QCX - 30M Transceiver - Mods

Two more mods for my 30M QCX.

I have already completed several mods, as detailed in QCX - 30M Transceiver .  The final one I did last year was intended to increase the power output, but was only marginally successful.

Recently, I purchased a 20M QCX, but after finishing construction, I found that the ATmega328P microprocessor was not working.  Hans, at QRPLabs, had seen this problem before and was happy to send a replacement - and I ordered an additional latest firmware chip for this 30M rig.  While waiting on the replacements to arrive, I elected to replace the capacitors in the low-pass output filter.

I replaced C25 and C26 with 560pF silver micas and replaced C27 and C28 with 270pF silver micas.

These capacitors were huge compared to the originals - so I had to get creative in placing them.









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Note that C27 and C28 had to move to the bottom of the PCB - and were tilted slightly to provide clearance for the enclosure.




I am fortunate to have a low-priced but effective solder-sucker that I bought some years ago.  This would have much, much more difficult without it.

Here are the parts I removed.  The largest is about the size of the head of a kitchen match.  I used silver micas as I had the correct values for the 30M QCX on hand.





Just as I was completing this modification, the replacement microcontrollers from QRPLabs arrived - with firmware version 1.00f.

The only volatile information that I wanted to keep was the correction for the 27MHz frequency reference (Entry 8.5:  27.004.550), so I made a note of that and replaced the 1.00b firmware with 1.00f.  As expected, no re-alignment was really needed, but I touched it up anyway.

After all these changes, I now have 3.4W out measured with the same equipment as earlier.  This is just about what the designer predicts, given my 12.4V motorcycle battery power supply and the polarity protection diode.

I am pleased and will call this good for now.

My thanks to W5IQS for suggesting mounting the capacitors on the bottom of the PCB.   And to Hans, of course.  The more I use this little rig, the more I like it.

Here is an image of the 30M QCX in its new enclosure.


cln - Nick
WB5BKL