03-21-2012, 02:05 PM
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W9WDX Amateur Radio Club Member
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Join Date: Jun 2010
Got my Sound card this Afternoon installed it hooked the Icom to it went on 10m did a quick PSK31 test and it works no feedback issues with TX.
Originally Posted by W5LZ
That isolation is a bigger biggy than you might think, it can get really aggravating (radios and computers do not like each other much). And one way of doing that isolating is by means of a transformer to handle any impedance differences between that radio's output and the sound card's input. Two birds, one stone. Sometimes that transformer isn't quite a enough, and if so, adding a 0.001 or 0.01 ceramic capacitor in the 'hot' line at the transformer tames it a bit more. The same basic thing is applicable for the line from that sound card's output to the radio's audio input (isolation).
One thing that can creep up on you is the difference in ground potential between radio and computer. That amounts to where you happen to find a common ground with the computer. The 'ground' of that sound card's cable is seldom if ever the computer's chassis ground, that sound card 'floats' above ground. Have you ever connected the sound card's ground to chassis ground and had the computer die/turn off? That's a scary occasion! Not sure if it's still true of the newer computers, and I don't plan to find out. Much simpler to just do it right to start with.
Controlling the audio levels in/out of both the computer and radio can get really aggravating too. It can be done, but usually means adjusting volumes when you so SSTV (or other modes using the sound card) by the SSTV'er. Just remember to readjust those levels when you're finished so that 'normal' sound card operation is restored. Remember that 'aggravating' thingy, just more of it. OR, just get an interface that does all that by it's self, if you don't wanna make one, or are too lazy to do all that adjusting stuff (--> ME). they also are nice because they take care of doing all the connections/connector finding and installing much easier. That makes it sound like I think you should get an interface, but that's really not what I'm saying. Doing it all your self is very nice and certainly possible! If you don't need all those 'refinements', or 'extras', for your particular equipment then good!
And the same old warning again, this crap really get's addicting...
And while I'm thinking about it, that interface (store bought or home made) will usually work for any mode that uses the sound card, not just SSTV.