QRP-LABS QMX BUILD

EASTER BREAK : the perfect time to start a new radio kit? The QMX was not going to be straightforward - I knew that - but it was a challenge that I was willing to take on. I’d just completed the RADIO-KITS EXPLORER and felt ready to start another project while I was on a high 😂.

The QRP-Labs QMX doesn’t have a lot of parts, but it is a tough little cookie - much more so than the Explorer. It’s not just a case of soldering a few bits and switching on - there’s a lot of tiny toroid winding, including some “Weird Twisted Sister” transformer work and then there’s the very tightly spaced components which make soldering a PITA (especially considering the larger ground plane). 

The manual is pretty good, although it sometimes uses images which are similar to the QMX but not actually the QMX. At the end of the day, this kit is far from straightforward. There’s a lot to cram into a small space and it sometimes feels like an Airfix kit because of the modifications you have to make to standard components. 

But before moving on, let’s all bow to the greatness of Hans Summers and his amazing design ideas. WOW! How the heck he comes up with these layouts I have no idea! It’s all very, very clever. But then when I try to squeeze the toroids into the tiny spaces around other components, I find myself saying “Would it hurt to have the PCB an extra 10mm wider”??

If I had to come up with a single tip for builders of this kit, I would say pay attention to the spaces around the toroids when placing the caps and diodes. If I was to build this thing again, I would have sat them just a fraction higher off the pcb so that I could manipulate them slightly to make a bit of room around the toroids. That way, you can move the enamelled wire around to get the best performance. 

Apart from the fact that everything is squeezed in tightly, the kit was pretty straightforward to complete and there were no massive issues, so I won't bore you with step-by-step details, because the manual will provide all the help you need. Instead, I'll post photos of my build, showing views which I would have liked to have seen myself.

I have to admit that I am extremely pleased with myself for having successfully built this kit without a single error. I powered it up and after installing the FirmWare, it worked immediately, without a problem. I’d heard on the forums that many folk were experiencing problems and maybe it’s being aware of those problems that made me more cautious. Whatever it was, I feel quite proud of myself 😂

Here we go...

Damaged in transit
(But doesn't effect it)

These PCB Stands are a MUST!

Hans suggests topping up these holes to
improve structural integrity of the USB-C
connector, but they're WAY too small for me!

This photo shows the orientation of
the diodes for those who aren't sure

BS170's were actually soldered in with
the screw and washer in place.

Tiny, tiny toroids!

Needed a drink
after those toroids

This would have been soooo
much easier if different coloured
wire had been supplied

I broke off the terminal on one of these
and had to use a cut-off to repair it

All done!!!

IT'S ALIVE!!!

I'll post more when I get chance to use the QMX out in the field. Right now I don't have a resonant antenna with me and the swr is too high to operate on the one connected.

The good news is - it all seems to be functioning well on receive. More soon.

73, Tom, M7MCQ.

UPDATE (same day) - Just connected to a G5RV and used RBN to get a quick report on my CQ TEST M7MCQ transmissions…..