On Tue, 01 Dec 2009 13:00:49 GMT, (Don Pearce) wrote:

On Tue, 01 Dec 2009 10:32:20 +0000 (GMT), Jim Lesurf
wrote:

In article , Ian Bell
wrote:
Dave Plowman (News) wrote:
In article , Ian Bell
wrote:
I need to send an audio signal from a 50K ohm source over a distance
of a couple of feet in a screened cable. However, most audio coax
seems to be about 100pF/ft so 2ft of this and 50K will turn over
just below 16KHz. So, anyone know a source of low capacitance audio
coax?

Those sort of output impedances were common in valve days. Use a video
or RF coax to your requirements. Maplin sell a range by the metre.


I keep forgetting about Maplin. I checked their catalogue and they have
an AV coax by Shark that is only 65pF/metre.

I've been trying to recall the type of the UHF cable I've tended to use for
general purpose audio coax. I bought a drum 25 years ago because it was
c60pF/m and worked OK. Single solid inner, foamed spaced, sparce braid
outer. Fairly high diameter but works nicely for long runs. I'd recommend
it if I could remember the type number! :-)

Slainte,

Jim

RG63 comes in at 10pF per foot; it's an air-spaced polyethylene, so
well suited to an installation like this.

d

Forgot - useful chart he

http://www.rfcafe.com/references/ele...coax-chart.htm

d