV systems with 75 Ohm cable. They had to design
their own 75 Ohm test equipment. One of the first things they designed
was a 75 Ohm Field Strength Meter.

Again. You may be right with regard to CATV systems and tho' its an
interesting slice of history I'd still say with/without its possible formative
influence, that modern usage (i.e. dBm) is as I pointed out in the previous
post. There's also the possibility that I really do mean dBmv but I got
mentally lazy myself over the years and habitually dropped off the 'v' bit -)

But , aaaagh, there were 75 Ohm cable systems and deliberately designed
signal generators / measurement systems back in the 'good ol days'.
And a pain it was too.


Jerrod determined that the lowest signal level which would give a snow
free picture (to TV sets of the 1950's) was 1 mV. On their field
strength meter, they made the 0 dB scale equal to 1 mV. They called
the reference level "0 dbj". "j" stands for Jerrold. For a number of
years the CATV industry used the term "dBj". Latter, as other companys
got into manufacturing CATV equipment, they changed the term to
"dBmV".

Interesting, but, having been in this industry since 1959, DBmv has not had a
lot of impact in a commonly used sense. Everything, and I'm referring to dB's
when defining particular power levels, was in dBm's or dBv's with a quoted Z.

If they do just quote dB they are either ignorant, lazy or dishonest
No no. Only audio people do that. :-)

Heh

On 21 Jan 2004 05:21:13 -0800, (Bob-Stanton) wrote:

Makers of RF amplifiers, and fiber optic equipment. All makers of CATV
and fiber optic equipment specify broadband distortion in -dB (power).
Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.
However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?



They use dBm's where the m implies 1 milliwatt.

No, CATV companys don't use "dBm". That is a term that is common to
the military. CATV people uses "dBmV", which is 1 mV across 75 Ohms.

CATV's are outside my experience. Nor did I particularly single them out for
distinction. My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term and dBm's
when implying a 'standard' level. So, I'd contend that my statement holds true

The term dBmV was invented by the Jerrold Co. in the 1950's, when the
Jerrold Company started the CATV industry. There was only 50 Ohm RF
test equipment at that time. The Jerrold company decided that they
would build their CATV systems with 75 Ohm cable. They had to design
their own 75 Ohm test equipment. One of the first things they designed
was a 75 Ohm Field Strength Meter.

Again. You may be right with regard to CATV systems and tho' its an
interesting slice of history I'd still say with/without its possible formative
influence, that modern usage (i.e. dBm) is as I pointed out in the previous
post. There's also the possibility that I really do mean dBmv but I got
mentally lazy myself over the years and habitually dropped off the 'v' bit -)

But , aaaagh, there were 75 Ohm cable systems and deliberately designed
signal generators / measurement systems back in the 'good ol days'.
And a pain it was too.


Jerrod determined that the lowest signal level which would give a snow
free picture (to TV sets of the 1950's) was 1 mV. On their field
strength meter, they made the 0 dB scale equal to 1 mV. They called
the reference level "0 dbj". "j" stands for Jerrold. For a number of
years the CATV industry used the term "dBj". Latter, as other companys
got into manufacturing CATV equipment, they changed the term to
"dBmV".

Interesting, but, having been in this industry since 1959, DBmv has not had a
lot of impact in a commonly used sense. Everything, and I'm referring to dB's
when defining particular power levels, was in dBm's or dBv's with a quoted Z.

If they do just quote dB they are either ignorant, lazy or dishonest
No no. Only audio people do that. :-)

Heh

On 17 Jan 2004 08:40:54 -0800, (Svante)
wrote:

(Stewart Pinkerton) wrote in message ...
On 17 Jan 2004 02:02:57 -0800, (Svante)
wrote:

However, this would actually speak against
using dB as a measure of distorsion, since dB is fundamentally
intended to measure a POWER ratio.

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

Nope. Think a bit. "deci" is a tenth. Why would mister Bell have
defined a Bel as TWO times the logarithm of the ratio between two
voltages/pressures/currents?

He didn't, he defined it as the ratio of two sound pressures which
aree perceived as a doubling of loudness. Everything else is
derivative, and a consequence of the logarithmic response of our ears.
BTW, as Dick Pierce pointed out, a sound pressure level is
proportional to a power measure, so not equivalent to voltage or
current.

So I guess it is safe to assume that the fundament of the deciBel
rests on a power ratio.

No, that's a derivative of the original definition, as is the voltage
derivative.

3. The measuring equipment measures ratios of voltages. It does not
measure power delivered to the load.

So... A spectral display based on voltage measurement should not
really be allowed to display "dB" on the y axis, unless we know that
we have a constant, resistive load?

