[Phil Allison]

"don pearce ASININE PITA smug ****** "


"Richard Crowley Vile Arse Licker "

If you are trying to use a balanced
mic, then the cable is unsuitable because it is unbalanced.

** Not true at all !!

There is NO reason not to use a (suitable) co-axial type cable with a
microphone - either low or high impedance.

Despite all the nonsense you WILL have read elsewhere, co-axial
cables have as good or better rejection of external hum and noise
sources as do balanced twin wire cables.

Try it out if you don't believe this.

Of course a proper microphone cable is SCREENED balanced twisted pair,


** Exactly what I was referring to above.

Mic cable IS a balanced twin wire cable.


Having trouble spotting the capital letters, are you?


** Go no idea what the term " mic cable " refers to - eh ??

****WIT ??

Do go have a look at some one day.



(yes, I saw yours, and that is what prompted this question, the relevance
obviously passed you by).


** Go get utterly ****ed -

you VILE, SMUG ILLITERATE pile of autistic **** !!



A poorly screened coax cable such as TV coax has only a part of the
first of those


** It ain't necessarily poorly screened and it ain't necessarily what I
just posted about.

Do learn to read sometime - ****wit.


we know exactly what this cable is - and yes it is poorly screened.


** It ain't necessarily poorly screened and it ain't necessarily what I
just
posted about.

Do learn to read sometime -

you stinking, arrogant pile of demented ****.



has only a part of the first of those ..


** Not true of co-axial cable in general.

Do learn to read sometime - ****wit.


so this claim is clearly nonsensical.

** Not at all -

your irrelevant & asinine claims are nonsensical

- ****wit.


If it were true, professional microphone and mixer companies would not
be going to the trouble of designing balanced kit.


** More completely irrelevant nonsense.


Irrelevant is it?


** Your illogical point is what is irrelevant.

Do learn to read sometime -

you stinking, arrogant pile of demented ****.


Tell that to Neve, Neumann, Shure, Sennheiser, Leevers Rich - need I go
on?


** Feel free to top yourself anytime - Don.

It would do the whole planet a small favour.

One less ASD ****ed arsehole stinking it up.




" Despite all the nonsense you WILL have read elsewhere, co-axial
cables
have as good or better rejection of external hum and noise sources as do
balanced twin wire cables. Try it out if you don't believe this. "

Obviously YOU need to do this too - ****wit.

Since you are so PIG ignorant of the basic physics of co-axial cable.


I appear to have a vastly better grasp of the topic than you,


** You appear to have a monstrous, malignant tumour growing in you fat,
stupid head.

At least, I sincerely hope that is indeed the case.



not surprising really when you consider that I have designed ultra low
noise microwave measuring equipment.


** Whaaaaaaaatttttt ???????????

ROTFLMAO !!!

What totally IRRELEVANT ******** !!!

Typical smug puke from the " Don Pearce " cretin

wot a ****ING ARROGANT NUT CASE !!!




..... Phil

[Phil Allison]

"Chris Siz"

I am the OP and as you can probably tell I am no electronics or
radio expert. However even my limited knowledge struggles to
believe some of the points you have made.


** Always seems hard to believe the facts when you know very little about
some matter.

Cos the truth is never as simple as you would like to be.


Forgive me if it's more obvious to others but your's is not some
sort of funny posting is it?


** Certainly yours is very funny.

Looks every inch like some **** head's pathetic troll.




...... Phil

[Don Pearce]

On Sun, 04 May 2008 12:51:35 +0100, Chris S
wrote:

On Sun 04 May 2008 02:23:08, Michael A. Terrell wrote:


Walt Davidson wrote:

On Sat, 03 May 2008 11:05:41 -0700, Kevin McMurtrie
wrote:

TV coax is very brittle. The inner wire is copper-plated steel
and the outer shield is aluminum wire and aluminum foil. It
will quickly crack where it meets the connectors.

What planet do you live on? I have never seen TV coax as you
describe. Coax with copper-plated steel inner conductor is
mostly used as data cable (ethernet).


Then you've never seen the wire used by cable TV and Satellite TV
companies. Pure copper is too expensive these days, and too soft
for repeated flexing. If you want to pay over a dollar a foot for
copper core TV coax, go ahead. The last time I had to buy some it
was about eight times the price of the foil shield W/braid TV
coax, and useless for UHF. Use a magnet, and see for yourself.
The copper plating smears when cut with dykes, and makes the
coated steel appear to be solid copper.


If copper is soft then wouldn't that make it good for repeated
flexing in the sense that copper isn't so stiff that it wouldn't
split or crack?

If it is a cable that needs to be moved around and flexed, then it
absolutely has to be stranded. Solid core will always fatigue and
break in those circumstances.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Michael A. Terrell]

Chris S wrote:

On Sun 04 May 2008 04:28:55, Jeff Liebermann wrote:

Incidentally, I blundered across this data sheet for RG-6/u. They
can make it just about any way you want it, and still call it
RG-6/u. Note the line with:
6) Braiding coverage: Between 30 - 97% available;
I can't imagine who would want to buy 30% coverage outer
shielding.
http://www.tootoo.com/supplier/produ...9/RG6%252fU.ht
ml


I too have started to feeling that there is a heck of lot more
variation than I realised in how coax cables can be made and yet are
still conform to some particular technical specification.

I came across some interesting articles at "abc cables". Here are some
which caught my eye. http://www.abccables.com/technical-support.html

Wire? or Cable?
RG6 Copper vs. Copper Clad Steel
RG59 vs. RG6
Better Copper?

I would like to get other (supplier's) info as that site is quite
useful. Has anyone got any links to these sort of explanatory
articles?


You can slap RG- numbers on anything. It stopped being a military
standard a long time ago. Belden, Alpha, Times wire websites should
have some good white papers. RG meant 'Radio Guide', and all early coax
was braided copper shielding. Their is still some RF coax made this way,
but it uses teflon and silver plated copper and is VERY expensive.

http://www.belden.com/pdfs/Cable101/Shielding.pdf page 32 states 'Braid
is for low frequency, foil for high frequency'.

http://www.belden.com/pdfs/03Belden_Master_Catalog/06Coaxial_Cables/06Coaxial_Cables.pdf
is the coaxial cable part of the Belden catalog. about 4 MB download.

http://www.belden.com/pdfs/03Belden_Master_Catalog/2006_Belden_Catalog.pdf
is their full catalog, about 38 MB download.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

[Michael A. Terrell]

Chris S wrote:

If copper is soft then wouldn't that make it good for repeated
flexing in the sense that copper isn't so stiff that it wouldn't
split or crack?


