Long time lurker, first time poster here. I recently built a 60m-15m QMX and I am having some trouble getting good reception on 15m and 17m (see attached RF sweeps). I should mention that I am using a Rev 1 board purchased in 2023, but with a mid-band component kit from 2024. Here’s where I’m at:
I get good power (4-5w at 12V) out on all bands, and my LPF sweeps look like the firmware manual
60m-20m RF sweeps look more or less like what’s shown in the manual. I use a QRP Labs 50 ohm dummy load for the sweeps.
When I connect to an antenna, I can hear FT8 signals on 40m and 20, but not on 17 or 15
Because the lower bands seem to receive OK, I suspect an issue with L401a, C401 or C403. However, 20m uses L401a and C401 and is OK, but 17 also uses those and is not good.
I reflowed solder on all 3 taps for L401a and the capacitors, with no change. I’m pretty confident I’ve burned off all the enamel at the junctions at this point. I get continuity at all the points shown in the Rev 1 manual (plus at pin 6 of IC402, which I think makes sense because I’m using all 4 connections for L401 instead of just the 3 with the low band version)
I did a factory reset, with no change
I’ve counted the number of turns on 401a more times than I’d care to admit, and keep coming up with the same number I’m supposed to have (24 turns, tapped at 15)
I confirmed that C401 and C403 are the correct values printed on the component, and don’t appear to have any physical damage
?
Trying to figure out my next steps, but coming up a bit short. All I can think of is to replace capacitors, and possibly re-wind L401a. Or, even less ideally, replace IC402. I don’t have an oscilloscope (or any real expertise to use one), so my ability to diagnose is somewhat limited. Before I start swapping out components, is there anything else I should try looking at? It’s been fun building this kit and I have managed to iron out quite a few kinks along the way by reading posts on this forum. However, this one has me stumped.