Not at all, since a voltage ratio of 2:1 is approximately 6dB,
regardless of current flow. This is why voltage, not power, is used
as a standard measure of speaker sensitivity, since it is independent
of the load impedance.

Not if the decibel indicates the power ratio.

It doesn't so, why are you persisting in this dogged determination to
argue against the International Standards Organisation?

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance. It simply assumes that the load
resistenace is constant.

It assumes no such thing.

If you get back to the fundaments, it does.

No, if you get back to the fundamantals, it has nothing to do with
electricity at all.

I am just trying to point out that on the way to the voltage ratio,
somewhere, the resistance has been ignored.

No, it hasn't.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 17 Jan 2004 08:40:54 -0800, (Svante)
wrote:

(Stewart Pinkerton) wrote in message ...
On 17 Jan 2004 02:02:57 -0800, (Svante)
wrote:

However, this would actually speak against
using dB as a measure of distorsion, since dB is fundamentally
intended to measure a POWER ratio.

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

Nope. Think a bit. "deci" is a tenth. Why would mister Bell have
defined a Bel as TWO times the logarithm of the ratio between two
voltages/pressures/currents?

He didn't, he defined it as the ratio of two sound pressures which
aree perceived as a doubling of loudness. Everything else is
derivative, and a consequence of the logarithmic response of our ears.
BTW, as Dick Pierce pointed out, a sound pressure level is
proportional to a power measure, so not equivalent to voltage or
current.

So I guess it is safe to assume that the fundament of the deciBel
rests on a power ratio.

No, that's a derivative of the original definition, as is the voltage
derivative.

3. The measuring equipment measures ratios of voltages. It does not
measure power delivered to the load.

So... A spectral display based on voltage measurement should not
really be allowed to display "dB" on the y axis, unless we know that
we have a constant, resistive load?

Not at all, since a voltage ratio of 2:1 is approximately 6dB,
regardless of current flow. This is why voltage, not power, is used
as a standard measure of speaker sensitivity, since it is independent
of the load impedance.

Not if the decibel indicates the power ratio.

It doesn't so, why are you persisting in this dogged determination to
argue against the International Standards Organisation?

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance. It simply assumes that the load
resistenace is constant.

It assumes no such thing.

If you get back to the fundaments, it does.

No, if you get back to the fundamantals, it has nothing to do with
electricity at all.

I am just trying to point out that on the way to the voltage ratio,
somewhere, the resistance has been ignored.

No, it hasn't.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 17 Jan 2004 08:40:54 -0800, (Svante)
wrote:

(Stewart Pinkerton) wrote in message ...
On 17 Jan 2004 02:02:57 -0800, (Svante)
wrote:

However, this would actually speak against
using dB as a measure of distorsion, since dB is fundamentally
intended to measure a POWER ratio.

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

Nope. Think a bit. "deci" is a tenth. Why would mister Bell have
defined a Bel as TWO times the logarithm of the ratio between two
voltages/pressures/currents?

He didn't, he defined it as the ratio of two sound pressures which
aree perceived as a doubling of loudness. Everything else is
derivative, and a consequence of the logarithmic response of our ears.
BTW, as Dick Pierce pointed out, a sound pressure level is
proportional to a power measure, so not equivalent to voltage or
current.

So I guess it is safe to assume that the fundament of the deciBel
rests on a power ratio.

No, that's a derivative of the original definition, as is the voltage
derivative.

3. The measuring equipment measures ratios of voltages. It does not
measure power delivered to the load.

So... A spectral display based on voltage measurement should not
really be allowed to display "dB" on the y axis, unless we know that
we have a constant, resistive load?

Not at all, since a voltage ratio of 2:1 is approximately 6dB,
regardless of current flow. This is why voltage, not power, is used
as a standard measure of speaker sensitivity, since it is independent
of the load impedance.

Not if the decibel indicates the power ratio.

It doesn't so, why are you persisting in this dogged determination to
argue against the International Standards Organisation?

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance. It simply assumes that the load
resistenace is constant.

It assumes no such thing.

If you get back to the fundaments, it does.

No, if you get back to the fundamantals, it has nothing to do with
electricity at all.

I am just trying to point out that on the way to the voltage ratio,
somewhere, the resistance has been ignored.

No, it hasn't.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On 17 Jan 2004 08:40:54 -0800, (Svante)
wrote:

(Stewart Pinkerton) wrote in message ...
On 17 Jan 2004 02:02:57 -0800, (Svante)
wrote:

However, this would actually speak against
using dB as a measure of distorsion, since dB is fundamentally
intended to measure a POWER ratio.