Copper 'work hardens' when flexed. Over time it develops cracks, then
breaks. Stranded wire uses smaller conductors and has less problems per
conductor, due to a larger bending radius VS the diameter of the
conductor. The steel center conductor is meant for permanent
installation, but it holds up better on the bench that solid copper
coax.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

[Michael A. Terrell]

Dead Paul wrote:

no pickup inside coax.


Really? Then you don't know much about Coaxial cables, shielding
effectiveness, signal ingression and a dozen other topics. In other
words, no single shield is 100% effective.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

[Don Pearce]

On Sun, 04 May 2008 11:15:45 -0400, "Michael A. Terrell"
wrote:

Dead Paul wrote:

no pickup inside coax.


Really? Then you don't know much about Coaxial cables, shielding
effectiveness, signal ingression and a dozen other topics. In other
words, no single shield is 100% effective.

And of course unless it is made of soft iron or mumetal, it doesn't
shield magnetically at all.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Richard Crowley]

"don pearce" wrote...
Phil Allison wrote:
"Richard Crowley"
(1) Is it ok to use this sort of coax for a microphone?
Not enough details to answer your question adequately.
First of all, the kinds of microphones used for audio
applications (reinforcement, recording, etc.) are usually
balanced and require cable with two inner wires and an
outside shield/screen. If you are trying to use a balanced
mic, then the cable is unsuitable because it is unbalanced.

** Not true at all !!

Of course a proper microphone cable is SCREENED balanced twisted pair, so
it enjoys the multiple benefits of electric screening by the outer, the
common mode nature of any residual interference and magnetic interference
cancellation by the twist in the balanced pair. A poorly screened coax
cable such as TV coax has only a part of the first of those so this claim
is clearly nonsensical. If it were true, professional microphone and mixer
companies would not be going to the trouble of designing balanced kit.

Don, please don't feed the troll.

The signal-to-noise ratio from Mr. Allison is so poor that he is
better to be filtered completely out.

[Richard Crowley]

"Dead Paul" wrote in ...
Good quality coax will do the job if you don't mind the impedance mismatch
and if you want balanced line then you could use a pair of coax feeds in
parallel (impedance about 100 ohms for rg58). Also there's coax and
there's coax, I've seen rg58 like TV down-lead and others like shrunk down
UR67M.

There is no "impedance mismatch" at audio frequencies in this
application.

[Don Pearce]

On Sun, 4 May 2008 08:20:22 -0700, "Richard Crowley"
wrote:

"don pearce" wrote...
Phil Allison wrote:
"Richard Crowley"
(1) Is it ok to use this sort of coax for a microphone?
Not enough details to answer your question adequately.
First of all, the kinds of microphones used for audio
applications (reinforcement, recording, etc.) are usually
balanced and require cable with two inner wires and an
outside shield/screen. If you are trying to use a balanced
mic, then the cable is unsuitable because it is unbalanced.

** Not true at all !!

Of course a proper microphone cable is SCREENED balanced twisted pair, so
it enjoys the multiple benefits of electric screening by the outer, the
common mode nature of any residual interference and magnetic interference
cancellation by the twist in the balanced pair. A poorly screened coax
cable such as TV coax has only a part of the first of those so this claim
is clearly nonsensical. If it were true, professional microphone and mixer
companies would not be going to the trouble of designing balanced kit.

Don, please don't feed the troll.

The signal-to-noise ratio from Mr. Allison is so poor that he is
better to be filtered completely out.


Sorry, he normally resides in my killfile where he belongs, but every
now and then I have to reconfigure something and he gets out.

He's back in there with a shot of Ketamine now.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Richard Crowley]

"Don Pearce" wrote...
As I said in my first reply, if I was forced to use coax for a
microphone, domestic TV grade would be a very poor choice because in
general it has perhaps no more than 10% screening (just enough in fact
to give the cable a stable characteristic impedance, but no more).

That may be the case over there (although I doubt it).
Over on our side of the earth, RF cables, and especially
those intended for television use are 100% shielded.
Because if they are not, it starts causing problems.
Problems for the cable operators when RF leaks (in
either direction) between the TV station on channel X
and the over-the-air signal of the same station on the
same frequency. This is a chronic problem in some of
the poorer-maintained systems.

And problems for individuals even with just a run of
several meters to a rooftoop antenna because of the
increased susceptability to RFI, particularly in remote
regions where the signal is weak to start with.

RF coax made for cable TV use have foil shields plus
a few strands of wire braid around the foil. In fact many
of them even have a double foil shield.

Don't mistake the wire braid (which may, indeed be only
10% coverage) for the actual outer shield of the coax
which is the active portion.

Microphone signals are too small to mess around this way.
Decent audio grade cable has screening approaching 100%.

And out in remote rural areas, RF signals are of the same
order.

[Don Pearce]

On Sun, 4 May 2008 08:32:49 -0700, "Richard Crowley"
wrote:

RF coax made for cable TV use have foil shields plus
a few strands of wire braid around the foil. In fact many
of them even have a double foil shield.

Don't mistake the wire braid (which may, indeed be only
10% coverage) for the actual outer shield of the coax
which is the active portion.

Yup, but the stuff we are discussing here has just a very loose braid.
Have a look at the second pic on this page - low loss TV coax.

http://www.megalithia.com/elect/cable/index.html

d
--
Pearce Consulting
http://www.pearce.uk.com

[Michael A. Terrell]

Jeff Liebermann wrote:

On Sat, 03 May 2008 21:23:08 -0400, "Michael A. Terrell"
wrote:

Use a magnet, and see for yourself. The copper plating smears
when cut with dykes, and makes the coated steel appear to be solid
copper.

Trivia:
Dike = Diagonal Cutters
http://en.wikipedia.org/wiki/Diagonal_pliers
Dyke = Lesbian
http://en.wikipedia.org/wiki/Dyke_(lesbian)
Dyke or Dike = Earthen wall or dam
http://en.wikipedia.org/wiki/Dike_%28construction%29

Methinks "dikes" would be the correct spelling.


I have seen it written as dykes more often, but who knows? Are you
saying lesbians can't cut wire? ;-)?


--
http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm

[Richard Crowley]

"Don Pearce" wrote ...
"Richard Crowley"
wrote:

RF coax made for cable TV use have foil shields plus
a few strands of wire braid around the foil. In fact many
of them even have a double foil shield.

Don't mistake the wire braid (which may, indeed be only
10% coverage) for the actual outer shield of the coax
which is the active portion.

Yup, but the stuff we are discussing here has just a very loose braid.
Have a look at the second pic on this page - low loss TV coax.

http://www.megalithia.com/elect/cable/index.html

What is that stuff good for?!
I've never seen anything like that over here. It can't be
useful for low-level signals (receiving, audio, etc.) any
place where there is any RFI.

