[1000mp] isolation transformers and SuperCable

Sat, 22 Jun 2002 07:16:24 -0500

Tom, I do use the isolation transformers.
I just didn't mention them as they weren't in the circuit at the time as I
had something wrong and when I had them in the signal to the soundcard was
attenuated too much.

I also said I had a ground at each end of the cable. I do but I only use one
end.
I put a ground strap at each end to see if one end or the other was better.
Jury is still out on that. So far I can't see any difference.

I have two questions for you.
Seeing as how my friend Kok Chen, W7AY, (used to be AA6TY) says your even
more picky about engineering that he is, I'll ask your opinion.

Should the ground for the cable be at the rig end or the computer end.
Should the isolation transformer be a the rig end or the computer end.

And something I don't understand.
I've been plagued with 'line noise' for a long time.
I can't really tell if it's com ed line noise or cable TV leakage as my
little portable radio tuned off a station detector takes me to the power
pole  but doesn't clue me as to what on the pole is the culprit.

But since I built my cable, my noise level is WAY down. I mean drastically.
Could be coincidence but I'm getting suspicious.
I never suspected computer hash as I had the noise with the computer turned
off.
I do have a few crt monitor birdies, I can turn the monitors off and cure
that.
Could the cable block the noise I was hearing previously? I'm pretty sure it
was line noise as a heavy rain would quiet it down for a few days and then
it would resume.
But it's been hot and dry for a week and since I installed the cable it's
been S0 noise in the radio.
I surely didn't expect that.

Thanks for your time. I'm always open to suggestions.

----- Original Message -----
From: "Tom Rauch" <[email protected]>
To: <[email protected]>
Sent: Friday, June 21, 2002 11:31 PM
Subject: Re: [1000mp] isolation transformers and SuperCable

> > Bill, typical audio isolation transformers (e.g. Stancor TTPC) have
> > less than 2dB of loss.  I've never noticed any loss in level when
> > using Stancor or Radio Shack transformers between the MP's rear audio
> > connectors and various SoundBlaster cards.
>
> My station is full of isolation transformers on the headphone lines,
> since I have multiple receivers and transceivers and an audio buss
> that ties any audio output to any listening position. Even a 4 inch
> wide thick copper flashing is NOT low enough ground resistance to
> prevent audio hum from ground loops. Without the audio transformers I
> can even hear the hum from my tower lights blinking in the
> headphones, and see it on the computer spectrum display or hear it
> when I play back digital recordings. All of this in spite of the fact
> my station is very well grounded.
>
> Because of that, my sound card has additional isolation transformers.
> They are mounted on a PC board hanging from the soundcard aux input
> plug on the computer. That way I NEVER need to ground a shield at
> both ends. As someone else pointed out, grounding the shield of an
> audio line at both ends is just begging for problems.
>
> I use transformers from Mouser, and loss in them is negligible.
>
> By the way, some symptoms that appear to be RF ingress are really not
> due to RF. They are actually from power supply currents that vary at
> an audio rate as the current in the PA stages changes, as that
> current causes a drop across audio cables that are grounded at both
> ends.73, Tom W8JI
> [email protected]
>
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