I've got a basic 100W transceiver with a USB soundcard built in. When I try to use a digital mode above 10W or so, the USB hiccups and my software (FLDIGI, WSJT, etc) crashes, and usually, the radio is left in xmit. :-(
I'm getting to my wits end trying to deal with this.
Setup:
* IC7300 connected by USB to desktop computer
* feeding separate 20m and 40m dipoles through RG8/U and MFJ949-E
* Antennas are mounted in a tree in a vee, the 40m is about 30 feet up, the 20m is about 25 feet up. Because of space limitations the conductors are not 180 degrees opposite from each other in azimuth. It's more like 150 degrees.
* Antenna feedpoint is almost directly over the shack
Things I have tried:
* replaced my old antenna (G5RV hacked various ways) to these bog-simple dipoles
* small fortune in mix-31 ferrites. Have them on the AC cable to the rig and computer PSUs. Have them on the DC between the rig PSU and rig. Have on the USB at the rig end and at the computer end. Have an MFJ915 choke on the feedline.
* taking tuner out of the eqn (SWRs are fine anyway, and there is an internal tuner in my rig that can handle them fine. I got the tuner to deal with my old antenna)
* I don't have a great grounding setup. I have tried floating everything, and I have tried grounding everything together to regular electric service ground (which is only about ~10 feet of solid #12 and a few more feet of solid #6 to the ground rod)
So far, no luck. Still the same problem. Radio keys up, maybe a second or two of modulation, then USB and fldigi die and radio is left in xmit (but with no modulation).
I *think* this may be a classic "RF in the shack" situation, but I am not entirely sure it's because of feedline currents. It could be from that fact that the intentionally radiating part of the antenna is so close. How do can I find out the source?
I'm thinking of pounding a new ground rod just for the station, along with that expensive ribbon braided grounding conductor to reach it. I have no confidence it will make a difference, and it is more money and effort just to find out. I would think that in a dipole grounding shouldn't be such a concern, anyway.
I can use the radio at full power with a key or the hand mic. The radio seems perfectly happy. Furthermore, the computer itself doesn't crash. I'm assuming it's the USB connection. I guess it could even be the USB chip in the radio.
Sorry for the long post.