How not to build a QMX... | HamRadio

[@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

[@ai5dd]

Great info! Watched to the end. I will be building the mid band (60-15) QMX starting this weekend! 73 de AI5DD Joe

[@labcat73]

Thank you Joe and good luck with the build! Slow and steady does the trick. Also watch Hans video "52 tips for building your QMX successfully". It contains a plethora of good tips!

[@ai5dd]

@@labcat73 my build turned out better than expected, only had to adjust the two band pass filters for 17 and 15 meters. 73

[@labcat73]

Great news! Have fun operating with it...

[@blugoose86]

Not telling anyone how to repair a mistake, I found that using low melt solder is easier to remove a component from the PCB and then wicking up the excess solder gains a higher probability of NOT damaging the PCB or the traces. You just have to make sure that once the part has been removed, you wick up all the low melt solder from the board AND the component, as low melt solder is very brittle.

[@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!

[@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.

[@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.

[@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. 🍀

[@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 KZbin. 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.

[@GarySchiltz]

I'm a total noob at building, and have no soldering tools, nor test equipment other than a multimeter. Given that, would some good advice for me, be to get some simple starter tools and then take on a few much simpler projects? Any recommendations on projects that I wouldn't get very upset if I totally messed them up, but learned from them? Any suggestions for a very basic set of soldering tools? My "final" goal is to build a QMX and/or QMX+, even if it takes me a year to develop the skill. 73 de W5PAZ

[@labcat73]

Hi Gary! This is a pretty open question and maybe KZbin comments are not the best forum to answer this. I invite you to join the Discord channel of "The European Ham Radio Show" via www.hamshow.eu/discord . There are a lot of nice guys online all the time and you can ask in the DIY channel for recommendations for a beginner setup. I would suggest to get some decent basic tools and start with some easier kits. QMX is really something for a more advanced user that already has built several kits. The QMX+ is an easier build, as there is more space between components and things are not so tightly packed. So maybe as your 3rd or 4th kit you can tackle it. Start with some easy through hole component kits first. As a basic setup I would get a soldering iron that uses the JBC T12 cartridges. On eBay, AliExpress or Amazon look for 'KSGER T12' . Then a holder for the iron, some solder wick, flux, leader solder if possible, some good quality side cutters, a good tweezer and small pliers for bending wires and a basic set of small screwdrivers. If you want a mechanical solder sucker get an original Soldarpullt. Everything else I tried did not work. An antistatic mat can be added at a later point. Something to hold your PCB like a "third hand" and depending on your eyesight maybe one of these desk lamps with a built-in magnifying glass is also a good idea. Especially with the tweezer, side cutter and pliers don't buy the cheapest stuff! Decent tools make kit building fun and bad tools can make things sooo much harder. I have seen tweezers made out of cheese. Yes they are cheap, but can go straight into the bin after purchase 😉. I hope this helps a little.

[@GarySchiltz]

@@labcat73 That is extremely helpful, thanks!!!