[sdiy] non shield cable

[Czech Martin]

Like all things in life, this depends.
It depends on your environmental situation.
Giving a general answer would perhaps simply end
as an endless/pointless e-mail debate.

There are areas with very high E and H fields,
like obviously my flat 8-<.
I see FM radio, 50 Hz and harmonics, and 16 2/3 Hz
and harmonics (railway 40 m away).
And of course my computer monitor with ~70 Hz
plus harmonics and ~ 17kHz plus harmonics.
And some higher pitched stuff radiation from some
ribbon data cable...
In my room the oscilloscope (1M impedance) 
shows 20-40mV pp noise if I stick a 5cm aluminum
ball to the probe tip.
I think the electric field can be computed from this.

And there may be other areas (rural) which are quite
clean in this respect.

It also depends on input/output impedances.
If output impedances are low the magnetic coupling
will be more prominent. In the other case the
electric field stuff will show more.
This is why a guitar amp input (arround 1Meg)
will certainly only work with shielded cable.
(guitar has not such a low amplitude, at least the way
I slam it ;->)


The next thing it depends on is your ears.
How much noise do you tolerate?

And then it depends on the application.
Example: my VCR will have some 16kHz speakthrough
to the audio jacks. If I want to record a sample
from TV, it is at first no problem in most situations.
But if this sample is processed by pitch shifting, modulation processes
etc etc. the noise can no longer be tolerated. It gets very prominent.
In this case I can not change the "antenna" situation,
so I have to clean up the sample with a sharp FIR notch
filter I programmed for this purpose.

Another problem is that noise above 20kHz or so can disturb
some older A/D converter gear. Some old DAT machines,
or portable DAT machines have no oversampling, so the
high pitched noise will appear as nasty alias...

Of course, cleaning up is always 2nd choice, and works
only for narrow band noise.


So , if you or your system are/is picky and if you want that your system
runs clean under all situations (moving house),
shielded cable has some point.

Oh, you can do it the other way as well:

Use unshielded wire, and shield you room.
Wire netting material should do the trick
up to several MHz, but not for low freq. H fields.

Yes, I'm very picky about noise.

m.c.



> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Fernando de
> Izuzquiza
> Sent: Mittwoch, 8. Oktober 2003 23:50
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] non shield cable
> 
> 
> Hi all,
> 
> Wondering about risks of using non-shielded cable for patching.
> Crosstalk? EMI? RFI?, where is the "danger"?
> Planning to use 4mm banana cabling but not shure of potential 
> problems,
> mostly for audio signals but also for CV.
> 
> Imagine a 3 or 4 rack frames modular, each 12U, so lots of 
> modules. Heavily
> patched. Cords interpatching frames too. One PSU per frame at 
> about 1 meter
> away in the floor.
> What happens if all cables are 4mm banana patchcords? (except 
> output cables
> to amps)
> 
> How much will the audio and CV signals suffer, degrade or be prone to
> interference, etc?
> 
> 
> Thank you,
> 
> Fernando
> 
> 
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