What did I do wrong?
I built my 50W PA for 20M - This is my third QRPLabs kit, having successfully built two QMX first time 'round (high and low band versions) so I get the idea of how the manuals and instructions tend to be set up, and I think I got the PA completely right, except that the input SWR is a mess, hovering around 3.0 at 14 Mhz. This of course isn't going to work.? I don't want to smoke my QMX. I'm crazy about these little radios. They both work so brilliantly.?
(Note, I was manually keying the PA to test before the latest 1_00_016 firmware came out, thanks for that, PA key-up is working as expected with the new FW)
R5 is adjusted as per the manual, plus tried a few percentage points +/- either way - no improvement. My antenna is a meticulously trimmed-for-20 dipole with excellent performance. I've also tried a range of different voltages from 12-20, and there's no meaningful difference in the SWR sweep when I change that variable. Also, the nano-VNA more or less agrees with the SWR sweep that shows high SWR on 20M. And of course, I'm doing these sweeps with the power amp keyed.?
I'm not an expert in PA, or really analog anything design, so I'm at a loss here. Nothing really sticks out on the schematic at this point in my education.? I re-wound the trifilar T1 a second time just for fun with a brand new set of wires, but the outcome is identical. High input SWR.? What if I removed a turn from the T1 transformer? Would that shift this nice low SWR dip I see at 10 mhz? Or added MORE turns?
?
If I wanted to run at 30M, then of course it looks like I'd be in excellent shape here, but I need 20.? As I understand it, having a SWR of 2 into a PA isn't even unusual, but 3 is a whole other story.?
I would appreciate if the group could share their knowledge and help me better understand what's going on and suggest avenues I could pursue to correct this. And please be kind, remember I'm new to this and trying to get into the hobby.?
Thanks!
Andy KA1PLU