OTOH, they make an intentionally "lossy" coaxial cable
(one brand name is "Radiax") which is used for distributed
Tx/Rx (such as running a cable through a tunnel to provide
cell service underground, etc.) That stuff has holes all along
the length to deliberately leak RF along the way.

[Dead Paul]

On Sun, 04 May 2008 08:32:49 -0700, Richard Crowley wrote:

"Don Pearce" wrote...
As I said in my first reply, if I was forced to use coax for a
microphone, domestic TV grade would be a very poor choice because in
general it has perhaps no more than 10% screening (just enough in fact
to give the cable a stable characteristic impedance, but no more).

That may be the case over there

Over there? Over here we find lots of 72 ohm tv coax on sale in the diy
stores which has very poor screening. In fact I'd say the majority of
terrestrial tv antennas in the Uk are wired with it.

(although I doubt it). Over on our side of
the earth, RF cables, and especially those intended for television use are
100% shielded. Because if they are not, it starts causing problems.
Problems for the cable operators

Well yes, cable tv operators even over here use much higher quality coax.

snip

Don't mistake the wire braid (which may, indeed be only 10% coverage) for
the actual outer shield of the coax which is the active portion.

I don't think any regular in this ng is going to make a mistake like that.

Microphone signals are too small to mess around this way. Decent audio
grade cable has screening approaching 100%.

And out in remote rural areas, RF signals are of the same order.

Most areas here (UK) have excellent analogue signal strength.

--
___ _______ ___ ___ ___ __ ____
/ _ \/ __/ _ | / _ \ / _ \/ _ |/ / / / /
/ // / _// __ |/ // / / ___/ __ / /_/ / /__
/____/___/_/ |_/____/ /_/ /_/ |_\____/____/

[Don Pearce]

On Sun, 4 May 2008 10:09:34 -0700, "Richard Crowley"
wrote:

"Don Pearce" wrote ...
"Richard Crowley"
wrote:

RF coax made for cable TV use have foil shields plus
a few strands of wire braid around the foil. In fact many
of them even have a double foil shield.

Don't mistake the wire braid (which may, indeed be only
10% coverage) for the actual outer shield of the coax
which is the active portion.

Yup, but the stuff we are discussing here has just a very loose braid.
Have a look at the second pic on this page - low loss TV coax.

http://www.megalithia.com/elect/cable/index.html

What is that stuff good for?!
I've never seen anything like that over here. It can't be
useful for low-level signals (receiving, audio, etc.) any
place where there is any RFI.

It is good for absolutely nothing, and nowadays resides only in cut
price electrical stores and old boxes in attics.

OTOH, they make an intentionally "lossy" coaxial cable
(one brand name is "Radiax") which is used for distributed
Tx/Rx (such as running a cable through a tunnel to provide
cell service underground, etc.) That stuff has holes all along
the length to deliberately leak RF along the way.

I know Andrew's Radiax very well - I've specified it for distributing
VHF in tunnels.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Dead Paul]

On Sun, 04 May 2008 15:17:37 +0000, Don Pearce wrote:

On Sun, 04 May 2008 11:15:45 -0400, "Michael A. Terrell"
wrote:

Dead Paul wrote:

no pickup inside coax.


Really? Then you don't know much about Coaxial cables, shielding
effectiveness, signal ingression and a dozen other topics. In other
words, no single shield is 100% effective.

And of course unless it is made of soft iron or mumetal, it doesn't shield
magnetically at all.

coax doesn't shield in that way. It works by cancellation and eddy current
effects duh!



d

--
___ _______ ___ ___ ___ __ ____
/ _ \/ __/ _ | / _ \ / _ \/ _ |/ / / / /
/ // / _// __ |/ // / / ___/ __ / /_/ / /__
/____/___/_/ |_/____/ /_/ /_/ |_\____/____/

[Don Pearce]

On Sun, 04 May 2008 18:24:15 +0100, Dead Paul
wrote:

On Sun, 04 May 2008 15:17:37 +0000, Don Pearce wrote:

On Sun, 04 May 2008 11:15:45 -0400, "Michael A. Terrell"
wrote:

Dead Paul wrote:

no pickup inside coax.


Really? Then you don't know much about Coaxial cables, shielding
effectiveness, signal ingression and a dozen other topics. In other
words, no single shield is 100% effective.

And of course unless it is made of soft iron or mumetal, it doesn't shield
magnetically at all.

coax doesn't shield in that way. It works by cancellation and eddy current
effects duh!

Coax used normally deals with magnetic fields by having effectively no
magnetic loop area - the two conductors are running along an identical
centre line so there is no magnetic loop to pick up a signal. As soon
as you run a signal along two pieces of coax in differential mode, the
area encompassed by the resulting loop is susceptible to magnetic
pickup. Depending on how you deal with the screens, you may have a
shorted turn to help out, but maybe not. Think of how a direction
finding loop antenna works - it is fully shielded (apart from a small
break to prevent the shorted turn) and works on the magnetic component
of the received signal alone.

Twisted pair inside a single screen deals with all these potential
problems.

d
--
Pearce Consulting
http://www.pearce.uk.com

[Dead Paul]

On Sun, 04 May 2008 17:39:09 +0000, Don Pearce wrote:

On Sun, 04 May 2008 18:24:15 +0100, Dead Paul wrote:

On Sun, 04 May 2008 15:17:37 +0000, Don Pearce wrote:

On Sun, 04 May 2008 11:15:45 -0400, "Michael A. Terrell"
wrote:

Dead Paul wrote:

no pickup inside coax.


Really? Then you don't know much about Coaxial cables, shielding
effectiveness, signal ingression and a dozen other topics. In other
words, no single shield is 100% effective.

And of course unless it is made of soft iron or mumetal, it doesn't
shield magnetically at all.

coax doesn't shield in that way. It works by cancellation and eddy
current effects duh!

Coax used normally deals with magnetic fields by having effectively no
magnetic loop area - the two conductors are running along an identical
centre line so there is no magnetic loop to pick up a signal.

Radial field in the coax resulting in cancellation.


As soon as
you run a signal along two pieces of coax in differential mode, the area
encompassed by the resulting loop is susceptible to magnetic pickup.
Depending on how you deal with the screens, you may have a shorted turn to
help out, but maybe not. Think of how a direction finding loop antenna
works - it is fully shielded (apart from a small break to prevent the
shorted turn) and works on the magnetic component of the received signal
alone.

that's all true, i have built several loops of that type for HF.

Twisted pair inside a single screen deals with all these potential
problems.

