[apa]

I recently acquired a used Tektronix 2430A with a P6122 probe that is
showing a good deal of noise on lower level traces and I'm wondering
if it is "normal" or if there may be something wrong with the scope or
probe. A 140 mV P-P sine wave from a Minirator is showing about 5 mV
of noise on a sine wave:

P6122http://img39.imageshack.us/img39/9206/img1851m.jpg

I also see the same sort of noise on a square wave from my signal
generator connected to the scope with a coax cable:

http://img192.imageshack.us/img192/9158/img1849fn.jpg

It shows the same thing when connected to the internal calibration
oscillator on the scope.

I really have only a very basic knowledge of oscilloscope use and I
can't remember measuring signal this low with my old BK Precision
2120. I have the Tektronix on a 1 week evaluation and can return it if
I choose, but I wouldn't want to do that if there isn't anything wrong
with it.

I tried it with the TEK P6122 probe that came with the scope and with
the generic scope probe from my old BK 2120 and the noise was worse
with the generic probe.

Is it normal to be fighting noise in this range with scope
measurements?

Would this be a common issue with a maladjusted scope that would be
cleared up with a calibration (this one was calibrated 2 years ago
according to the sticker on it)?

Are there other tests I could run to confirm normal functioning?

Any help would be much appreciated.

Thanks, Andy

[Mike Rivers]

On 3/27/2012 6:27 AM, apa wrote:
I recently acquired a used Tektronix 2430A with a P6122 probe that is
showing a good deal of noise on lower level traces and I'm wondering
if it is "normal" or if there may be something wrong with the scope or
probe. A 140 mV P-P sine wave from a Minirator is showing about 5 mV
of noise on a sine wave:

Do you have another test source other than the Minirator? I
have an MR-Pro and an MR-1 and both are a bit noisy at low
levels, though it's not usually a problem until getting down
to levels around -60 dBu, some 30 dB lower than what you're
looking at. The old style with the swing-out XLR connector
had connector problems that requires a little fiddling with
either hte XLR or RCA connector to get a quiet signal. The
MR-PRO doesn't have an output attenuator, so the level
adjustment is done digitally - lower level = fewer bits =
more noise. They recommend putting a 20 or 40 dB pad after
the output for testing with low levels.

Be that as it may, it looks like "digital" noise and that
might be a characteristic of the scope. I'd check it with a
shorted input and see if a straight line looks ragged (like
the top and bottom of your square wave). If it does, I'd
return the scope. It may or may not be defective, but either
way it's not suitable if you want to be looking at low level
audio signals.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[apa]

On Mar 27, 8:02*am, Mike Rivers wrote:
On 3/27/2012 6:27 AM, apa wrote:

I recently acquired a used Tektronix 2430A with a P6122 probe that is
showing a good deal of noise on lower level traces and I'm wondering
if it is "normal" or if there may be something wrong with the scope or
probe. A 140 mV P-P sine wave from a Minirator is showing about 5 mV
of noise on a sine wave:

Do you have another test source other than the Minirator? I
have an MR-Pro and an MR-1 and both are a bit noisy at low
levels, though it's not usually a problem until getting down
to levels around -60 dBu, some 30 dB lower than what you're
looking at. The old style with the swing-out XLR connector
had connector problems that requires a little fiddling with
either hte XLR or RCA connector to get a quiet signal. The
MR-PRO doesn't have an output attenuator, so the level
adjustment is done digitally - lower level = fewer bits =
more noise. They recommend putting a 20 or 40 dB pad after
the output for testing with low levels.

Be that as it may, it looks like "digital" noise and that
might be a characteristic of the scope. I'd check it with a
shorted input and see if a straight line looks ragged (like
the top and bottom of your square wave). If it does, I'd
return the scope. It may or may not be defective, but either
way it's not suitable if you want to be looking at low level
audio signals.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com- useful and
interesting audio stuff

Thanks Mike. It does look the same with a shorted input. I've never
had a digital scope so I don't know what's normal for digital noise. I
have a lot of higher level signals to work with too and the storage
function is really nice to have so I may keep it if it's not overtly
dysfunctional.

Best, Andy

[Scott Dorsey]

apa wrote:

Thanks Mike. It does look the same with a shorted input. I've never
had a digital scope so I don't know what's normal for digital noise. I
have a lot of higher level signals to work with too and the storage
function is really nice to have so I may keep it if it's not overtly
dysfunctional.

The digital scope has the same front end as the analogue scope... it
does not digitize the signal until it's already been amplified. So the
noise should not be any different.

Most of those scopes have 8 or 12 bit resolution, and no anti-aliasing.
The resolution is high enough for the LCD display, but if the display
were much larger (or if you used a trace-expand function) it might not be.
Still, if that were the case, you wouldn't see noise so much as jaggies.

The lack of anti-aliasing is what really gets me using the digital scopes.
When you have high frequency junk, instead of seeing smearing, you see
weird waveform changes. You can tell this is going on because when you
change the sweep rate on the scope, the waveform changes, so it's not a
major problem. But you have to bother to look for it, unlike the smearing
on analogue scopes that you can't help but see.

