How not to build a QMX... | HamRadio

In this epic (=boring and long) video I give my experience with building the High-Band QMX transceiver from QRP Labs and plenty of bad advice.
The first part of the video describes some of the problems I had. In the second part we look at the diagnostics menu and what my QMX shows there. I think it is mostly OK and functional.
I did one successful (but tough) POTA activation with it, however I also saw some weird behavior and of course that makes you wonder...
Make sure to also watch the QRP Labs video "52 tips for building your QMX successfully".
This video contains a treasure trove of information that helps avoiding common mistakes!
Timestamps:
00:00 Intro
00:11 Deboxing Timelapse
00:55 Tilted power connector
03:15 Fixed inductor and diode orientation
05:24 Squeezing toroid windings
07:23 RWTST transformer and SWR bridge
09:18 Trifiliar coil
09:50 Burning off of enamel on the THIN wire
11:08 General impression and advice
12:01 Tips on building the control board
16:24 Building the LCD board
21:08 Diode mod. on Q508
23:10 USB port problems / Usage
25:00 QMX Terminal menu
25:43 Random observed failure with RX filter sweep
26:46 Audio filter sweeps
28:17 RF filter sweeps
30:20 Image sweeps
31:19 SWR sweeps
32:18 TX output power on all bands
34:07 Outro
Music:
URL: remix.kwed.org/remix/6951
Title: Myth
Arranger: Eivind Sommersten
Composer: Jeroen Tel
#hamradio #amateurradio #qmx

[@AndreasSpiess]

I also vote for leaded solder. Much better for such builds! I turn 67 and am still alive. So leaded solder seems not too dangerous 😉

[@jakebrodskype]

The most educational videos include where people made and recovered from mistakes. I'm about to start my QMX build. Thanks for the experience.

[@redtide08]

I just ordered a kit and this is an EXTREMELY helpful primer, especially regarding care orientation of parts to not physically interfere with each other

[@labcat73]

Thanks for your kind comment!
Don’t forget to watch the QRP Labs video "52 tips for building your QMX successfully".
This video here was just my build experience and the problems I had. Hans video has many more tips and tricks in them than mine.
73

[@qrplife]

I’m in the middle of building a hi-band QMX right now. Thanks for sharing your results.

[@labcat73]

Hope the build goes well!

[@Kinetic79]

My 20m bandpass looks like yours. All in all, close to the same across the board... your 10m is a little better than mine. My SWRs are also similar... and considering I built for 9V--the wattage out pattern more or less follows yours.

[@harihurtig6157]

I'd very recommend an enamel stripper (Bernsten 5-181 or similar tool from Knipex etc).

[@barrymayson2492]

I got a set a couple years ago as a guy recommended them on UA-cam. They are the best way to strip enamel copper wire. I don't think they were that expensive.

[@harihurtig6157]

@@barrymayson2492 I got mine for 8 EUR and did finish multiple kits without any contact problems. I guess this is one of the tools where you only know what you had missed until you've tried it.

[@nevellgreenough404]

Thanks for the tips! I recently completed a high-band QMX successfully. I'll try your suggestions about bunching several toroid windings for improved output. I had considerable trouble with soldering the 8-pin connector on the rotary encoder board. Seems like the plating on the pins was corroded.
By the way, one comment on powering the unit. I had the "brilliant" idea to put two 5V power banks in series for slightly less than 10V on a 9V-wired unit. Don't do this. The unit works fine on 10V, but a noisey USB-A connector caused rapid 5V-10V input voltage fluctuations. This threw the software-controlled regulating loop on the internal 5V Vcc into convulsions that damaged something on its power board. It still barely regulated but with a completely wrong duty cycle. Luckily they offer replacement power boards in the shop! All is well again.
Once again, thanks for the tips. 73s and see you down the log..... N2GX

[@labcat73]

I think you are right: I had similar problems, but thought it was me cutting the pins short before soldering. Not sure if there was something wrong with the plating of the pins or if the long pins of the connector and/or the small spacer PCB were just an excellent heat transport sucking the heat away. - I forgot to mention that.
Thanks for the heads up about powering the unit! I wanted to try 3 x 3.7V 18650 LiPo cells, but managed to buy some super fake scam cells in the first attempt on eBay. 😆
73

[@Kinetic79]

I followed Ryu*'s (sorry exact spelling isn't correct), and got a couple of 1500mah 9.9V nominal 3S LifePo4 transmitter pack batteries for like ten bucks each from HobbyKing. Could be an alternative for you, if you want fairly compact. You'll need a balance charger that handles "LiFe" batteries though--got one that handles LiPo, LiFe and NiMh on ebay for like $18, and these batteries have the compatible white-colored 4-pin balance charger plug.

[@patrickhall5739]

Congrats on the build!
I just finished a low band version. My audio and Image sweeps looked ok, very similar to yours, but my RF sweeps were way off on the db side of things. Around -50db. From what I gather on the forums, it's an issue with the L401 toroid. maybe an issue with the jumper. Just thought i'd share my results.
73!

[@labcat73]

Thank you!
I still have to start making more QSOs with this to see how sane it really is.
I am sure you will get your build sorted! The last 5% are always the toughest bit in any project. 🍀