so this has been driving me nuts for about two weeks now. my 7300 started throwing high SWR warnings on every band, like 3:1 or worse, but when i slap a dummy load on the antenna port it reads flat, 1:1 no problem. transmit power looks normal, receive seems fine too. the antenna system itself checks out — ran a VNA sweep on everything from the feedpoint and nothing changed out there.

at first i thought maybe the internal SWR bridge went wonky but im not sure how to even start diagnosing that without schematics. does anyone know if theres a known failure point in the SWR sensing circuit on these radios? ive seen mentions of a directional coupler section somewhere in the RF board but i cant find anything specific. the radio is about 4 years old, out of warranty obviously, and i dont really want to ship it to Icom unless i absolutely have to. happy to get in there with a scope if someone can point me in the right direction

had almost the exact same thing happen on my 7300 about a year ago. turned out to be a cold solder joint on the directional coupler section of the RF board — you can actually find the service manual floating around online if you search hard enough, and the coupler is on the main RF unit somewhere around the antenna relay. what i did was just reflow the joints around that whole area and it came back to life. not saying thats definitely your problem but its a pretty common failure mode on these, especially if the radio runs warm a lot or youve been doing any digital modes at higher power levels for extended periods.

also worth checking the antenna relay itself — the 7300 has a relay that switches between the main and sub antenna ports and i've heard of those getting intermittent. you can usually hear it click when you key up. if its clicking but the SWR is still weird, probably not the relay, but if its intermittent or sounds different than usual thats another thing to look at.

the dummy load test basically confirms the RF path from the PA to the SO-239 is okay which does narrow it down to either the sensing circuit or something up the line. what does the ALC look like when you transmit into the antenna? if the ALC is going nuts but the power output is normal that would tell you something. also curious what the SWR reads on say 40m vs 2m — oh wait 7300 is HF only never mind. anyway i'd grab the service manual before doing anything else, icom service manuals are actually pretty good about showing the bridge circuitry and you should be able to trace the forward and reflected voltage sense lines with a meter without too much hassle