[RTTY] RTTY SO2R "leakage"?

[Jim Hargrave]

FYI: Sound  card recommendation.

I am having excellent results with a Behringer UCA-222 (USB). 
It has Stereo Line in & line out (RCA) connections. 

73, Jim - w5ifp at gvtc.com

>> -----Original Message-----
>> From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of
>> David G3YYD
>> Sent: Saturday, September 5, 2015 6:01 AM
>> To: rtty at contesting.com
>> Subject: Re: [RTTY] RTTY SO2R "leakage"?
>> 
>> Tim
>> 
>> The amplitude range that 2Tone will work over is enormous. It
>> samples at 48KHz at 16 bits and decimates that to a low sample
rate.
>> This alone increases the 90dB of the sound card by 30dB. Then
>> there is the 45.45Hz filter bandwidth as well adding additional
10s of
>> dB.
>> 
>> A small amount of cross talk could easily result in a decode. If
it
>> bothers you then make sure the leads going to each radio are well
>> screened and correctly terminated at the radio plug end and run
>> individual leads from each radio to the plug that goes into the
PC.
>> However the crosstalk is most likely to be internal to the
PC/laptop.
>> If you are using a cheap $5 sound card then buy another around
$25
>> or so. I tested a $5 one here and threw it in the bin! Its
performance
>> was terrible in virtually all aspects.
>> 
>> I looked up the spec for a chip used in a good quality sound card
and
>> its cross talk for the A/D converter was 90dB. That would be for
an
>> optimally designed PCB. However I would think most PCBs are non-
>> optimal so it will be worse than that.
>> 
>> If it really bothers you then the answer is simple set the radios
to
>> use different tone sets. 2Tone has unlike MMTTY the ability to
use
>> the sound card with left or right channel for TX so that the RX
and
>> TX tone frequencies for the each radio will be correct.
>> 
>> 73 David G3YYD
>> 
>> -----Original Message-----
>> From: RTTY [mailto:rtty-bounces at contesting.com] On Behalf Of
>> Tim Shoppa
>> Sent: 04 September 2015 16:47
>> To: rtty at contesting.com
>> Subject: [RTTY] RTTY SO2R "leakage"?
>> 
>> I am a bit mystified by some observed behavior in my SO2R RTTY
>> setup.
>> 
>> I feed the left radio into the left audio channel, and feed the
right
>> radio into the right audio channel.
>> 
>> I have one MMTTY and one 2Tone per radio, each set up to only
>> look at the appropriate left or right audio channel.
>> 
>> Doing this all in SO2R seems to work. But every so often a really
>> loud signal on radio 1, will be decoded and printed in the
decoder
>> for radio 2, especially if the signal on radio 1 is pinning the
S-meter
>> and radio 2 is looking at a signal in the noise. Same things
happen
>> with 1 and 2 reverse.
>> 
>> The first time this happened I was stumped, but then figured out
>> that I had left a microphone plugged in to the sound card at same
>> time. Audio was escaping from my headphone, finding its way to
>> the microphone, and then being fed into both channels! (Evidently
>> microphones are treated as mono
>> devices.)
>> 
>> But now I have the microphone unplugged, and still the leakage is
>> still continuing at a lower level. I don't see any signs of
decoder
>> leakage in the decoders' waterfalls when just looking at band
noise
>> and regular signals but we all know in a contest there are some
>> really loud signals.
>> I'm trying to figure out if this "leakage" between channels is in
my
>> PC hardware, in the audio cabling, or in the windows driver,
maybe
>> a microphonic effect in the PC case, or some common coupling
>> through ground or a power supply, or what. Or maybe there is
>> some AGC function being applied by the sound card ADC in
>> response to a loud signal, such that a loud signal on one channel
>> shows up very weakly in the other channel. Any advice on tracking
>> this down?
>> 
>> Tim N3QE
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