… But How? Time expended thus far, 2 weeks.
I’ve recently been playing a little bit on sideband on my IC-7300 and have been getting reports that i should check my station because it sounds like i’m getting RF feedback into my radio. I’ve been using the radio primarily as a data radio and participate in a nation-wide net. I have licensed the VARA-HF modem and have an SCS P4-Dragon 7800 Pactor modem.
I normally don’t do much on sideband but i do sometimes pick up the mic. Last week was the first time in a while. i got bad more bad reports, so i asked a local friend to do some testing with me and he hears the noise too. It is not as pronounced when I reduce power… my first clue.
To test on my own, i dusted off another radio and found a free frequency and transmitted at 100 watts and 5 watts and confirmed the issue. I then started disassembling stuff to isolate the problem. I took the deep cell batteries out, disconnected the charger uncoiled coax… everything i could think of. I even changed antennas to no avail.
Then it occurred to me to start removing cables from the radio itself. I removed everything except the antenna coax, the mic and the power and performed the test. No RF interference. I got John to confirm. Then, one-by-one, i started hooking the cables back up to the radio. The speaker, tuner, and USB interface to the computer were not the issue, the interface to the SCS pactor modem is.
The pactor modem is a fairly new addition to the station and it works decent. Little did i know that the interface cable was allowing RF feedback into my radio. I added it to the station back in the spring. Apparently running 5 or 10 watts for data comms weren’t affected by it much. I was able to send and receive data and participate on the net. When i increase power and talk sideband, that’s when the issue crops up. So now it’s time to investigate thee interface cable, it’s a premade cable that i purchased when i got the modem, i’m likely going to need to build a shielded cable.