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A second radio's feed into a 'Y' cable is seldom going to do much good. As already stated, the potential for a ground loop is one problem with that. Another is that sound card "grounds" are very seldom actually at ground potential, they are almost always above ground by a few volts (they 'float'). Which means that if the sound card's ground is grounded to the computer's chassis, it causes a 'turn off' of the computer (shorts the sound card). That can happen if the computer and radio's are both grounded to the same station ground. One of the things a typical interface does is eliminate that possibility.
If you can disconnect one radio, only connect one at a time, that can get rid of that hum, probably. Why both connected at the same time?
I've got a 'work around' for that multiple sound card thingy, it's a USB sound card. Of course that introduces other complications, another driver for that sound card, and a USB hub (in my case, lot's of USB ports, 128 of them are possible!). Why do it that way? It was cheap, $20 for a sound card, no slot required in the computer. The sound card in the computer only does things for the computer, the external one(s) handle radio stuff. I can't say that's -the- way to do it, it just works out handier/easier for me.
- 'Doc

<blockquote data-quote="W5LZ" data-source="post: 367232" data-attributes="member: 129">A second radio&#039;s feed into a &#039;Y&#039; cable is seldom going to do much good.&nbsp; As already stated, the potential for a ground loop is one problem with that.&nbsp; Another is that sound card &quot;grounds&quot; are very seldom actually at ground potential, they are almost always above ground by a few volts (they &#039;float&#039;).&nbsp; Which means that if the sound card&#039;s ground is grounded to the computer&#039;s chassis, it causes a &#039;turn off&#039; of the computer (shorts the sound card).&nbsp; That can happen if the computer and radio&#039;s are both grounded to the same station ground.&nbsp; One of the things a typical interface does is eliminate that possibility.If you can disconnect one radio, only connect one at a time, that can get rid of that hum, probably.&nbsp; Why both connected at the same time?I&#039;ve got a &#039;work around&#039; for that multiple sound card thingy, it&#039;s a USB sound card.&nbsp; Of course that introduces other complications, another driver for that sound card, and a USB hub (in my case, lot&#039;s of USB ports, 128 of them are possible!).&nbsp; Why do it that way?&nbsp; It was cheap, $20 for a sound card, no slot required in the computer.&nbsp; The sound card in the computer only does things for the computer, the external one(s) handle radio stuff.&nbsp; I can&#039;t say that&#039;s -the- way to do it, it just works out handier/easier for me.&nbsp;- &#039;Doc</blockquote>

[QUOTE="W5LZ, post: 367232, member: 129"] A second radio's feed into a 'Y' cable is seldom going to do much good. As already stated, the potential for a ground loop is one problem with that. Another is that sound card "grounds" are very seldom actually at ground potential, they are almost always above ground by a few volts (they 'float'). Which means that if the sound card's ground is grounded to the computer's chassis, it causes a 'turn off' of the computer (shorts the sound card). That can happen if the computer and radio's are both grounded to the same station ground. One of the things a typical interface does is eliminate that possibility. If you can disconnect one radio, only connect one at a time, that can get rid of that hum, probably. Why both connected at the same time? I've got a 'work around' for that multiple sound card thingy, it's a USB sound card. Of course that introduces other complications, another driver for that sound card, and a USB hub (in my case, lot's of USB ports, 128 of them are possible!). Why do it that way? It was cheap, $20 for a sound card, no slot required in the computer. The sound card in the computer only does things for the computer, the external one(s) handle radio stuff. I can't say that's -the- way to do it, it just works out handier/easier for me. - 'Doc [/QUOTE]

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