On Mon, Apr 21, 2025 at 11:45 AM, Jan Szumiec wrote:
The L401 transformer has some looseness on one of the windings (1mm) - would that matter?
No, that won't hurt anything, and does not affect transmit (T401 is only used on receive).
Also, it appears that the SWR is a function of power. It is greater when I measure it at 10/20% and lower when it is 50%. Is this normal?
No, SWR is not a function of power, if everything is operating correctly.? The SMA terminator from your nanovna kit should work fine at the lower powers, but is not built for 5W - so don't use it with full power, or you may burn it out.
?
The SWR and power displayed by the QMX are both read from the bridge circuit, of which T507 is the principle part.? What the CPU actually reads from that bridge is the peak forward and reverse voltage (divided by 10), from which it calculates power and swr.? So if one of the solder joints to T507 is a bit 'flaky' or 'cold', it could cause either the forward or reverse voltage to be incorrect or 'noisy', causing incorrect measurements.? So check those and re-flow them, leaving the iron on the connection for several seconds in case there is still some enamel that needs burned away from the wires.? [There are also SMD resistors, 2 diodes and 2 capacitors in that bridge circuit - it is less likely, but if one of those have been disturbed, it could also cause this issue.]
