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I also have a SSTRAN unit. Currently, my antenna is about 7ft of wire, stuck to the wall with push-pins. Not the best, but I can actually receive a good signal over 100ft away, using the radio in the truck. One of these days I’m going to buy another SSTRAN to use with an outside antenna.
As for hum, I had a problem with that, also. In my case, I had three culprits. The first was a UPS in my computer room. In reality, it wasn’t the UPS, it was the power cord. I changed the power cord and the hum disappeared. The old cord was thinner, so I suspect that either it didn’t have a ground wire, or the wire gauge was just too small. This was inducing hum into the transmitter, as the SSTRAN is situated about 5ft above the UPS.
The second case was with the old tube radio in the living room. This had a noticeable hum. Again, it was caused by a UPS. The radio wasn’t plugged into this UPS, but my TiVo was. I tried switching power cords on the UPS, but no luck. I finally switched the UPS with another brand to silence the hum.
The third case wasn’t a UPS, but a surge strip. After repairing another old tube radio to use in the computer room, I found it had a bad hum. I had just put all new caps in the radio, so I suspected it wasn’t the radio. When I plugged the radio directly into the wall outlet, instead of the surge strip, the hum stopped. I was surprised about this, as the surge strip was a Tripp-Lite (although an old one).
What this proves is that you need to suspect almost anything as being the source of your hum. As for the SSTRAN, I have never had a hum problem directly related to it.
You may also want to get one of those cheap AC line testers (Radio Shack, Home Depot, etc.) to make sure the outlets in your house are wired correctly. Even if the house is fairly new, it wouldn’t hurt to check. Besides, those testers are cheap enough.
One other thing to look at is the orientation of your antenna. If it is close to an AC line that is in the wall and especially if the antenna runs parallel to it, that will induce hum into the transmitter. I originally had that problem and moved the SSTRAN across the room.
As for ground loops, simply unplug the audio cable from the SSTRAN to see if the hum goes away. If that is the problem, Radio Shack used to carry isolation transformers. Jameco and other hobby electronics places also carry them. You’d need to solder on a jack and plug to use it as a pass-through for the PC sound card output.