The dB was originally a measure of sound pressure level, and the
logarithmic scale is used simply becuause our ears respond to sound in
a logarithmic fashion.

Nope. Think a bit. "deci" is a tenth. Why would mister Bell have
defined a Bel as TWO times the logarithm of the ratio between two
voltages/pressures/currents?

He didn't, he defined it as the ratio of two sound pressures which
aree perceived as a doubling of loudness. Everything else is
derivative, and a consequence of the logarithmic response of our ears.
BTW, as Dick Pierce pointed out, a sound pressure level is
proportional to a power measure, so not equivalent to voltage or
current.

So I guess it is safe to assume that the fundament of the deciBel
rests on a power ratio.

No, that's a derivative of the original definition, as is the voltage
derivative.

3. The measuring equipment measures ratios of voltages. It does not
measure power delivered to the load.

So... A spectral display based on voltage measurement should not
really be allowed to display "dB" on the y axis, unless we know that
we have a constant, resistive load?

Not at all, since a voltage ratio of 2:1 is approximately 6dB,
regardless of current flow. This is why voltage, not power, is used
as a standard measure of speaker sensitivity, since it is independent
of the load impedance.

Not if the decibel indicates the power ratio.

It doesn't so, why are you persisting in this dogged determination to
argue against the International Standards Organisation?

The equation for "voltage dBs"
(20*log(u/uref)) is a derivation based on that p~u^2 neglecting the
effects of varying load resistance. It simply assumes that the load
resistenace is constant.

It assumes no such thing.

If you get back to the fundaments, it does.

No, if you get back to the fundamantals, it has nothing to do with
electricity at all.

I am just trying to point out that on the way to the voltage ratio,
somewhere, the resistance has been ignored.

No, it hasn't.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Bazza wrote in message



Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.

Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Filters *can not* be used to reduce the *inband distoriton*, of
broadband amplifiers. Suppose a broadband amplifier was carrying fifty
TV channels. It will have some 2nd order and 3rd order distortion. One
form of 3rd order distortion is cross modulation. How could a filter
be used to "filter" out crossmodulation? The answer is: it couldn't.


However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?


My statement is simple. Perhaps you don't understand it, because you
are looking for something too complex.

Distortion level is always relative to the signal level. It makes no
difference what the absolute values are.

If an amplifier is putting out a 1.0 v signal, and the distortion is
0.1 V, than the distortion is -20 dB. If an amplifier is putting out
10.0 V of signal, and the distortion is 1.0 V than the distortion is
-20 dB. It makes no difference what the absolute levels are.




My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term

Yes, we agreed on this, can we go on to something else?




... and dBm's when implying a 'standard' level. So, I'd contend that my
statement holds true


Companys use "dBmV" for 75 Ohm equipment, and "dBm" for the 50 Ohm
equipment. So, there are two 'standard' levels.



But , aaaagh, there were 75 Ohm cable systems and deliberately designed
signal generators / measurement systems back in the 'good ol days'.
And a pain it was too.

I agree. The "good ol days" were not that good. Can you imagine the
difficulty in starting a new industry, to sell electronic products,
for which there was no test equipment?




....they changed the term to"dBmV".

Interesting, but, having been in this industry since 1959, DBmv has not had a
lot of impact in a commonly used sense.

Having been involved in the CATV field since 1958, I can tell you that
"dBj" was and still is, the *only* reference level used for 75 Ohm
equipment. "dBj" may not have been a common term where you worked, but
CATV was not even known about, by many people, back in 1959.

Bob Stanton

Bazza wrote in message



Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.

Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Filters *can not* be used to reduce the *inband distoriton*, of
broadband amplifiers. Suppose a broadband amplifier was carrying fifty
TV channels. It will have some 2nd order and 3rd order distortion. One
form of 3rd order distortion is cross modulation. How could a filter
be used to "filter" out crossmodulation? The answer is: it couldn't.


However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?


My statement is simple. Perhaps you don't understand it, because you
are looking for something too complex.

Distortion level is always relative to the signal level. It makes no
difference what the absolute values are.

If an amplifier is putting out a 1.0 v signal, and the distortion is
0.1 V, than the distortion is -20 dB. If an amplifier is putting out
10.0 V of signal, and the distortion is 1.0 V than the distortion is
-20 dB. It makes no difference what the absolute levels are.




My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term

Yes, we agreed on this, can we go on to something else?




... and dBm's when implying a 'standard' level. So, I'd contend that my
statement holds true


Companys use "dBmV" for 75 Ohm equipment, and "dBm" for the 50 Ohm
equipment. So, there are two 'standard' levels.