I find the latency on the digital scopes makes tweak-and-peak stuff like
setting tape machine azimuth to be very frustrating. On the other hand,
the ability to do very very low speed sweeps is wonderful for doing swept
sine testing, and and you can see glitches and popcorn noise much more
easily with the ability to freeze a waveform and go back to it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[apa]

When I short the probe I get the same sort of "noise" on an otherwise
straight line at 0 volts.

On Mar 27, 9:49*am, "Soundhaspriority" wrote:
What happens when you short the probe tip?

Bob Morein
(310) 237-6511

"apa" wrote in message

...







I recently acquired a used Tektronix 2430A with a P6122 probe that is
showing a good deal of noise on lower level traces and I'm wondering
if it is "normal" or if there may be something wrong with the scope or
probe. A 140 mV P-P sine wave from a Minirator is showing about 5 mV
of noise on a sine wave:

P6122http://img39.imageshack.us/img39/9206/img1851m.jpg

I also see the same sort of noise on a square wave from my signal
generator connected to the scope with a coax cable:

http://img192.imageshack.us/img192/9158/img1849fn.jpg

It shows the same thing when connected to the internal calibration
oscillator on the scope.

I really have only a very basic knowledge of oscilloscope use and I
can't remember measuring signal this low with my old BK Precision
2120. I have the Tektronix on a 1 week evaluation and can return it if
I choose, but I wouldn't want to do that if there isn't anything wrong
with it.

I tried it with the TEK P6122 probe that came with the scope and with
the generic scope probe from my old BK 2120 and the noise was worse
with the generic probe.

Is it normal to be fighting noise in this range with scope
measurements?

Would this be a common issue with a maladjusted scope that would be
cleared up with a calibration (this one was calibrated 2 years ago
according to the sticker on it)?

Are there other tests I could run to confirm normal functioning?

Any help would be much appreciated.

Thanks, Andy

[MarkK]

Is this a 10x probe?

If you are reading 5mV of noise on a 10x probe, that is 0.5mV of noise of
actual noise in the scope.

Even if it a x1 probe, that does not seem like an excess amount of noise.
The trace on my 60MHz scope looks a little fuzzy on the highest gain setting
which is 5mV on x1 or 50mV on 10x.

Its probably perfectly normal.

Mark


"apa" wrote in message
...
When I short the probe I get the same sort of "noise" on an otherwise
straight line at 0 volts.

On Mar 27, 9:49 am, "Soundhaspriority" wrote:
What happens when you short the probe tip?

Bob Morein
(310) 237-6511

"apa" wrote in message

...







I recently acquired a used Tektronix 2430A with a P6122 probe that is
showing a good deal of noise on lower level traces and I'm wondering
if it is "normal" or if there may be something wrong with the scope or
probe. A 140 mV P-P sine wave from a Minirator is showing about 5 mV
of noise on a sine wave:

P6122http://img39.imageshack.us/img39/9206/img1851m.jpg

I also see the same sort of noise on a square wave from my signal
generator connected to the scope with a coax cable:

http://img192.imageshack.us/img192/9158/img1849fn.jpg

It shows the same thing when connected to the internal calibration
oscillator on the scope.

I really have only a very basic knowledge of oscilloscope use and I
can't remember measuring signal this low with my old BK Precision
2120. I have the Tektronix on a 1 week evaluation and can return it if
I choose, but I wouldn't want to do that if there isn't anything wrong
with it.

I tried it with the TEK P6122 probe that came with the scope and with
the generic scope probe from my old BK 2120 and the noise was worse
with the generic probe.

Is it normal to be fighting noise in this range with scope
measurements?

Would this be a common issue with a maladjusted scope that would be
cleared up with a calibration (this one was calibrated 2 years ago
according to the sticker on it)?

Are there other tests I could run to confirm normal functioning?

Any help would be much appreciated.

Thanks, Andy

[Gareth Magennis]

"apa" wrote in message
...
I recently acquired a used Tektronix 2430A with a P6122 probe that is
showing a good deal of noise on lower level traces and I'm wondering
if it is "normal" or if there may be something wrong with the scope or
probe. A 140 mV P-P sine wave from a Minirator is showing about 5 mV
of noise on a sine wave:

P6122http://img39.imageshack.us/img39/9206/img1851m.jpg

I also see the same sort of noise on a square wave from my signal
generator connected to the scope with a coax cable:

http://img192.imageshack.us/img192/9158/img1849fn.jpg

It shows the same thing when connected to the internal calibration
oscillator on the scope.

I really have only a very basic knowledge of oscilloscope use and I
can't remember measuring signal this low with my old BK Precision
2120. I have the Tektronix on a 1 week evaluation and can return it if
I choose, but I wouldn't want to do that if there isn't anything wrong
with it.

I tried it with the TEK P6122 probe that came with the scope and with
the generic scope probe from my old BK 2120 and the noise was worse
with the generic probe.

Is it normal to be fighting noise in this range with scope
measurements?

Would this be a common issue with a maladjusted scope that would be
cleared up with a calibration (this one was calibrated 2 years ago
according to the sticker on it)?

Are there other tests I could run to confirm normal functioning?

Any help would be much appreciated.

Thanks, Andy



This site has a screnshot very similar to yours:

http://www.ecrunch.com/listing/Tektr...illoscope.html



Gareth.