QDX 4-band 5W Digital Transceiver

I finally received the QDX kit that I ordered back in July. This is the first kit that I’ve purchased from QRP Labs. First impressions were good. The kit was packaged well and seemed to be good quality. The transceiver itself was a lot smaller than I expected.


The board that I received was revision 3a. When reviewing the excellent documentation and build guide, I found that this board revision contained a short, which is disappointing. According to the manual, you need to cut into the board to sever a connection between a via and a ground pad.


Once this was done, I began soldering in the capacitors.


Next, diodes.


A few inductors.


Next, I installed BS170 output transistors. I added some thermal grease and then tightened down the washer and nut that serves as part of the heat sinking for the transistors.


Now, onto my least favorite part of building radios, winding toroids. There are different turn ratios for the binocular core depending on the voltage you are using to power the QDX. I opted for 12 volts, so I wound it 3:2.



I added on the antenna connector, power jack, and the rest and then installed the board in the optional enclosure.





This was a mistake. I should have tested everything first. The QDX itself was working. I powered it on and it was recognized by my laptop and wsjt-x. I played around with FT8 for a bit, but got no responses. I checked the output on my new spectrum analyzer and was getting really low power out. I took it back out of the case and checked the output signal on the scope and had a really distorted waveform.

I ended up replacing all four BS170s with others I had on hand and tried again and this time, things worked as they should. I’m not sure if the BS170s that came with the kit were bad or I screwed something up. Maybe one or more of them blew up on first TX. I’m not sure, but I now have a working unit.


I put it in WSPR mode for about 30 minutes and was getting picked up in Europe and Australia.


I’m quite happy with the little unit. I haven’t worked any FT8 or other digital modes yet, but I’ll be trying those out soon.