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QRP-Labs QMX

This page is work in progress and may be updated frequently (last update : 2023-08-17 12:29UTC). 

Page content : 

• Introduction 
• The manual
• Let start building   
• Mindfull toroid winding
• Again mindfull toroid winding
• To Buck or not to Buck
• Control board
• LCD Display
• Smoke test
• Boxing it up
• My tips

Introduction

Loving the kits from QRP-Labs, and when Hans Summer announced his new QMX multi-band multi-mode transceiver I knew I wanted to buy and build one. And when he added it to his webshop I didn't hesitated for a moment.

Hans learned from the QDX that even a large stock, could be sold out in a few days, so he ordered multiple large batches and reading the note on the order page, it's was a good move. Due to the high demand and the Dayton Hamfest where Hans attended (and he also gave a presentation there see FDIM May 2023 seminar slides), it took a few months for my kit to arrive, but today (24 july 2023), the mailman didn't have to ring twice). A package from Turkey was handed over to me containing :

• QMX multi-band multi-mode transceiver
• http://shop.qrp-labs.com/qmxcase  

And that evening I took some time to take a close look.

 

The manual

As with every kit which Hans sells, the also was a very nice manual for the QMX multi-band multi-mode transceiver (link).  Chapter 1 contain a Introduction  Chapter 2 contains a list building general guidelines, images of the PCB layouts (track and component placement),  technical specification and the full Parts list of all components in the kit and photo's of a finished QDX allowing to kit builder get a idea about what to expect. And after sub chapter 2.3 Inventory parts helping the starting kit builder to identify parts, the fun starts.

Let start building 

As show above, the QMX PCB isn't cut in the factory for individual sub PCB's, so you have to separate them your self. 

Some careful cutting and bending over the V-groves to free the boards. 

As Hans states in the manual, the rough edges must be filed flat carefully, taking care has to be taken not to damage any nearby SMD components. Especially one should watch out when working on the small power supply boards which have SMD components very near the edge. When all PCB's where freed and the rough edges where taken care of, it was time to wash hands and clean the table with a damp cloth (you don't want the PCB dust all over the place). 

One nice Easter egg on the QMX is that the QMX comes with QRP-Labs Keyfob to show you like QRP-Labs kits. IMHO I see possibilities for new items in the QRP Labs fashion boutique.

Next to the great wanna have stuff they already have in the QRP-Labs webshop (as shown on this 1 year old photo).

After the tea it was time to sort the capacitors. Because my eyes are getting worse, I used  a magnifier to sort the capacitors and write the value on the paper tape. 
That way I don't have to continuously use the magnifier to identity every component. 

Section 2.5 describes the placement of the capacitors so I started with the construction ( also placed the diodes and the inductors). 

At first I used the PCB holder and my Velleman Magnifying lamp (3 dioptre) for the soldering, 

 

but after inspection with 1985 Olympus 10x/20x microscope 

I found out that even though I thought I used a minimum of solder, the PCB design is so compact and the islands are so small, used way to much (know shorts luckily, but still, way to much).  

So I changed my work flow : first install components on the PCB in the PCB holder, then soldering underneath my microscope. 

And after a few sections it's starting to take shape.

Section 2.8 describes the placement and installation of the 4 BS170 FET's. I first put the BS170's in the holes, pressed them down and then bend them over as close as possible into shape. 

and after that I place the bold, washer and nut to keep them into place so I could solder them. 

 

For now I'm happy with the result and put it all in the box for this evening.

  

Mindfull toroid winding

Kind of . . . 

As of section 2.9 the fun really starts. I don't know why, but a lot of OM's hate winding toroids, coils etc. For me it's a very relaxing thing to work on.

As in the QDX manual Hans writes in his QMX manual : 

It is a good idea to de-burr the toroid because sharp edges can damage the insulating enamel on
the wire – however be careful since the ferrite is brittle and can easily be broken. So GENTLE
scraping of the edges with something sharp like a knife is possible.

Just like I did on the QDX, I took a closer look at the BN43-202 binocular ferrite and indeed there were a few sharp edges. To remove them I use my old scraping tool which I own for decades. 

 I used have to place the tip of the tool into the BN43-202 binocular ferrite and turn it a few times and all the sharp edges where gone. 