In agree it's better than two lengths of coax as balanced line but didn't
the discussion centre around using coax as audio lead? I'm sure anyone in
their right mind would use audio cable if they had it available.


d

--
___ _______ ___ ___ ___ __ ____
/ _ \/ __/ _ | / _ \ / _ \/ _ |/ / / / /
/ // / _// __ |/ // / / ___/ __ / /_/ / /__
/____/___/_/ |_/____/ /_/ /_/ |_\____/____/

[Don Pearce]

On Sun, 04 May 2008 18:47:17 +0100, Dead Paul
wrote:

On Sun, 04 May 2008 17:39:09 +0000, Don Pearce wrote:

On Sun, 04 May 2008 18:24:15 +0100, Dead Paul wrote:

On Sun, 04 May 2008 15:17:37 +0000, Don Pearce wrote:

On Sun, 04 May 2008 11:15:45 -0400, "Michael A. Terrell"
wrote:

Dead Paul wrote:

no pickup inside coax.


Really? Then you don't know much about Coaxial cables, shielding
effectiveness, signal ingression and a dozen other topics. In other
words, no single shield is 100% effective.

And of course unless it is made of soft iron or mumetal, it doesn't
shield magnetically at all.

coax doesn't shield in that way. It works by cancellation and eddy
current effects duh!

Coax used normally deals with magnetic fields by having effectively no
magnetic loop area - the two conductors are running along an identical
centre line so there is no magnetic loop to pick up a signal.

Radial field in the coax resulting in cancellation.


As soon as
you run a signal along two pieces of coax in differential mode, the area
encompassed by the resulting loop is susceptible to magnetic pickup.
Depending on how you deal with the screens, you may have a shorted turn to
help out, but maybe not. Think of how a direction finding loop antenna
works - it is fully shielded (apart from a small break to prevent the
shorted turn) and works on the magnetic component of the received signal
alone.

that's all true, i have built several loops of that type for HF.

Twisted pair inside a single screen deals with all these potential
problems.

In agree it's better than two lengths of coax as balanced line but didn't
the discussion centre around using coax as audio lead? I'm sure anyone in
their right mind would use audio cable if they had it available.


Yup, that's right where this all started. Should he use poorly
screened coax as a microphone cable (I wouldn't be worried about it at
line level). I think the general answer is that while he might just
get away with it, it isn't a good idea and some properly screened
audio cable would be better.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Jeff Liebermann]

On Sun, 04 May 2008 11:11:40 -0400, "Michael A. Terrell"
wrote:

Chris S wrote:
If copper is soft then wouldn't that make it good for repeated
flexing in the sense that copper isn't so stiff that it wouldn't
split or crack?

Copper 'work hardens' when flexed. Over time it develops cracks, then
breaks. Stranded wire uses smaller conductors and has less problems per
conductor, due to a larger bending radius VS the diameter of the
conductor. The steel center conductor is meant for permanent
installation, but it holds up better on the bench that solid copper
coax.

Yep. Way back in the 1960's, I was installing 2way radios in various
vehicles. Someone found some RG-58/u, with a solid center conductor.
I was told to use it. About 100 vehicles later, someone declared that
solid coax was a bad idea. Management decided that it would replace
all the coax, but only after evidence of the first failure. So, we
waited, and waited, and waited. I was long gone when one of the coax
cables finally failed, about 5 years or 150,000 miles later.

Fast forward to the early 1990's and cellular telephone installs. At
the time, the average cell phone was big, boxy, heavy, and ugly. The
connector of fashion was the TNC. Once again, some dealers were
installing solid center conductor coax in the vehicles. They would
last about a month and then break. Huh? Solid center conductor
RG-58/u works in 100 buses for 5 years, but not in a passenger car for
a month? Something is obviously different.

It's the connector. In the 1960's we soldered everything. The common
PL-259 and UG-175 adapter was as sloppy a connection that could have
been mis-designed. 30 years later, everyone was crimping the
connectors. The breakage was always at the connector. The crimper
was dinging the center conductor. The sharp edge on the rear of the
center pin did the rest. Soldering the center pin and the longer
distance between the crimp and the point at which the cable will begin
to flex (UHF versus TNC) did much to prevent breakage.

All RG-6/u "type" cables are not all solid center conductor. Belden
Brilliance 1694F is flexible.
http://www.belden.com/pdfs/Prodbull/NP233.pdf
at about $0.70/ft. However, it cannot be used with Type-F connectors.
The data sheet mumbles:
"1694F is intended for use with connectors designed for 1694A"
which is not very helpful.

The foil outer shield usually tears in a flex test long before work
hardening does anything to the center conductor.

I've watched cable flex testers locally:
http://www.ideinc.com/plan_cycle.html
http://www.ideinc.com/plan_tester.html
(Bring hearing protection). These simulate normal cable bending on
telephone headsets. The flexing is far more radical than anything
that would be encountered with RF coax cable. I asked if they had
ever tried flexing RF type coax cable. As I vaguely recall, neither
solid or stranded center conductor coax cables survived for very long,
but I don't recall the numbers. I'll ask.

Incidentally, there's also the tiny triboelectric noise created by the
mylar coated insulated shield, rubbing against the dielectric:
http://en.wikipedia.org/wiki/Triboelectric_effect
Good microphone cable should be "bonded" (i.e. glued) to prevent this
admittedly tiny noise problem. You're not going to find that in
commodity RF coax cable.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Dave Platt]

In article ,
Michael A. Terrell wrote:

You can slap RG- numbers on anything. It stopped being a military
standard a long time ago. Belden, Alpha, Times wire websites should
have some good white papers. RG meant 'Radio Guide', and all early coax
was braided copper shielding. Their is still some RF coax made this way,
but it uses teflon and silver plated copper and is VERY expensive.

http://www.belden.com/pdfs/Cable101/Shielding.pdf page 32 states 'Braid
is for low frequency, foil for high frequency'.

The RF-type foil-with-some-braid coax (LMR400 is one type) is quite
popular, and does seem to provide good shielding. However, there are
high-frequency (UHF/VHF) applications in which it has a rather evil
reputation. In particular, most repeater operators I know avoid it
like the plague when it comes time to run their primary feedlines.

Practical experience seems to suggest that this sort of construction
is prone to broadband-noise problems when used for duplex
applications... e.g. in a repeater where you're transmitting 25 - 100
watts up the cable in one direction, and also trying to receive a
microvolt-level signal on a nearby frequency at the same time in the
other direction.

The culprit seems to be the fact that the foil and braid don't make
perfect contact throughout the cable - they're not (and cannot be)
soldered together, and the contact between them is simply a
mechanical-pressure contact which is imperfect. There seems to be an
irregular make-and-break effect - I've heard it called "micro-arcing" -
which causes some small amount of the transmitted energy being
rectified and spread around the spectrum as broadband noise. Some of
this noise ends up on the repeater's receiver frequency, and cannot be
filtered out at the receiver... and this competes with the incoming
signal and can swamp it out (a form of receiver desensitization).