But , aaaagh, there were 75 Ohm cable systems and deliberately designed
signal generators / measurement systems back in the 'good ol days'.
And a pain it was too.

I agree. The "good ol days" were not that good. Can you imagine the
difficulty in starting a new industry, to sell electronic products,
for which there was no test equipment?




....they changed the term to"dBmV".

Interesting, but, having been in this industry since 1959, DBmv has not had a
lot of impact in a commonly used sense.

Having been involved in the CATV field since 1958, I can tell you that
"dBj" was and still is, the *only* reference level used for 75 Ohm
equipment. "dBj" may not have been a common term where you worked, but
CATV was not even known about, by many people, back in 1959.

Bob Stanton

Bazza wrote in message



Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.

Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Filters *can not* be used to reduce the *inband distoriton*, of
broadband amplifiers. Suppose a broadband amplifier was carrying fifty
TV channels. It will have some 2nd order and 3rd order distortion. One
form of 3rd order distortion is cross modulation. How could a filter
be used to "filter" out crossmodulation? The answer is: it couldn't.


However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?


My statement is simple. Perhaps you don't understand it, because you
are looking for something too complex.

Distortion level is always relative to the signal level. It makes no
difference what the absolute values are.

If an amplifier is putting out a 1.0 v signal, and the distortion is
0.1 V, than the distortion is -20 dB. If an amplifier is putting out
10.0 V of signal, and the distortion is 1.0 V than the distortion is
-20 dB. It makes no difference what the absolute levels are.




My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term

Yes, we agreed on this, can we go on to something else?




... and dBm's when implying a 'standard' level. So, I'd contend that my
statement holds true


Companys use "dBmV" for 75 Ohm equipment, and "dBm" for the 50 Ohm
equipment. So, there are two 'standard' levels.



But , aaaagh, there were 75 Ohm cable systems and deliberately designed
signal generators / measurement systems back in the 'good ol days'.
And a pain it was too.

I agree. The "good ol days" were not that good. Can you imagine the
difficulty in starting a new industry, to sell electronic products,
for which there was no test equipment?




....they changed the term to"dBmV".

Interesting, but, having been in this industry since 1959, DBmv has not had a
lot of impact in a commonly used sense.

Having been involved in the CATV field since 1958, I can tell you that
"dBj" was and still is, the *only* reference level used for 75 Ohm
equipment. "dBj" may not have been a common term where you worked, but
CATV was not even known about, by many people, back in 1959.

Bob Stanton

Bazza wrote in message



Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.

Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Filters *can not* be used to reduce the *inband distoriton*, of
broadband amplifiers. Suppose a broadband amplifier was carrying fifty
TV channels. It will have some 2nd order and 3rd order distortion. One
form of 3rd order distortion is cross modulation. How could a filter
be used to "filter" out crossmodulation? The answer is: it couldn't.


However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?


My statement is simple. Perhaps you don't understand it, because you
are looking for something too complex.

Distortion level is always relative to the signal level. It makes no
difference what the absolute values are.

If an amplifier is putting out a 1.0 v signal, and the distortion is
0.1 V, than the distortion is -20 dB. If an amplifier is putting out
10.0 V of signal, and the distortion is 1.0 V than the distortion is
-20 dB. It makes no difference what the absolute levels are.




My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term

Yes, we agreed on this, can we go on to something else?




... and dBm's when implying a 'standard' level. So, I'd contend that my
statement holds true


Companys use "dBmV" for 75 Ohm equipment, and "dBm" for the 50 Ohm
equipment. So, there are two 'standard' levels.



But , aaaagh, there were 75 Ohm cable systems and deliberately designed
signal generators / measurement systems back in the 'good ol days'.
And a pain it was too.

I agree. The "good ol days" were not that good. Can you imagine the
difficulty in starting a new industry, to sell electronic products,
for which there was no test equipment?




....they changed the term to"dBmV".

Interesting, but, having been in this industry since 1959, DBmv has not had a
lot of impact in a commonly used sense.

Having been involved in the CATV field since 1958, I can tell you that
"dBj" was and still is, the *only* reference level used for 75 Ohm
equipment. "dBj" may not have been a common term where you worked, but
CATV was not even known about, by many people, back in 1959.

Bob Stanton

On 22 Jan 2004 04:30:23 -0800, (Bob-Stanton) wrote:

Bazza wrote in message



Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.


