OK to use TV coax for microphone?

OK to use TV coax for microphone?

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]

Re: OK to use TV coax for microphone?

On Sat, 03 May 2008 10:58:27 +0100, Chris Siz
<default@default.invalid> 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?

If you can get hold of some better cable do so. You have two problems
here - first coax isn't balanced, which is sort of bad news for tiny
signals such as you get from a mic. And secondly, to compound that, if
you strip back a little of the outer sheath, you will find that the
screen is 90% holes - in other words, the cable is just about
unscreened.

As for using it for UHF TV, go ahead - that is what it is meant for,
and 10 meters is just about the maximum run length before you need to
think about using something better.

d

--
Pearce Consulting
* w w w .pearce.uk . com

Re: OK to use TV coax for microphone?

On Sat 03 May 2008 11:10:02, Don Pearce wrote:

> On Sat, 03 May 2008 10:58:27 +0100, Chris Siz
> <default@default.invalid> 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?
>
> If you can get hold of some better cable do so. You have two
> problems here - first coax isn't balanced, which is sort of bad
> news for tiny signals such as you get from a mic. And secondly, to
> compound that, if you strip back a little of the outer sheath, you
> will find that the screen is 90% holes - in other words, the cable
> is just about unscreened.
>

Um, yes. It is exactly like that. I had thought maybe they were using
very thin wires and that way getting a reasonable amount of physcial
screening but the wires I found were so sparse that it must be more
like what you describe!

> As for using it for UHF TV, go ahead - that is what it is meant
> for, and 10 meters is just about the maximum run length before you
> need to think about using something better.
>
> d
>

Re: OK to use TV coax for microphone?

In message <Xns9A936FA2EF13F451E7A@127.0.0.1>, Chris Siz
<default@default.invalid> writes
>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?
>
>
While you might get away with using your cable, good screening/shielding
becomes increasing important at the lower frequencies, as the
interfering signals (on the outside of the coax) penetrate more easily
through the outer shield. Well-screened audio would be better. In many
cases, 'flimsy' screening may be adequate at UHF (and the cable may have
low loss) but, again, well-screened cable will be better for preventing
interference. Maybe it's a case of try it and see what happens?
--
Ian

Re: OK to use TV coax for microphone?


"Ian Jackson" <ianREMOVETHISjackson@g3ohx.demon.co.uk> wrote in message
news:6LMYsOWpwDHIFwVF@g3ohx.demon.co.uk...
> In message <Xns9A936FA2EF13F451E7A@127.0.0.1>, Chris Siz
> <default@default.invalid> writes
> >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?
> >
> >
> While you might get away with using your cable, good screening/shielding
> becomes increasing important at the lower frequencies, as the
> interfering signals (on the outside of the coax) penetrate more easily
> through the outer shield. Well-screened audio would be better. In many
> cases, 'flimsy' screening may be adequate at UHF (and the cable may have
> low loss) but, again, well-screened cable will be better for preventing
> interference. Maybe it's a case of try it and see what happens?

I would have thought the converse to be true, surely the "holes" in the
screening
braid would be less of a problem at audio frequencies than at UHF?
I am thinking in terms of wavelength.

Re: OK to use TV coax for microphone?

Theo wrote:
> "Ian Jackson" <ianREMOVETHISjackson@g3ohx.demon.co.uk> wrote in message
> news:6LMYsOWpwDHIFwVF@g3ohx.demon.co.uk...
>> In message <Xns9A936FA2EF13F451E7A@127.0.0.1>, Chris Siz
>> <default@default.invalid> writes
>>> 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?
>>>
>>>
>> While you might get away with using your cable, good screening/shielding
>> becomes increasing important at the lower frequencies, as the
>> interfering signals (on the outside of the coax) penetrate more easily
>> through the outer shield. Well-screened audio would be better. In many
>> cases, 'flimsy' screening may be adequate at UHF (and the cable may have
>> low loss) but, again, well-screened cable will be better for preventing
>> interference. Maybe it's a case of try it and see what happens?
>
> I would have thought the converse to be true, surely the "holes" in the
> screening
> braid would be less of a problem at audio frequencies than at UHF?
> I am thinking in terms of wavelength.
>
>

Same here. *shrug* ?

Re: OK to use TV coax for microphone?


"Chris Siz" <default@default.invalid> wrote in message
news:Xns9A936FA2EF13F451E7A@127.0.0.1...
> 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?
>

Yes, it's OK to use coax for a mic cable assuming the mic is a single ended
connection (one wire) with ground. The biggest issue is the cable
capacitance. Depending on the mic's impedance, this capacitance will
attenuate high frequencies. A low impedance mike will work better than a
high impedance mic. The accumulated capacitance in four meters of cable will
be a couple of hundred pico-farads, probably not a problem.

For UHF TV cables are usually 72 ohms. If your cable is 72 ohms, it's
probably OK. If it is 50 ohms it will still work but may degrade the picture
quality because of reflections within the cable. Try and see. If the antenna
is 300 ohms, the cable is not suitable unless matched with a balun or other
impedance matching device.

Re: OK to use TV coax for microphone?