And following the instructions in Section 2.8 I wound the BN43-202 binocular ferrit.

 I remove the enamel off the wire I use a X-tal knife and a stainless steel plate (see also this how-to).

By just turning the BN43-202 binocular ferrite 4 times, all enemal is scraped off and 

The result. 

 I always cut some the wires on different length, which allows the insertion process to be more easy. 

Soldering the big boy into place. 

Then I wound the tapped inductor L401 according to section 2.10. Basically there isn't any thing special about it when you follow the manual, but don't do what I did. Even after reading the manual, I blindly put 19 turn tap in the X hole. 

It's a good thing that Hans indicates that between 3, 4, 5 and 9 there should be a connection and 6 should be isolated. So in my case 5 didn't have a connection to the rest and 6 did and I had to do some de-soldering. Which is do-able, but because of the dense component population and lots of very small SMD parts at the bottom, you need above average de-soldering skill and tools to fix that.

L502 was so straight forward (10 turn 0.6mm / AWG #22 wire wound on an FT37-43 as described in section 2.11) that I even forgot to take a picture.

The same goes for all the Low Pass Filter toroids. Just follow the table as described in section 2.12. I wound all the toroids before installing each allowing me to position them a little better because the space for these toroids is limited and it's a tight fit. 

Close up of the low pass filter toroids. I told you it was a tight fit. 

 

But it's enough for now. The other toroids and parts have to wait for a next free evening. 

Again mindfull toroid winding

There is one toroid and transformer left. The last toroid is  trifilar toroid T401 as mentioned in section 2.13. 

But first we have to twist 3 wires to a trifiar wire. For that and normal bifiar wire, I use the technic as shown on this page. 

 With the fresh twisted trifilar wire, we follow the winding instruction of the QMX manual. 10 turns through the T30-43 toroid.

Once the turns are in place, we unwind the legs of the trifilar wire and I like to use self clamping tweezers to hold the toroid. Preventing it from jumping around on the workbench.    

 I scrape of some of the enamel and identified the A, B and C wire. 

Once identified I cut the A, B and C wire to different lengths. Not only to identify the wire but also to allow insertion to be more easy (ever tried to insert 6 wires a the same time? I did and didn't like it). 

Next on the list is the transformer T507 and it is wound as described in section 2.14. Unfortunately I took to much wire for winding the previous toroids so I was 20cm short. 
I took 0.4mm wire from my own stock and used that. I don't expect it to be much of a problem (time will tell though). 

This transformer wasn't going down easy and it took me at least 15 minutes to get it in the correct position because the 0.6mm wires are quite stiff and didn't cooperate.  

 Next on the list where all the connectors. Placement is easy, but remember that Hans wrote : 

It is very important to install these carefully aligned so that they are straight and at right-angles
with respect to the PCB. The connector body should not protrude beyond the edge of the PCB.
3.5mm stereo jack connectors X202, X401 and X201 will try to NOT sit at 90-degrees, they will try
to sit slightly twisted; it is important to apply necessary force to hold them in the correct 90-degree
orientation with respect to the board edge, during soldering.

Trust me on that one, I was a bit to eager and forgot about the above. It took me a few minutes to correct the connectors. 

The first of the headers are in place.

But again it's enough for this evening. 

 

To Buck or not to Buck

And Buck it is....

In the QRP-Labs groups.io group, there is a post by Jaques PA3EVZ about a potential short circuit in buck converter between  Q104 and Q105. Although I didn't metioned it in the initial version of this page, I did did took a look at the 5V buck converter and double checked it with a DVM. My buck converter didn't have the short, but it worth checking. 

Thanks to Kees K5BCQ for reminding me to include this info and also I want to point out that Steven Dick, K1RF made a PDF with 4 potential problems named "QMX inspections and potential issues.pdf" in the thread mentioned above.  

Some close up's

 

After installing the connectors, I found out that I had to cut a bit of the female headers pins to prevent shorts on the buck converters. The 2x3 female header connector was touching the C10? next to D103. I didn't see this on the images in the QMX manual but maybe the connectors where from another brand.  

Then they could be soldered without any problem. 

It's starting to look good.

Control board

For some reason I started on the Control board instead of the LCD board. But luckily they don't really depend on each other.