No, Bob. I disagree. I am considering and restricting myself to pretty much
ONLY RF engineering in its broadest context of transmitters and band systems.
I'd go a bit further and say that although CATV is ubiquitous it's not the
"raison d'etre" for an RF engineers life -(. True, you could make a case for
very wide band situations perhaps such as CATV but this implies an agreed
definition of what constitutes a wide band and, as I admitted before, I cannot
speak for CATV situations. I will say this tho'. No matter what the 'in-house'
measurement system is for that discipline, ultimately you'll end up referring
it to those "good-ol'-time" - frequency / power. Which of course is where I
entered this dB fest -)


Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Did'nt say THEY wern't ( did I?). Don't think I did anyway. But if I had, it
was in the context of relating it to the audio type of discussion that was
going on in here. (And yes, I do know about mixing etc). As far as in-band -
there's no argument from me about that.


Filters *can not* be used to reduce the *inband distoriton*, of
broadband amplifiers. Suppose a broadband amplifier was carrying fifty
TV channels. It will have some 2nd order and 3rd order distortion. One
form of 3rd order distortion is cross modulation. How could a filter
be used to "filter" out crossmodulation? The answer is: it couldn't.

I did not say that they were used (in-band). I mentioned them and thinking, at
the same time of RF signal generators / RF amps - all of which should have low
spectral impurity e.g. second / third harmonics. In those situations filters
are effective. (and absolutely requisite in some instances)



However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?


My statement is simple. Perhaps you don't understand it, because you
are looking for something too complex.

Not necessarily. It merely means I did not understand what you were getting
at. Quite often things are clear in our minds when we write but due to to
cultural differences or terminology habits, there can be some momentary
interruption to the cross flow of understanding.



Distortion level is always relative to the signal level. It makes no
difference what the absolute values are.

If an amplifier is putting out a 1.0 v signal, and the distortion is
0.1 V, than the distortion is -20 dB. If an amplifier is putting out
10.0 V of signal, and the distortion is 1.0 V than the distortion is
-20 dB. It makes no difference what the absolute levels are.

Yes. Agreed.

My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term

Yes, we agreed on this, can we go on to something else?

Silly me. I thought we had.


... and dBm's when implying a 'standard' level. So, I'd contend that my
statement holds true
Companys use "dBmV" for 75 Ohm equipment, and "dBm" for the 50 Ohm
equipment. So, there are two 'standard' levels.

That's OK.
I appreciate the descriptive difference now.
I had to work with both as well.


[Rest snipped]

Similar vintage
(relatively speaking) -)

On 22 Jan 2004 04:30:23 -0800, (Bob-Stanton) wrote:

Bazza wrote in message



Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.


No, Bob. I disagree. I am considering and restricting myself to pretty much
ONLY RF engineering in its broadest context of transmitters and band systems.
I'd go a bit further and say that although CATV is ubiquitous it's not the
"raison d'etre" for an RF engineers life -(. True, you could make a case for
very wide band situations perhaps such as CATV but this implies an agreed
definition of what constitutes a wide band and, as I admitted before, I cannot
speak for CATV situations. I will say this tho'. No matter what the 'in-house'
measurement system is for that discipline, ultimately you'll end up referring
it to those "good-ol'-time" - frequency / power. Which of course is where I
entered this dB fest -)


Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Did'nt say THEY wern't ( did I?). Don't think I did anyway. But if I had, it
was in the context of relating it to the audio type of discussion that was
going on in here. (And yes, I do know about mixing etc). As far as in-band -
there's no argument from me about that.


Filters *can not* be used to reduce the *inband distoriton*, of
broadband amplifiers. Suppose a broadband amplifier was carrying fifty
TV channels. It will have some 2nd order and 3rd order distortion. One
form of 3rd order distortion is cross modulation. How could a filter
be used to "filter" out crossmodulation? The answer is: it couldn't.

I did not say that they were used (in-band). I mentioned them and thinking, at
the same time of RF signal generators / RF amps - all of which should have low
spectral impurity e.g. second / third harmonics. In those situations filters
are effective. (and absolutely requisite in some instances)



However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?


My statement is simple. Perhaps you don't understand it, because you
are looking for something too complex.

Not necessarily. It merely means I did not understand what you were getting
at. Quite often things are clear in our minds when we write but due to to
cultural differences or terminology habits, there can be some momentary
interruption to the cross flow of understanding.



Distortion level is always relative to the signal level. It makes no
difference what the absolute values are.

If an amplifier is putting out a 1.0 v signal, and the distortion is
0.1 V, than the distortion is -20 dB. If an amplifier is putting out
10.0 V of signal, and the distortion is 1.0 V than the distortion is
-20 dB. It makes no difference what the absolute levels are.

