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QMX - Looking for troubleshooting advice

 

My problem is low power on transmit, only on 20 meters.?

I bought the kit in Dayton, built it right away and had good output on all but 20 meters. I set the kit aside and today, I applied all of the updates...I re-wound L401 and swapped the two caps in LPF2. I updated the firmware. Here's what I'm measuring..

80M - 5.8 watts
60M - 7.0 watts
40M - 4.0 watts
30M - 5.6 watts
20M - 1.6 watts

I've stared at the schematic to see what component could be specific to 20 meters that I may not have soldered in well enough and I thought the LPF for 20 was shared with 30, so I'm not sure why I could get full power on 30 meters on not 20.?

I did the obvious things, checked for solder bridges and such. Any ideas on what I should check next?

73, Conrad, N2YCH
 

I would check the receiver BPF sweep under the hardware diagnostics menu. While it is about the receiver, it measures through the transmit LPF so there may be some clue in that plot.
 

Squeeze the turns of L513 together as close as you can

-Mike/w1mt
 

I fixed a QMX once that had a similar problem. ?I was stumped for a while. ?Then I removed L509 and replaced it with a new one. ?That fixed it for me. ?I think these inductors are pretty sensitive to too much heat when soldering them. The one I removed was more like a resistor and less like an inductor. ?Good luck. Jeff, W1NC?
 

I noticed that L509 is a 47uH inductor. Depending on the particular inductor model, the winding capacitance is usually on the order of a few picofarads, and the self resonance frequency can be as low as single digit MHz range. Above the self resonance frequency, the "inductor" appears as if it were a capacitor to the circuit. That may cause the LPF cutoff frequency to move lower. I think 47uH on 20m is probably ok in the majority of cases but I can imagine individual variability may bring it to an iffy zone in some cases. A smaller inductance may avoid this altogether. (Good to keep 47uH for the lower bands though.)
 

I don't see that as an option the QMX...it only has a GPS viewer option under Hardware tests.?
 

This didn't work, unfortunately. I took my 2.5 Watts down to 1.0 watt. Spreading them apart again restored the power
 

I found an equivalent part from a parts radio I have and dropped it in. Unfortrunately, no change.?
 

Thanks for all the tips. I spent a good part of the day today just inspecting my work, trying to make sure I had to cold solder joints again...I managed to get another 0.5 watts out so now it's up to 2.5 Watts. I'm truly at a loss.?
 

I'm not sure if that was the case with earlier firmware but mine does have that option in QMX.

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