It doesn't take much of this noise to be a problem... I figured out
last year that in our repeater application (35 watt transmitter on
145.27 MHz) the transmitter is putting out literally a quadrillion
times more power than the receiver is picking up from a hand-held
radio out at the edge of our service area. Even a tiny fraction of
the transmitter power, rectified into noise, can wipe out the desired
signal.

The remedy for this, in practice, is to use a different type of
cable... one without the foil-and-braid shield construction. One
choice is a good "double braid" shield (which as Michael indicates,
tends to use a silver-plated braid). An even better choice is heliax,
which uses a seamless corrugated-copper shield.

Both are expensive - Andrew 1/2" heliax is edging up towards $3/foot
these days... and both are too stiff to use as microphone cable :-)

The foil-and-braid cables seem to be fine in simplex RF applications,
where you aren't trying to receive and transmit through the same cable
at the same time - the amount of broadband noise being generated is
inconsequential in simplex use.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[Ian Jackson]

In message , Michael A.
Terrell writes

Jeff Liebermann wrote:

On Sat, 03 May 2008 21:23:08 -0400, "Michael A. Terrell"
wrote:

Use a magnet, and see for yourself. The copper plating smears
when cut with dykes, and makes the coated steel appear to be solid
copper.

Trivia:
Dike = Diagonal Cutters
http://en.wikipedia.org/wiki/Diagonal_pliers
Dyke = Lesbian
http://en.wikipedia.org/wiki/Dyke_(lesbian)
Dyke or Dike = Earthen wall or dam
http://en.wikipedia.org/wiki/Dike_%28construction%29

Methinks "dikes" would be the correct spelling.


I have seen it written as dykes more often, but who knows? Are you
saying lesbians can't cut wire? ;-)?

I, for one, have seen at least two who could!
--
Ian

[Kevin McMurtrie]

In article ,
Chris Siz wrote:

On Sat 03 May 2008 22:24:49, Dead Paul wrote:

On Sat, 03 May 2008 19:39:45 +0100, Walt Davidson wrote:

On Sat, 03 May 2008 11:05:41 -0700, Kevin McMurtrie
wrote:

TV coax is very brittle. The inner wire is copper-plated steel
and the outer shield is aluminum wire and aluminum foil. It will
quickly crack where it meets the connectors.

What planet do you live on? I have never seen TV coax as you
describe. Coax with copper-plated steel inner conductor is mostly
used as data cable (ethernet).

You want to see the crap which passes for rg58 at maplin
electronics.



Maplins selling crap merchandise doesn't surprise me. (Though to be
fair, it does sell the odd good item too.)

But where would I go to get half-decent cables in relatively short
lengths (not 50m drums) without paying a fortune for ultra quality
dedicated-hobbyist stuff or exhorbitant delivery charges?

(Trimming response to rec.audio.tech)

I know what you mean. The local stores in Silicon Valley categorize
cable according to glamor rather than performance. I can't go into a
Guitar Center without becoming very angry.

I've purchased good bulk music wire and connectors from he
http://www.best-tronics.com/guitar-cable/index.aspx
Click on "Bulk Cable & Conn" for plain cable by the foot.

It might be US only, though.

--
Block Google's spam and enjoy Usenet again.
Reply with Google and I won't hear from you.

[Kevin McMurtrie]

In article ,
Chris Siz wrote:

On Sat 03 May 2008 19:05:41, Kevin McMurtrie wrote:

In article ,
Chris Siz wrote:

I am in the UK and have a 10m length of some cheap TV aerial
coax. It came from a discount store as a TV coax extension
cable. I measure the cable diameter as 4.8mm.

(1) Is it ok to use this sort of coax for a microphone? I don't
want an impaired audio signal. The length I need to use is 3 to
4 metres.

(2) Is it ok for UHF TV or is it actually quite low grade coax
and prone to interference or mess up the aerial signal?

There are a few differences. TV coax will work in some conditions
but not generally.

TV coax is very brittle. The inner wire is copper-plated steel
and the outer shield is aluminum wire and aluminum foil. It will
quickly crack where it meets the connectors.

TV coax may not pass small audio signals well because of its
aluminum shield. Aluminum is extremely reactive so it is always
coated with a thin oxide layer. Higher voltages can spark through
it and TV RF can capacitively couple through it. Microphone
signals might become distorted. Cable for lower frequencies uses
copper shielding.

Good microphone and instrument cable has an insulation that drains
away static electrical charges. RF coax can contain electrical
charges in the insulation that causes it to act like condenser
microphone.


I am the OP and as you can probably tell I am no electronics or
radio expert. However even my limited knowledge struggles to
believe some of the points you have made.

Forgive me if it's more obvious to others but your's is not some
sort of funny posting is it?

It's not a funny posting. TV signals are high frequency RF and they
behave very differently from audio. The requirements for good TV
performance are very different from microphone cable.

TV needs:
- Very constant RF impedance to reduce signal reflections and smearing.
- Low absorption of very high frequencies in the insulation.
- High conductance along the surface of the center wire.
- Low inductance and capacitance.
- Stretch resistant enough to hang from antennas and rooftops.

Music cable:
- No oxide layers.
- Low capacitance.
- Insulation that does not produce electric noise on impact.
- Resistant to being stepped on and bent.
- Very high shielding coverage to avoid noise pickup from nearby power
cables.

You can buy general purpose coax that works perfectly for both audio and
RF. It's a bit pricey. Since you mentioned it being cheap TV coax, I
doubt it's a good performer outside of TV frequencies.

The real answer is to TRY IT.

--
Block Google's spam and enjoy Usenet again.
Reply with Google and I won't hear from you.

[Jim Gregory]

"Chris Siz" wrote in message
...
I am in the UK and have a 10m length of some cheap TV aerial coax. It
came from a discount store as a TV coax extension cable. I measure the
cable diameter as 4.8mm.

(1) Is it ok to use this sort of coax for a microphone? I don't want
an impaired audio signal. The length I need to use is 3 to 4 metres.

(2) Is it ok for UHF TV or is it actually quite low grade coax and
prone to interference or mess up the aerial signal?


--



[x-posted to 3 relevant groups]

It's fine for connecting a cheapo mic so long as it's kept stationary - as
the coax is nearly rigid and non-pliant compared to good mic cable. If your
mic o/p is balanced, use a 3-conductor [screen + twisted pair] cable and bin
the coax!
Any 2-wire cable (co-ax or not) will do for an aerial feed, if it's kept
short!
Jim

[Jeff Liebermann]

On Sun, 04 May 2008 13:07:17 -0400, "Michael A. Terrell"
wrote:

Jeff Liebermann wrote:

On Sat, 03 May 2008 21:23:08 -0400, "Michael A. Terrell"
wrote:

Use a magnet, and see for yourself. The copper plating smears
when cut with dykes, and makes the coated steel appear to be solid
copper.