Yes. Agreed.

My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term

Yes, we agreed on this, can we go on to something else?

Silly me. I thought we had.


... and dBm's when implying a 'standard' level. So, I'd contend that my
statement holds true
Companys use "dBmV" for 75 Ohm equipment, and "dBm" for the 50 Ohm
equipment. So, there are two 'standard' levels.

That's OK.
I appreciate the descriptive difference now.
I had to work with both as well.


[Rest snipped]

Similar vintage
(relatively speaking) -)

On 22 Jan 2004 04:30:23 -0800, (Bob-Stanton) wrote:

Bazza wrote in message



Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.


No, Bob. I disagree. I am considering and restricting myself to pretty much
ONLY RF engineering in its broadest context of transmitters and band systems.
I'd go a bit further and say that although CATV is ubiquitous it's not the
"raison d'etre" for an RF engineers life -(. True, you could make a case for
very wide band situations perhaps such as CATV but this implies an agreed
definition of what constitutes a wide band and, as I admitted before, I cannot
speak for CATV situations. I will say this tho'. No matter what the 'in-house'
measurement system is for that discipline, ultimately you'll end up referring
it to those "good-ol'-time" - frequency / power. Which of course is where I
entered this dB fest -)


Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Did'nt say THEY wern't ( did I?). Don't think I did anyway. But if I had, it
was in the context of relating it to the audio type of discussion that was
going on in here. (And yes, I do know about mixing etc). As far as in-band -
there's no argument from me about that.


Filters *can not* be used to reduce the *inband distoriton*, of
broadband amplifiers. Suppose a broadband amplifier was carrying fifty
TV channels. It will have some 2nd order and 3rd order distortion. One
form of 3rd order distortion is cross modulation. How could a filter
be used to "filter" out crossmodulation? The answer is: it couldn't.

I did not say that they were used (in-band). I mentioned them and thinking, at
the same time of RF signal generators / RF amps - all of which should have low
spectral impurity e.g. second / third harmonics. In those situations filters
are effective. (and absolutely requisite in some instances)



However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?


My statement is simple. Perhaps you don't understand it, because you
are looking for something too complex.

Not necessarily. It merely means I did not understand what you were getting
at. Quite often things are clear in our minds when we write but due to to
cultural differences or terminology habits, there can be some momentary
interruption to the cross flow of understanding.



Distortion level is always relative to the signal level. It makes no
difference what the absolute values are.

If an amplifier is putting out a 1.0 v signal, and the distortion is
0.1 V, than the distortion is -20 dB. If an amplifier is putting out
10.0 V of signal, and the distortion is 1.0 V than the distortion is
-20 dB. It makes no difference what the absolute levels are.

Yes. Agreed.

My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term

Yes, we agreed on this, can we go on to something else?

Silly me. I thought we had.


... and dBm's when implying a 'standard' level. So, I'd contend that my
statement holds true
Companys use "dBmV" for 75 Ohm equipment, and "dBm" for the 50 Ohm
equipment. So, there are two 'standard' levels.

That's OK.
I appreciate the descriptive difference now.
I had to work with both as well.


[Rest snipped]

Similar vintage
(relatively speaking) -)

On 22 Jan 2004 04:30:23 -0800, (Bob-Stanton) wrote:

Bazza wrote in message



Companys like: General Instrument, Scientific Atlanta, C-Cor, and
Philips(Magnavox).

Generally, those applications are not interested in DISTORTION as such.
A bandpass filter could be used to reduce out of band signals, sometimes
lowpass, even less frequently, highpass. This would be especially the case for
RF amplifiers, broadband RF amps and to some extent transmitters etc.


No, Bob. I disagree. I am considering and restricting myself to pretty much
ONLY RF engineering in its broadest context of transmitters and band systems.
I'd go a bit further and say that although CATV is ubiquitous it's not the
"raison d'etre" for an RF engineers life -(. True, you could make a case for
very wide band situations perhaps such as CATV but this implies an agreed
definition of what constitutes a wide band and, as I admitted before, I cannot
speak for CATV situations. I will say this tho'. No matter what the 'in-house'
measurement system is for that discipline, ultimately you'll end up referring
it to those "good-ol'-time" - frequency / power. Which of course is where I
entered this dB fest -)


Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Did'nt say THEY wern't ( did I?). Don't think I did anyway. But if I had, it
was in the context of relating it to the audio type of discussion that was
going on in here. (And yes, I do know about mixing etc). As far as in-band -
there's no argument from me about that.