In message <S7_Sj.2243$506.1543@newssvr27.news.prodigy . net >, Bob Eld
<nsmontassoc@yahoo . com > writes
>
>"Chris Siz" <default@default.invalid> wrote in message
>news:Xns9A936FA2EF13F451E7A@127.0.0.1...
>> 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?
>>
>
>Yes, it's OK to use coax for a mic cable assuming the mic is a single ended
>connection (one wire) with ground. The biggest issue is the cable
>capacitance. Depending on the mic's impedance, this capacitance will
>attenuate high frequencies. A low impedance mike will work better than a
>high impedance mic. The accumulated capacitance in four meters of cable will
>be a couple of hundred pico-farads, probably not a problem.

Out of interest, how does the capacitance of ordinary TV coax (which
will be 75 ohms, of course) compare with 'proper' mic cable? Of course,
a lot of audio is balanced (usually nominally 600 ohms), which makes
things generally less prone to the pick-up of interference. Unbalanced
connections via coax (even if proper screened audio cable) is
less-tolerant.
>
>For UHF TV cables are usually 72 ohms. If your cable is 72 ohms, it's
>probably OK. If it is 50 ohms it will still work but may degrade the picture
>quality because of reflections within the cable.
>Try and see.

As it's TV coax, it's unlikely to be 50 ohms.

>If the antenna
>is 300 ohms, the cable is not suitable unless matched with a balun or other
>impedance matching device.

UK aerials are not 300 ohms (except for those indoor FM radio aerials
made from 300 twin feeder). I believe that, these days, they are also a
bit of rarity in the USA.
--
Ian

Re: OK to use TV coax for microphone?

On Sat, 3 May 2008 17:01:19 +0100, in sci.electronics.design Ian
Jackson <ianREMOVETHISjackson@g3ohx.demon.co.uk> wrote:

>
>Out of interest, how does the capacitance of ordinary TV coax (which
>will be 75 ohms, of course) compare with 'proper' mic cable? Of course,
>a lot of audio is balanced (usually nominally 600 ohms), which makes
>things generally less prone to the pick-up of interference. Unbalanced
>connections via coax (even if proper screened audio cable) is
>less-tolerant.

600 ohms is dead and buried, for the audio world.The only time it is
mentioned is in data sheets, "will drive XXdB into 600R" etc


martin

Re: OK to use TV coax for microphone?


"Martin Griffith" <mart_in_medina@yah00 . es > wrote in message
news:sh9p14hjdd2992avksh5uaiuhnset5vnek@4ax . com ...
> On Sat, 3 May 2008 17:01:19 +0100, in sci.electronics.design Ian
> Jackson <ianREMOVETHISjackson@g3ohx.demon.co.uk> wrote:
>>
> 600 ohms is dead and buried, for the audio world.The only time it is
> mentioned is in data sheets, "will drive XXdB into 600R" etc
>
>
> martin

Quite so. The concept of matching a microphone's impedance to get the best
power transfer has not been practiced for a considerable time.
Modern dynamic mics expect to look at a "bridging" impedance e.g. around 10K
for a mic having a Z of 150-200 Ohms and to operate as a voltage, rather
than a power source.
The characteristic imedance of the feeder (over a few feet) may thus be
disregarded.


Les.

Re: OK to use TV coax for microphone?

Les. wrote:
> "Martin Griffith" <mart in medina@yah00 . es > wrote in message
> news:sh9p14hjdd2992avksh5uaiuhnset5vnek@4ax . com ...
>> On Sat, 3 May 2008 17:01:19 +0100, in sci.electronics.design Ian
>> Jackson <ianREMOVETHISjackson@g3ohx.demon.co.uk> wrote:
>> 600 ohms is dead and buried, for the audio world.The only time it is
>> mentioned is in data sheets, "will drive XXdB into 600R" etc
>>
>>
>> martin
>
> Quite so. The concept of matching a microphone's impedance to get the best
> power transfer has not been practiced for a considerable time.
> Modern dynamic mics expect to look at a "bridging" impedance e.g. around 10K
> for a mic having a Z of 150-200 Ohms and to operate as a voltage, rather
> than a power source.

No they expect to see 1K2 to 2K not 10K and that is what most pro mic
pres provide. 10K input impedance is for bridging line levels.

Cheers

Ian

Re: OK to use TV coax for microphone?


"Ian Thompson-Bell" <ruffrecords@yahoo.co.uk> wrote in message
news:fvik1n$29jf$1@energise.enta . net ...
> No they expect to see 1K2 to 2K not 10K and that is what most pro mic pres
> provide. 10K input impedance is for bridging line levels.
>
> Cheers
>
> Ian

Er, not in every case. In any case my point about the mic being regarded as
a voltage source remains true.

For speech use (3K) you can get away with just about anything!

Les.

Re: OK to use TV coax for microphone?

On May 3, 4:58 am, Chris Siz <defa...@default.invalid> 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?
>
> --
>
> [x-posted to 3 relevant groups]

Isn't coax kind of rigid? Will the microphone need to move around?

Re: OK to use TV coax for microphone?

On Sat 03 May 2008 15:54:24, wrote:

> On May 3, 4:58 am, Chris Siz <defa...@default.invalid> 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?
>>
>> --
>>
>> [x-posted to 3 relevant groups]
>
> Isn't coax kind of rigid? Will the microphone need to move around?

This cheapo coax is quite flexible. It may an indication of poor
physical resistance to squashing and also of limited copper content.

Re: OK to use TV coax for microphone?

In article <Xns9A936FA2EF13F451E7A@127.0.0.1>,
Chris Siz <default@default.invalid> 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.

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