Re: Successful assembly of QCX mini 40

howard winwood G4GPF

Hi Johan, my 40m QCX mini build went exactly as yours did, bezel tab and electrolytic, locking tab on vol pot.
My power started at about 3W, spreading the turns out raised it to 5.2W at 12v same as yours.
I follow your sentiments to Hans also for a great piece of work.
Just goes to show, if you follow the manual and have good soldering skills, you will have success.

Howard G4GPF

On 16 Mar 2021, at 01:20, Johan Bodin <> wrote:


I just finished building my 40 meter QCX mini and I'm happy to report that it works very well!

Assembly went smooth thanks to the *excellent* manual. The only problems I faced was an LCD bezel tab that collided with an electrolytic capacitor on the main PCB (fixed by bending the tab slightly) and the locking tab on the volume potentiometer that was bigger than the hole in the PCB (I simply cut the tab).

The output power was initially 3.2W with L1, L2 and L3 all tightly wound with turn counts according to the manual. Spreading the turns of L1 and L3 evenly over the cores and keeping the turns of L2 tightly compressed increased the power 2.1dB to 5.2W at 12.0V supply voltage. The L4 winding is spread evenly around the core. The BS170 transistors in the PA were only slightly warm after 1 minute key-down into a 50 ohm dummy load so the efficiency is good.

I did a quick "manual MDS check" with earphones and a signal generator (HP8640B). I could hear the signal at -133dBm (0.05 uV) and at -127dBm (0.1 uV) it was strong enough for reasonably easy CW copy. Assuming that 50 uV into 50 ohms (-73dBm) is S9 and that each S step is 6dB, -127 dBm is equal to S0. In other words, the sensitivity is better than good enough.

Thanks for a great kit Hans!

73 de SM6LKM Johan

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