Filters *can not* be used to reduce the *inband distoriton*, of
broadband amplifiers. Suppose a broadband amplifier was carrying fifty
TV channels. It will have some 2nd order and 3rd order distortion. One
form of 3rd order distortion is cross modulation. How could a filter
be used to "filter" out crossmodulation? The answer is: it couldn't.

I did not say that they were used (in-band). I mentioned them and thinking, at
the same time of RF signal generators / RF amps - all of which should have low
spectral impurity e.g. second / third harmonics. In those situations filters
are effective. (and absolutely requisite in some instances)



However, we are biginning to stray from the original post. It was your
second-line statement, above, to which I was makeing an exception

I agree. They use dB as a relative level, when it comes to specifying
distortion. When I wrote "distortion in -dB(power)", I ment the
distortion power *relative* to the signal power.
Eh ?


My statement is simple. Perhaps you don't understand it, because you
are looking for something too complex.

Not necessarily. It merely means I did not understand what you were getting
at. Quite often things are clear in our minds when we write but due to to
cultural differences or terminology habits, there can be some momentary
interruption to the cross flow of understanding.



Distortion level is always relative to the signal level. It makes no
difference what the absolute values are.

If an amplifier is putting out a 1.0 v signal, and the distortion is
0.1 V, than the distortion is -20 dB. If an amplifier is putting out
10.0 V of signal, and the distortion is 1.0 V than the distortion is
-20 dB. It makes no difference what the absolute levels are.

Yes. Agreed.

My point was that most people in the side industries (non-audio)
which you cited, still use and properly so, dB's as a relative term

Yes, we agreed on this, can we go on to something else?

Silly me. I thought we had.


... and dBm's when implying a 'standard' level. So, I'd contend that my
statement holds true
Companys use "dBmV" for 75 Ohm equipment, and "dBm" for the 50 Ohm
equipment. So, there are two 'standard' levels.

That's OK.
I appreciate the descriptive difference now.
I had to work with both as well.


[Rest snipped]

Similar vintage
(relatively speaking) -)

Bazza wrote in message


No, Bob. I disagree. I am considering and restricting myself to pretty much
ONLY RF engineering in its broadest context of transmitters and band systems.
I'd go a bit further and say that although CATV is ubiquitous it's not the
"raison d'etre" for an RF engineers life -(. True, you could make a case for
very wide band situations perhaps such as CATV but this implies an agreed
definition of what constitutes a wide band and, as I admitted before, I cannot
speak for CATV situations. I will say this tho'. No matter what the 'in-house'
measurement system is for that discipline, ultimately you'll end up referring
it to those "good-ol'-time" - frequency / power. Which of course is where I
entered this dB fest -)


Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Did'nt say THEY wern't ( did I?). Don't think I did anyway. But if I had, it
was in the context of relating it to the audio type of discussion that was
going on in here. (And yes, I do know about mixing etc). As far as in-band -
there's no argument from me about that.



I did not say that they were used (in-band). I mentioned them and thinking, at
the same time of RF signal generators / RF amps - all of which should have low
spectral impurity e.g. second / third harmonics. In those situations filters
are effective. (and absolutely requisite in some instances)


Not necessarily. It merely means I did not understand what you were getting
at. Quite often things are clear in our minds when we write but due to to
cultural differences or terminology habits, there can be some momentary
interruption to the cross flow of understanding.



I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)

Bob Stanton

Bazza wrote in message


No, Bob. I disagree. I am considering and restricting myself to pretty much
ONLY RF engineering in its broadest context of transmitters and band systems.
I'd go a bit further and say that although CATV is ubiquitous it's not the
"raison d'etre" for an RF engineers life -(. True, you could make a case for
very wide band situations perhaps such as CATV but this implies an agreed
definition of what constitutes a wide band and, as I admitted before, I cannot
speak for CATV situations. I will say this tho'. No matter what the 'in-house'
measurement system is for that discipline, ultimately you'll end up referring
it to those "good-ol'-time" - frequency / power. Which of course is where I
entered this dB fest -)


Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Did'nt say THEY wern't ( did I?). Don't think I did anyway. But if I had, it
was in the context of relating it to the audio type of discussion that was
going on in here. (And yes, I do know about mixing etc). As far as in-band -
there's no argument from me about that.



I did not say that they were used (in-band). I mentioned them and thinking, at
the same time of RF signal generators / RF amps - all of which should have low
spectral impurity e.g. second / third harmonics. In those situations filters
are effective. (and absolutely requisite in some instances)


Not necessarily. It merely means I did not understand what you were getting
at. Quite often things are clear in our minds when we write but due to to
cultural differences or terminology habits, there can be some momentary
interruption to the cross flow of understanding.



