QRP-LABS QMX *PLUS* PART-1

Last Easter I built a 5-band QMX and although I found it quite a challenge, it worked from the get-go and I was really pleased with myself! I get a lot of pleasure from building electronic kits and this will be the sixth one from QRP-Labs. 

My only gripe about the QMX build was that the design left the components incredibly tightly crammed in, and I wondered why they hadn't made the PCB just 10mm wider. But since then, I have read Hans Summers' document explaining that, for him, it was a design-challenge to come up with such a compact design. Well, he did an amazing job!!

Anyway, here we are a year later and I see that Hans has released the QMX+ transceiver kit. This time, the design has much more space between components and I'm anticipating that the build will be far easier than the original design.

So what is a QMX+?? Well it's a high quality 12-band MultiMode (CW/DIGI) Transceiver which can be purchased as a self-build kit or as a pre-assembled unit - it's worth noting however that there is a very long waiting list for pre-assembled units - maybe up to 6 months 😮

In terms of functionality, the "PLUS" version is little different to the standard QMX but it has the advantages of being able to house a GPS unit, an SWR Bridge, a Real Time Clock (battery backed), a Developer's Kit and maybe even an ATU in the future. Hans also has other "secret" plans for the ongoing development of the QMX+ including SSB Mode which will be awesome!

I feel (and I may be completely wrong) that the QMX+ is a big step toward the release of the fabled QSX which will be an All Mode transceiver with who knows what features. 

I currently own a couple of (tr)uSDX transceivers and these are simply amazing little radios which are multi-band, all-mode SDRs with built-in sound card, speaker, mic, keyer, PTT, etc. But their performance is far from perfect. Don't get me wrong - I love them - and when you're up on a hillside playing POTA or SOTA, their performance will bag you many contacts for little outlay. But they're just not in the same league as a QRP-Labs product.

I'll always remember when I built my first QRP-Labs kit - the QDX. It went together well and it performed superbly!! I was getting better results on my 5W QDX than my Multi-Watt IC-7300.  I was (and continue to be) very impressed!

Sorry - I'm rambling. Let's look at the QMX+ Kit. It arrived in a single box which contained all the relevant components, each type being bagged separately.  I'd also ordered the optional GPS Module plus (of course) the metal enclosure. 

The quality of this kit is extremely high and I've yet to come across a QRP-Labs kit with missing pieces. The aluminium case is strong and well finished, with sharp text on the end plates.

The Assembly Manual for the QMX+ is extremely good (as usual) and I intend to follow the instructions to the letter, just as I've done before. 

In addition to having access to the manual electronically, I also decided to print a copy so that I could read through it prior to starting the build and highlight bits which I think warrant special attention, making notes in the margins of the page. I also use the printed manual to mark off each completed section.

I had decided to do this build at the weekend while I was at our caravan - nice and peaceful with no distractions. Prior to going there though, I wound all the toroids and then bagged them individually in tiny sealer-bags with ID labels.

All pretty straightforward but
the most tedious was L506

Before starting the build, I laid out all the components and marked off the capacitor values. Once that was done, I fitted the caps, the diodes and the inductors. Very simple.

After that I installed the BS-170 transistors, clamping them in place before soldering. 

Next up was to install all the toroids and the trifilar. Since I'd pre-wound these, it was a breeze to fit them all and once I've adjusted them as part of the 'tuning' procedure at the end, I'll probably drop a few blobs of hot-glue on them to keep them secure when the radio's in transit.

At this point of the build I realised that I was rocketing ahead and was being a little blasé, so I purposely slowed down and checked everything I'd done so far. 

I have to say that for whatever reason, I seemed to be struggling with my soldering on parts of the board. At first, I thought it might be my soldering station, so I switched to another soldering iron and things improved - this board demands a soldering iron capable of holding its own!  Of particular note, some of the solder-pads are TINY and it can be real difficult to get the tip of your soldering iron onto both the pad and the component at the same time. If you look at the adjacent image, you will see that some solder-pads are way, way smaller than others and some of the pads are barely visible.

When it comes to winding the T501 Transformer, you have to decide whether you want a 9V radio or a 12V. I opted for 12 and for this you are strongly advised to choose the "RWTST" method of winding (Really Weird Twisted Sister Transformer) and boy, it certainly is weird!

I'll be honest and admit that the first time I wound T501, I wasn't confident I got it right, so I unravelled it and started again. I was struggling to understand the diagram (see below).

Diagram From The Manual

In the hope that it will help others, I have redrawn this and although it makes sense to me, it may not to you 😂....

After that, I put the two power boards together and fitted them to the main pcb. You have to be very careful to read the instructions and slow down when you're fitting these. Read a couple of pages ahead before beginning!!

 

I then started fitting all the 'hardware' such as the BNC connector, power connector and 3.5mm sockets before installing the LCD panel and battery board.

With everything installed (don't forget the link under the GPS Board (if you bought one)), it was time to slide the PCB into the lower half of the enclosure. 

Before you do though, spend some time examining the pcb to see if any of the component legs need trimming down, because there's very little space between the underside of the pcb and the metal enclosure and it's very easy to end up with a short. 

I purchased some amazing little side-cutters from the local £shop which were perfect for the job! To be honest, I thought they might be junk, but they turned out to be the toughest fine cutters I've ever bought, so I went back and got another pair 😊

With everything put together it was time to apply power and see if any smoke emanated from the case 😬. In case I'd made a mistake (or two), I opted to use a current-limited psu to avoid damage on power-up.

 FIRST TEST >>>

When I switched it on, there were no lights, no display, no noise, nothing! And thankfully there was no smoke!

Before anything will work, you have to connect the radio to a computer with a USB lead and install the firmware, but when I did this, the USB was not recognised. I tried a different lead and even a different computer - nothing! 😰 

I checked and double-checked the pcb for any obvious signs of faults such as dry joints, solder shorts, etc, but there was nothing obvious. I could see 9V at the power switch.

I sought help on the Groups.IO forum and got nowhere initially, so I submitted a trouble-ticket at QRP-Labs but six days later there was no response from that either.

It's extremely disappointing when stuff like this happens and I know there's bigger problems in the world, but neverthless I'm feeling quite disappointed considering that I've successfully built 5 other kits from Hans (including the regular QMX) and a few from other kit manufacturers.

A few days on and members of Groups.IO started to make suggestions and I learned that there should be voltage at Vcc and Vdd but there was none on mine. The thread got busier and someone suggested that I try swapping out the Power Boards from my QMX to my QMX+.  Before I risked that, I decided to order a variable voltage/current psu to further reduce the risk of damaging the boards. With it, I could reduce voltage to maybe 7.5V and 200mA.

Before swapping out the boards, I recalled my soldering struggles and decided to reflow virtually all the connections to make sure that I'd not got a bad joint somewhere which was causing these issues. The Ground Plane on this pcb really does suck the life out of your soldering iron! 

I decided to remove the power boards and the GPS module. It was then that I discovered I actually had a short on Vdd. No amount of probing with my DMM helped discover the source of the short, so I’ve given up for now.

I’ve approached an electronics professional friend to see if he can afford the time to do some fault-finding for me. If not, I might have to order another and start all over again 😪.

Part-2 to follow!

73, Tom, M7MCQ.