Trivia:
Dike = Diagonal Cutters
http://en.wikipedia.org/wiki/Diagonal_pliers
Dyke = Lesbian
http://en.wikipedia.org/wiki/Dyke_(lesbian)
Dyke or Dike = Earthen wall or dam
http://en.wikipedia.org/wiki/Dike_%28construction%29

Methinks "dikes" would be the correct spelling.

I have seen it written as dykes more often, but who knows?

Wikipedia knows best. If you mean't diagonal cutters, then the
correct term is "dikes".

Are you
saying lesbians can't cut wire? ;-)?

No. There are some questions that are best left unanswered. This is
probably one of those. I have no clue what dykes do in their spare
time. Not my style. However, please be advised that dikes are
suitable for doing more than just cutting wires. I use them for nail
clippers, wire strippers, sharpening pencils, opening packages, sewing
thread cutters, ty-wrap chompers, plastic handcuff removal, hole
punch, reamer, plant trimmer, and just about anything that requires
getting out of my chair and finding the proper tool.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Phil Allison]

"Richard Arse Licker Crowley"



** Gawd -

what a low life piece of autistic scum this human turd is.




..... Phil

[Michael A. Terrell]

Dave Platt wrote:

In article ,
Michael A. Terrell wrote:

You can slap RG- numbers on anything. It stopped being a military
standard a long time ago. Belden, Alpha, Times wire websites should
have some good white papers. RG meant 'Radio Guide', and all early coax
was braided copper shielding. Their is still some RF coax made this way,
but it uses teflon and silver plated copper and is VERY expensive.

http://www.belden.com/pdfs/Cable101/Shielding.pdf page 32 states 'Braid
is for low frequency, foil for high frequency'.

The RF-type foil-with-some-braid coax (LMR400 is one type) is quite
popular, and does seem to provide good shielding. However, there are
high-frequency (UHF/VHF) applications in which it has a rather evil
reputation. In particular, most repeater operators I know avoid it
like the plague when it comes time to run their primary feedlines.

Practical experience seems to suggest that this sort of construction
is prone to broadband-noise problems when used for duplex
applications... e.g. in a repeater where you're transmitting 25 - 100
watts up the cable in one direction, and also trying to receive a
microvolt-level signal on a nearby frequency at the same time in the
other direction.

The culprit seems to be the fact that the foil and braid don't make
perfect contact throughout the cable - they're not (and cannot be)
soldered together, and the contact between them is simply a
mechanical-pressure contact which is imperfect. There seems to be an
irregular make-and-break effect - I've heard it called "micro-arcing" -
which causes some small amount of the transmitted energy being
rectified and spread around the spectrum as broadband noise. Some of
this noise ends up on the repeater's receiver frequency, and cannot be
filtered out at the receiver... and this competes with the incoming
signal and can swamp it out (a form of receiver desensitization).

It doesn't take much of this noise to be a problem... I figured out
last year that in our repeater application (35 watt transmitter on
145.27 MHz) the transmitter is putting out literally a quadrillion
times more power than the receiver is picking up from a hand-held
radio out at the edge of our service area. Even a tiny fraction of
the transmitter power, rectified into noise, can wipe out the desired
signal.

The remedy for this, in practice, is to use a different type of
cable... one without the foil-and-braid shield construction. One
choice is a good "double braid" shield (which as Michael indicates,
tends to use a silver-plated braid). An even better choice is heliax,
which uses a seamless corrugated-copper shield.

Both are expensive - Andrew 1/2" heliax is edging up towards $3/foot
these days... and both are too stiff to use as microphone cable :-)

The foil-and-braid cables seem to be fine in simplex RF applications,
where you aren't trying to receive and transmit through the same cable
at the same time - the amount of broadband noise being generated is
inconsequential in simplex use.


50 ohm hardline is popular too. Some guys even make 50 to 75 ohm
matching networks and use surplus CATV trunkline.

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your account: http://www.usenettools.net/ISP.htm

[Michael A. Terrell]

Jeff Liebermann wrote:

On Sun, 04 May 2008 13:07:17 -0400, "Michael A. Terrell"
wrote:

Jeff Liebermann wrote:

On Sat, 03 May 2008 21:23:08 -0400, "Michael A. Terrell"
wrote:

Use a magnet, and see for yourself. The copper plating smears
when cut with dykes, and makes the coated steel appear to be solid
copper.

Trivia:
Dike = Diagonal Cutters
http://en.wikipedia.org/wiki/Diagonal_pliers
Dyke = Lesbian
http://en.wikipedia.org/wiki/Dyke_(lesbian)
Dyke or Dike = Earthen wall or dam
http://en.wikipedia.org/wiki/Dike_%28construction%29

Methinks "dikes" would be the correct spelling.

I have seen it written as dykes more often, but who knows?

Wikipedia knows best. If you mean't diagonal cutters, then the
correct term is "dikes".

Are you
saying lesbians can't cut wire? ;-)?

No. There are some questions that are best left unanswered. This is
probably one of those. I have no clue what dykes do in their spare
time. Not my style. However, please be advised that dikes are
suitable for doing more than just cutting wires. I use them for nail
clippers, wire strippers, sharpening pencils, opening packages, sewing
thread cutters, ty-wrap chompers, plastic handcuff removal, hole
punch, reamer, plant trimmer, and just about anything that requires
getting out of my chair and finding the proper tool.


Tinsnips?


--
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with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm

[Michael A. Terrell]

Jeff Liebermann wrote:

On Sun, 04 May 2008 11:11:40 -0400, "Michael A. Terrell"
wrote:

Chris S wrote:
If copper is soft then wouldn't that make it good for repeated
flexing in the sense that copper isn't so stiff that it wouldn't
split or crack?

Copper 'work hardens' when flexed. Over time it develops cracks, then
breaks. Stranded wire uses smaller conductors and has less problems per
conductor, due to a larger bending radius VS the diameter of the
conductor. The steel center conductor is meant for permanent
installation, but it holds up better on the bench that solid copper
coax.

Yep. Way back in the 1960's, I was installing 2way radios in various
vehicles. Someone found some RG-58/u, with a solid center conductor.
I was told to use it. About 100 vehicles later, someone declared that
solid coax was a bad idea. Management decided that it would replace
all the coax, but only after evidence of the first failure. So, we
waited, and waited, and waited. I was long gone when one of the coax
cables finally failed, about 5 years or 150,000 miles later.