I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)

Bob Stanton

Bazza wrote in message


No, Bob. I disagree. I am considering and restricting myself to pretty much
ONLY RF engineering in its broadest context of transmitters and band systems.
I'd go a bit further and say that although CATV is ubiquitous it's not the
"raison d'etre" for an RF engineers life -(. True, you could make a case for
very wide band situations perhaps such as CATV but this implies an agreed
definition of what constitutes a wide band and, as I admitted before, I cannot
speak for CATV situations. I will say this tho'. No matter what the 'in-house'
measurement system is for that discipline, ultimately you'll end up referring
it to those "good-ol'-time" - frequency / power. Which of course is where I
entered this dB fest -)


Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Did'nt say THEY wern't ( did I?). Don't think I did anyway. But if I had, it
was in the context of relating it to the audio type of discussion that was
going on in here. (And yes, I do know about mixing etc). As far as in-band -
there's no argument from me about that.



I did not say that they were used (in-band). I mentioned them and thinking, at
the same time of RF signal generators / RF amps - all of which should have low
spectral impurity e.g. second / third harmonics. In those situations filters
are effective. (and absolutely requisite in some instances)


Not necessarily. It merely means I did not understand what you were getting
at. Quite often things are clear in our minds when we write but due to to
cultural differences or terminology habits, there can be some momentary
interruption to the cross flow of understanding.



I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)

Bob Stanton

Bazza wrote in message


No, Bob. I disagree. I am considering and restricting myself to pretty much
ONLY RF engineering in its broadest context of transmitters and band systems.
I'd go a bit further and say that although CATV is ubiquitous it's not the
"raison d'etre" for an RF engineers life -(. True, you could make a case for
very wide band situations perhaps such as CATV but this implies an agreed
definition of what constitutes a wide band and, as I admitted before, I cannot
speak for CATV situations. I will say this tho'. No matter what the 'in-house'
measurement system is for that discipline, ultimately you'll end up referring
it to those "good-ol'-time" - frequency / power. Which of course is where I
entered this dB fest -)


Oh no, quite the opposit. The makers of RF broadband amplifiers (CATV
RF amplifiers, for example) are *very* interested in distortion.

Did'nt say THEY wern't ( did I?). Don't think I did anyway. But if I had, it
was in the context of relating it to the audio type of discussion that was
going on in here. (And yes, I do know about mixing etc). As far as in-band -
there's no argument from me about that.



I did not say that they were used (in-band). I mentioned them and thinking, at
the same time of RF signal generators / RF amps - all of which should have low
spectral impurity e.g. second / third harmonics. In those situations filters
are effective. (and absolutely requisite in some instances)


Not necessarily. It merely means I did not understand what you were getting
at. Quite often things are clear in our minds when we write but due to to
cultural differences or terminology habits, there can be some momentary
interruption to the cross flow of understanding.



I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)

Bob Stanton

On 23 Jan 2004 03:16:49 -0800, (Bob-Stanton) wrote:


I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)


That's ... "That's too bad"
^^^
Heh. Gotcha -)

On 23 Jan 2004 03:16:49 -0800, (Bob-Stanton) wrote:


I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)


That's ... "That's too bad"
^^^
Heh. Gotcha -)

On 23 Jan 2004 03:16:49 -0800, (Bob-Stanton) wrote:


I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)


That's ... "That's too bad"
^^^
Heh. Gotcha -)

On 23 Jan 2004 03:16:49 -0800, (Bob-Stanton) wrote:


I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)


That's ... "That's too bad"
^^^
Heh. Gotcha -)

On Sat, 24 Jan 2004 09:16:42 +1100, Bazza wrote:

On 23 Jan 2004 03:16:49 -0800, (Bob-Stanton) wrote:


I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)


That's ... "That's too bad"
^^^
Heh. Gotcha -)

---
You forgot the period.

--
John Fields

On Sat, 24 Jan 2004 09:16:42 +1100, Bazza wrote:

On 23 Jan 2004 03:16:49 -0800, (Bob-Stanton) wrote:


I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)


That's ... "That's too bad"
^^^
Heh. Gotcha -)

---
You forgot the period.

--
John Fields

On Sat, 24 Jan 2004 09:16:42 +1100, Bazza wrote:

On 23 Jan 2004 03:16:49 -0800, (Bob-Stanton) wrote:


I think we petty much agree on most things. We are looking at the same
things, from slightly different perspective.

I don't think there is much we can argue about.

That's to bad. :-)


That's ... "That's too bad"
^^^
Heh. Gotcha -)

---
You forgot the period.

--
John Fields