[Elecraft] Horrible APRS QRM on 2 Meters

[Richard Beerman]

Wonder if anyone else has encountered this on 2 Meters? I am using a 12 ele K1FO yagi - about q12 dB gain on 2. That enters the shack where it is connected to a Downeast Microwave 50 Watt transverter with about 17 dB gain on receive. The output of the transverter is connected to transverter input on my old K-3. For the longest time, I was receiving loud QRM from what I initially thought were power line noise bursts. But, I became suspicious because these bursts were about a second or so in duration consistently. During this time, I was testing my setup for meteor scatter using the MSK 144 software found in the current WSJT-X suite. These loud bursts created huge red images on the monitor watching in 144.150 MHz, the MSK144 calling frequency.

I got suspicious that these signals were not simple electrical pole shorting noise. So, I connected a whip to my old TS-790S rig and tuned it to 144.390 MHz, the North American APRS frequency.  WALAAAAA, the signals on my monitor connected to a K-3 tuned to 144.150 MHz corresponded perfectly to the WPRS signals on 144.390 MHz, some 240 kHz away! The preamp on the K-3 was off. There were no other receiving preamps in line at the time. Later, I turned on an external 2 Meter preamp and all that happened was that the APRS signals were larger at 144.150 MHz. 

It appears that the front end of my K-3 simply folds up in the presence of strong signals that are WAY off the receiving frequency. I can tell you that connecting the same antenna/transverter to a Kenwood TS 590SG, there were no traces of the APRS signals. And connecting the TS-790S to the K1FO likewise produced no APRS QRM at 144.150. To me, with the presence of a number of strong APRS signals on 144.390 makes this K-3 extremely unusable on 2 Meters. I was running the K-3 noise blanker to handle the rest of the noise here but likewise, I also had noise blankers running on the two Kenwood radios as well. 

Any suggestions are welcome.  Dick  W5AK