Fast forward to the early 1990's and cellular telephone installs. At
the time, the average cell phone was big, boxy, heavy, and ugly. The
connector of fashion was the TNC. Once again, some dealers were
installing solid center conductor coax in the vehicles. They would
last about a month and then break. Huh? Solid center conductor
RG-58/u works in 100 buses for 5 years, but not in a passenger car for
a month? Something is obviously different.

It's the connector. In the 1960's we soldered everything. The common
PL-259 and UG-175 adapter was as sloppy a connection that could have
been mis-designed. 30 years later, everyone was crimping the
connectors. The breakage was always at the connector. The crimper
was dinging the center conductor. The sharp edge on the rear of the
center pin did the rest. Soldering the center pin and the longer
distance between the crimp and the point at which the cable will begin
to flex (UHF versus TNC) did much to prevent breakage.

All RG-6/u "type" cables are not all solid center conductor. Belden
Brilliance 1694F is flexible.
http://www.belden.com/pdfs/Prodbull/NP233.pdf
at about $0.70/ft. However, it cannot be used with Type-F connectors.
The data sheet mumbles:
"1694F is intended for use with connectors designed for 1694A"
which is not very helpful.

The foil outer shield usually tears in a flex test long before work
hardening does anything to the center conductor.


The early Raychem connectors didn't seem to have that problem, but we
used the 'F' to'G' adapters on the bench. I went through about a set of
cables a year while repairing CATV equipment, over 10,000 repaired items
and some were plugged in several times.


I've watched cable flex testers locally:
http://www.ideinc.com/plan_cycle.html
http://www.ideinc.com/plan_tester.html


We tested BNC, IDE, SMA, SMB, SMC, and several other connector types
of custom cables at Microdyne, prior to installing them in our products.


(Bring hearing protection). These simulate normal cable bending on
telephone headsets. The flexing is far more radical than anything
that would be encountered with RF coax cable. I asked if they had
ever tried flexing RF type coax cable. As I vaguely recall, neither
solid or stranded center conductor coax cables survived for very long,
but I don't recall the numbers. I'll ask.


The life depends a lot on the minimum bending radius. The smaller the
bend, the more either conductor is stressed. I always used cables that
didn't need tight bends, and long enough to let me flip an item on the
bench while repairing it.


Incidentally, there's also the tiny triboelectric noise created by the
mylar coated insulated shield, rubbing against the dielectric:
http://en.wikipedia.org/wiki/Triboelectric_effect
Good microphone cable should be "bonded" (i.e. glued) to prevent this
admittedly tiny noise problem. You're not going to find that in
commodity RF coax cable.


I never used coax for microphone cables, but I have lost count of the
number of 1000 foot spools of Belden two conductor microphone cable,
I've bought.


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[Michael A. Terrell]

Dead Paul wrote:

On Sun, 04 May 2008 15:17:37 +0000, Don Pearce wrote:

On Sun, 04 May 2008 11:15:45 -0400, "Michael A. Terrell"
wrote:

Dead Paul wrote:

no pickup inside coax.


Really? Then you don't know much about Coaxial cables, shielding
effectiveness, signal ingression and a dozen other topics. In other
words, no single shield is 100% effective.

And of course unless it is made of soft iron or mumetal, it doesn't shield
magnetically at all.

coax doesn't shield in that way. It works by cancellation and eddy current
effects duh!


DUH? That's the only part that you got right. If you believe that
crap, then explain how shielded cable allows RF into a microphone input.

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[Jeff Liebermann]

On Sun, 04 May 2008 21:22:47 -0400, "Michael A. Terrell"
wrote:

Are you
saying lesbians can't cut wire? ;-)?

Tinsnips?

That's the wrong tool and would really hurt. For such operations, I
suggest using the proper type of "dikes". See:
http://www.pbuh-traders.com/products/veterinary/castration_01.htm
Emasculator?

I don't use tinsnips. Too crude. I prefer aircraft snips.
Unfortunately, one really needs all various types (left hand, right
hand, offset LH, offset RH, straight, etc) aircraft snips.
http://www.skygeek.com/sheet-metal-tools.html
Invariably, the one I need is missing.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[krw[_3_]]

In article ,
says...

Jeff Liebermann wrote:

On Sun, 04 May 2008 13:07:17 -0400, "Michael A. Terrell"
wrote:

Jeff Liebermann wrote:

On Sat, 03 May 2008 21:23:08 -0400, "Michael A. Terrell"
wrote:

Use a magnet, and see for yourself. The copper plating smears
when cut with dykes, and makes the coated steel appear to be solid
copper.

Trivia:
Dike = Diagonal Cutters
http://en.wikipedia.org/wiki/Diagonal_pliers
Dyke = Lesbian
http://en.wikipedia.org/wiki/Dyke_(lesbian)
Dyke or Dike = Earthen wall or dam
http://en.wikipedia.org/wiki/Dike_%28construction%29

Methinks "dikes" would be the correct spelling.

I have seen it written as dykes more often, but who knows?

Wikipedia knows best. If you mean't diagonal cutters, then the
correct term is "dikes".

Are you
saying lesbians can't cut wire? ;-)?

No. There are some questions that are best left unanswered. This is
probably one of those. I have no clue what dykes do in their spare
time. Not my style. However, please be advised that dikes are
suitable for doing more than just cutting wires. I use them for nail
clippers, wire strippers, sharpening pencils, opening packages, sewing
thread cutters, ty-wrap chompers, plastic handcuff removal, hole
punch, reamer, plant trimmer, and just about anything that requires
getting out of my chair and finding the proper tool.


Tinsnips?

A dyke with tinsnips? Sounds dangerous.


--
Keith

[Michael A. Terrell]

Jeff Liebermann wrote:

On Sun, 04 May 2008 21:22:47 -0400, "Michael A. Terrell"
wrote:

Are you
saying lesbians can't cut wire? ;-)?

Tinsnips?

That's the wrong tool and would really hurt. For such operations, I
suggest using the proper type of "dikes". See:
http://www.pbuh-traders.com/products/veterinary/castration_01.htm
Emasculator?

I don't use tinsnips. Too crude. I prefer aircraft snips.
Unfortunately, one really needs all various types (left hand, right
hand, offset LH, offset RH, straight, etc) aircraft snips.
http://www.skygeek.com/sheet-metal-tools.html
Invariably, the one I need is missing.


I use them to cut up old cables, and large cable ties. It doesn't
matter which pair, as long as you can slip them between the bundle of
wire, and the cable tie. I leave an old pair of aviation snips under
the computer repair bench, along with some other metalworking hand tools
to strip computers that aren't worth fixing. I used to haul them out to
the shop, but it's easier to strip them, and pile their carcass by the
back door to make a single trip each day.


