Re: QCX-20 ... low output power (~1.5 W) #qcx #20m

Rob French (KC4UPR)

One more update.  Hopefully this will help narrow things down.

This occurs about 10% of the time, where when I go key down, I get ~300 mW output power.  

An additional thing I noticed...

When I measure (using the built-in RF power meter) the level at the drains of the final amp transistors, I always get a solid "5.2" on the display.  However, when I measure it at the output BNC center pin, it varies between 3.8-4.5... or else 0.32 or so.  So even when I am getting "good" output power, it's still not the same as what I'm seeing at the output of the finals.  More to the point, when I measure it at the transistors, the reading is very steady... constant 5.2.  When I measure it at the LPF output, it wanders a little.  

So I suspect this all indicates more and more that it's a problem in the continuity of the LPF, although I'm still surprised that I never see it change while key down (except for the slight wandering during the high power out).  What is the chance that this could be a problem with the LPF capacitors, and/or the coupling capacitor (C29 I think)?  Should I just go replace these all as a matter of course?

Also, for the coils, should I just remove, rewind, and reinstall, possibly with manually removing the enamel?  I attempted to use the "burn of the enamel" technique... maybe that just didn't work for me. 


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