Re: OK to use TV coax for microphone?

On Sun, 04 May 2008 12:41:01 +0100, Chris Siz
<default@[EMAIL PROTECTED]
> wrote:

>On Sat 03 May 2008 19:05:41, Kevin McMurtrie wrote:
>
>> In article <Xns9A936FA2EF13F451E7A@[EMAIL PROTECTED]
>,
>>  Chris Siz <default@[EMAIL PROTECTED]
> 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?

He thinks he is earnest.  Most of these effects do occur in some
applications.  If you have read the whole thread you will have seen
even more other use case issues.  Not all of which apply to your use.
Kevin's biggest problem is that he does not know what the boundaries
of applicability are of the various things he thinks he understands.

In general, it will work OK for low fidelity / casual use.  It will
not work well, and it may be a reliability problem.  Forget about it
for good amateur or serious use.