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[Michael A. Terrell]

krw wrote:

In article ,
says...

Tinsnips?

A dyke with tinsnips? Sounds dangerous.


Not as dangerous as Fred with an internet connection.


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[jim stewart]

It
came from a discount store as a TV coax extension cable.

Tee Hee white it will be with a couple of strands in the middle and no braid
worth talking about ...and a moulded plug at each end..........gosh you
techy guys will argue about anything! ......

[Earl Kiosterud]

"Dead Paul" wrote in message ...
On Sun, 04 May 2008 08:13:12 +0100, don pearce wrote:


Phil Allison wrote:
"Richard Crowley"
(1) Is it ok to use this sort of coax for a microphone?
Not enough details to answer your question adequately. First of all,
the kinds of microphones used for audio applications (reinforcement,
recording, etc.) are usually balanced and require cable with two inner
wires and an outside shield/screen. If you are trying to use a
balanced mic, then the cable is unsuitable because it is unbalanced.


** Not true at all !!

There is NO reason not to use a (suitable) co-axial type cable with a
microphone - either low or high impedance.

Despite all the nonsense you WILL have read elsewhere, co-axial cables
have as good or better rejection of external hum and noise sources as do
balanced twin wire cables.

Try it out if you don't believe this.


Of course a proper microphone cable is SCREENED balanced twisted pair, so
it enjoys the multiple benefits of electric screening by the outer, the
common mode nature of any residual interference and magnetic interference
cancellation by the twist in the balanced pair. A poorly screened coax
cable such as TV coax has only a part of the first of those so this claim
is clearly nonsensical. If it were true, professional microphone and mixer
companies would not be going to the trouble of designing balanced kit.



The length I need to use is 3 to 4 metres.
Not really important to the question. It wouldn't make much difference
if it were 1 m or 1Km


** If the mic is high impedance ( ie 50 kohms), then more than 10
metres or so of cable will cause high frequency response peaking and
early roll off as the cable capacitance loads the transformer inside the
mic.



If the mic is low impedance ( ie circa 250 ohms), then hundreds of
metres can be used - but not kilometres.



This is true.

d

Good quality coax will do the job if you don't mind the impedance mismatch
and if you want balanced line then you could use a pair of coax feeds in
parallel (impedance about 100 ohms for rg58). Also there's coax and
there's coax, I've seen rg58 like TV down-lead and others like shrunk down
UR67M.


--
___ _______ ___ ___ ___ __ ____
/ _ \/ __/ _ | / _ \ / _ \/ _ |/ / / / /
/ // / _// __ |/ // / / ___/ __ / /_/ / /__
/____/___/_/ |_/____/ /_/ /_/ |_\____/____/


Impedances are almost never matched, source to load, or source to transmission line to load
in audio. Telephone lines are the only case that comes to mind. Mics, speakers, preamps to
amps -- just not done. In short, we don't match source to cable, nor cable to load. Nor
source to load. Not only that, the impedance of a typical cable, such as rg-59, though 75
Ohms above 100KHz, is much much higher in the audio range.

Earl

[Earl Kiosterud]

"Michael A. Terrell" wrote in message
m...

Dead Paul wrote:

On Sun, 04 May 2008 15:17:37 +0000, Don Pearce wrote:

On Sun, 04 May 2008 11:15:45 -0400, "Michael A. Terrell"
wrote:

Dead Paul wrote:

no pickup inside coax.


Really? Then you don't know much about Coaxial cables, shielding
effectiveness, signal ingression and a dozen other topics. In other
words, no single shield is 100% effective.

And of course unless it is made of soft iron or mumetal, it doesn't shield
magnetically at all.

coax doesn't shield in that way. It works by cancellation and eddy current
effects duh!


DUH? That's the only part that you got right. If you believe that
crap, then explain how shielded cable allows RF into a microphone input.

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It's usually rf currents conducted through the shield conductor, through the guts of the
device being fed that cause the problem. It isn't rf across the input. A plain piece of
wire connected to the ground of the input can often still cause rf pickup. The cable's just
an antenna connected to the ground of the device. Shielding doesn't matter. I've seen it
in everything from little (amplified) computer speakers to pro audio mixers. The fix is
almost always to not allow the rf currents to flow through ground (or any) conductors in the
audio circuitry before they get to other external cables and such tied to the device at
other points in the circuitry. Tying the input and output cables, chassis, etc. to one
point is usually effective. Failing that, get each cable's ground (balanced or not) at
least straight to the chassis, if not one point -- but never to circuit paths inside the
unit where things like op-amps with huge open-loop gains can get all weird and demodulate
it. There's "pro" audio gear around (mixers, etc) with susceptibility to rf currents.

Earl

[Michael A. Terrell]

Earl Kiosterud wrote:

It's usually rf currents conducted through the shield conductor, through the guts of the
device being fed that cause the problem. It isn't rf across the input. A plain piece of
wire connected to the ground of the input can often still cause rf pickup. The cable's just
an antenna connected to the ground of the device. Shielding doesn't matter. I've seen it
in everything from little (amplified) computer speakers to pro audio mixers. The fix is
almost always to not allow the rf currents to flow through ground (or any) conductors in the
audio circuitry before they get to other external cables and such tied to the device at
other points in the circuitry. Tying the input and output cables, chassis, etc. to one
point is usually effective. Failing that, get each cable's ground (balanced or not) at
least straight to the chassis, if not one point -- but never to circuit paths inside the
unit where things like op-amps with huge open-loop gains can get all weird and demodulate
it. There's "pro" audio gear around (mixers, etc) with susceptibility to rf currents.


I was in the commercial sound business for over a decade, and never
had any of my installations pick up a radio, CB, or public service
radio. I am now disabled, but I was a broadcast engineer installing
audio equipment in some of the worst environments possible At one site
I had to drive a ground rod over 80 feet, through Alaska's permafrost to
get a better ground. I had the AM BCB transmitter's signal riding on
every 'ground' in the complex. You could even see it in the video
baseband of the TV station at that site. I removed a couple miles of
substandard, and excess cabling to clean up that mess. Some 'engineer'
had paralleled the two audio boards at one time, then left the cables
hooked to one of the boards after some upgrade. It was really crappy two
conductor, tinned braid, no jacket garbage that was so corroded that the
shield was useless. If the radio station's audio console hadn't been
the original 1948 Gates, with transformer input, the station would have
been useless.

Any 'pro' gear that is susceptible to RF problems is nothing more
than over hyped consumer crap. A two hole ferrite bead, and a 100 pF
disk capacitor made a decent low pass filter for non transformer
balanced inputs. Any equipment with unbalanced inputs is just consumer
crap, no matter what you pay for it.

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