EMRFD Message Archive 5589

Message Date From Subject
5589 2010-12-28 00:25:09 ae5ew EMRFD Book
Well,I went through all of it. Spent several hours reading parts of it. There certainly is a wealth of information provided. I was hoping to see a 2m and/or 70cm down converter. The DSP10 looked interesting for weak signal 2m work. I have an excellent receiver which I would like to put to use receiving 2m and 70cm signals. Even the aircraft band would be interesting. For me, for a while at least.
I need to order two shielded audio transformers for my psk31 work. Not certain I actually need them. Also need to order some grounding braid. Better coax would be nice as well. Not certain I will be operating portable any time soon with home built gear.
Charles AE5EW
5590 2010-12-28 05:23:34 Tim Re: EMRFD Book
IME you don't have to buy a special interface to have fun with PSK31. Hook up the audio from the rig to your PC soundcard any which way, start up some freeware (Digipan is really easy under Windows... kpsk under Linux), and start listening and decoding. After that you hook up the audio the other directi
5591 2010-12-28 07:54:04 kb1gmx Re: EMRFD Book
My regular interface uses a few transformers salvaged from a
couple of old pc modem cards. Just hot glued them into a bax woth pots and coupling caps and tada works. The keying line I put the
opto isolator ina large cable hood with the connector with a pigtail coming out it's enough for a few of my rigs and my PSK20 uses vox
so that is simpler.

I started by using Digipan on an old 486 laptop using a small mic near the speaker to rx and holding the mic near the PC speaker.
Awkward but, it worked.


5592 2010-12-28 08:49:15 Andy Re: EMRFD Book
> Regarding PSK31... those transformers are often specced to be
> there because someone had troubles with ground loops or
> common-mode computer noise. These are not universal problems
> but if you do decide you need transformers, rather than order some
> fancy-pants transformers most people do just fine with Radio Shack
> part number 273-1380 and 273-1374. IMHO the best fun comes
> not from ordering all the fancy-pants special components but by
> tacking together stuff already in the junkbox :-).

Indeed, some people do just fine with the transformers they already
have in their shack: the loudspeaker and microphone. Acoustic
coupling, even across the room, is supposed to work pretty well for

Another source for cheap audio transformers is discarded computer modems.

I don't recall *shielded* transformers being required for amateur
radio rig/soundcard interfaces.

Somewhere (and I can never find it when I want to), there is an
excellent webpage by an expert on audio grounding, who advocates not
using transformers, because it is USUALLY possible to fix a "grounding
problem", by fixing the problem, not by adding band-aid fixes like
transformers. It can be done. (After all, you probably didn't add
transformers between your CD player or tape deck and your stereo

There are some rigs that have unusual inputs or outputs, such as
balanced outputs, that do require transformers to do it right. But
these are in the minority.

5593 2010-12-28 09:26:28 ae5ew Re: EMRFD Book
I would certainly like to read that paper should you find it.
My current setup is direct wired from the PC to the FT-950. I noticed some odd signals when analyzing the audio channel with some of those free 'audio scopes'. The signals weren't there when the cable was disconnected at the rig end. One was around 10khz, well outside the audio bandwidth of the FT-950. Some appeared to be harmonics of 60hz. 120, 180. They weren't very strong. Also, I have asked for reports of my signal and have been told 'everything looks good'. No splash, etc. I have seen some terrible splash from stations in Cuba. They might as well as have been running full SSB. The primary reas
5595 2010-12-28 10:06:14 Mike Mayer Re: EMRFD Book

This might be the paper you are referring to:


Check the publications page as well. There are other papers that might be of


Mike Mayer

-----Original Message-----
5596 2010-12-28 11:45:42 ae5ew Re: EMRFD Book
I already have that one. It deals mainly with EMI/RFI.
Charles AE5EW

5597 2010-12-28 12:15:43 Mike Mayer Re: EMRFD Book
This presentation looks like it is more specifically about audio connections
to/from computers:


Mike Mayer

-----Original Message-----
5598 2010-12-28 12:44:52 ae5ew Re: EMRFD Book
That is at least one source. I must say, 'they don't use single point grounds as they should'. Or at least, what I have seen for safety. Equipment to equipment grounds are not advised.
Back to the audio discussion. Long distance audio runs should run balanced. If the ends are unbalanced, then use an audio transformer at BOTH ends of each line with something like CAT5/6 cabling. They have great twisted pairs. Ma Bell ran 600 ohm twisted pair, balanced lines in phone wiring for many decades. CAT5/6 cabling is even better than what Ma Bell used/uses. Ok, on to finish reading the article. Be back shortly.
Charles AE5EW

5599 2010-12-28 12:56:17 ae5ew Re: EMRFD Book
I should have said 'use shielded audio transformers'. This will help prevent power supply transformers from affecting the audio transformer. Transformers will 'talk' to each other if you let them.
Charles AE5EW

5602 2010-12-28 21:47:03 Andy Re: EMRFD Book
> 'they don't use single point grounds as they should'. Or at least, what
> I have seen for safety. Equipment to equipment grounds are not advised.

But what you have is basically an audio interconnection problem, just
like the one in your stereo system. All those cables with RCA plugs
that run between the components of a stereo system, are multiple
equipment-to-equipment grounds. It's OK to do it in a stereo system,
isn't it?

But don't use the equipment-to-equipment connections to replace a low
resistance connection back to the system ground point.

> Long distance audio runs should run balanced.

Yes. Whenever the distances are so long that a ground difference is
unavoidable, balanced is the way to do it. Or fiber, nowadays. Take
the ground out of the equation.

Within a room, where both pieces of equipment can be put on the same
power feed, I think Jim Brown is saying that you don't need to do

5728 2011-01-14 00:46:59 longjohn119 Re: EMRFD Book
If you have a pro soundcard (mono NOT stereo inputs) then you can use this perfectly wicked looking little circuit, the biggest drawback is you need a true split supply for the op amp but it kills ground loops on unblanced inputs better than anything. Those of you who use Behringer signal processing gear probably have outputs like this but didn't know it. I have these on the outputs of my SDR receivers because you can't find flat from near DC to 50-100Khz (even wider with a 192Khz sampling soundcard) transformers without hocking the farm.


Circuit 5a, I use 3.3K for the bridge resistors (Best compromise for optimum input noise impedance for a 5532/4 and load on preceding stages) and 100 ohms for the Rs resistors. 3.0K will work well too

Although designed for single ended inputs it will also work with true balanced and impedance balanced (Like the Delta 44/66/1010) inputs with little penalty and if you use a regular single conductor cable all you lose is the ground cancellation which is what you had in the 1st place. That's why it's become so popular with pro audio manufacturers, if it has 1/4" tip-ring-sleeve 'balanced' outputs chances are this is the output circuit used because it works so well for chaining together devices with their own power supplies and common grounds without a massive hum/ground problem. I've been using this circuit for over 20 years but it's become really popular in the last 10-15 years with audio equipment designers.