So I continued on Section 2.22. The images 3 and 4 in the manual show construction of the QMX-Mini control board, but the idea is the same.

I placed the header in the main board connector, gently pushed down plastic part of the header down until it was on the female header. Then i placed the spacer PCB on top of it.

On top of that I placed the control board PCB and soldered the pins. 

I cut the pins pins as described in the manual, but then found out that the rotary encoders didn't fit. So I used a DIY deburrer to upsize the holes a little and after a few passes the rotary encoders fit.

To bend the rotary encode pins I didn't use a screwdriver as stated in the manual, but used a small metal ruler. 

 And even then, I managed to brake 2 of the rotary encoder legs, just like I did on my QCX-Mini. :-(
But nothing you can't fix with a few small pieces of wire.

Both encoders are in place 

And the tactical switches and microphone are soldered in place acording to section 2.24 and 2.25 of the manual 

And the 11mm nylon hex spacer are installed (don't forget to small space PCB). 

In the PDF Steven Dick, K1RF made mentioned in the thread  above, problem number 4 points out to a problem that there might be a contact between left rotary encoder and the center pin of the power connector. In my case there was enough space to prevent contact (I even wiggled the control board and no shorts where made). But again it's worth checking as Han pointed it out in his manual : Section 2.31 - point 3. .

Thanks again to Kees K5BCQ for reminding me to include this info. 

So far so good.  

LCD Display

The installation of the LCD board is described in the manual under section 2.18. And after aligning the LCD display to the LCD board PCB connections are made using the previous saved component cut-offs (our you could use silver plated 0.6mm wire like I did). 

The 2x5 header is soldered into place. 

The four 11mm nylon spacers (bottom view)

And after modifying the 20K trimmer potentiometer R47, it is soldered into place. 

 

After installing the LCB PCB on the Mainboard I the control board was plugged in. 

Spoiler: I made a big mistake, can you spot it?

Happy with the result so far, but now it's bed time. Tomorrow I have a day off and going to do the final check before the smoke test.

Smoke test

Next morning after a good breakfast, it was time for the final inspection. Under my microscope I checked all soldering spots, missing SMD components etc. And when all looked good, it was smoke test time.

I setup my power supply to 7V with a current limit of 250mA, connected the USB-C cable, applied power and nothing to see and more important nothing to smell.

My power supply indicates a nice 0mA and after pressing the left rotary encoder, aprx 140mA of current was flowing. My computer indicates that a new Flashdrive was found with the name QMX, indicating that the bootloader was working. NICE.

There was nothing on the display, so I turned the display contrast variable resistor and a row of blocks became visible. As the QMX doesn't have any firmware installed, this was to be expected.

 

I copied the already downloaded QMX firmware (1_00_009.QMX) on the QMX drive and after a few seconds the drive disappeared. 

And then the waiting started, but nothing changed. Power supply just indicates the same current, display stayed the same. Did I do something wrong?

I switched off the power, applied it again, pressed the left button, the expected current was drawn, but still nothing on the display. No QMX flash drive was show, so the firmware should have been installed correctly.

Then I remembered that the QMX has like the QDX a serial interface, so I started a terminal window, executed dmesg to see if there are any kernel messages , and there it is. ttyACM0 is there. So it should be alive. 

 

I started up minicom -D /dev/ttyACM0 and Houston we have a connection.

So it's alive. I walked through the menu, did some Diagnostics (menu Hardware tests - Diagnostics) and as shown below, everything looked OK. 

So it must be a hardware thing.

I switched off the power supply, and took the QMX apart (removing the control PCB and LCD PCB).

Took a good look at all the pins of the connector which connects the LCD PCB to the main PCB and all looked good.
Eh wait what, connector? The LCD PCB has 2 connectors, one 2x5 pin and one 2x2 pin :-(

Well that explains a lot, that 2x2 connector is quite important. As shown below, it supplies GND, RS, RW and controls the backlight.

I soldered the 2x2 header on the LCD board, put everything together again and . . . 

YES. 

Next step, starting minicom again, and see if all the filters are doing there job. 

But first. . . . some house cleaning and lunch.  

How much does it throw?

Using my OZ2CPU digitale RF mW-dBm-mV meter in combination with the -40dB RF Sampler I measured the power output for the various bands.

 The power outputs where (for 9V):

• 80m - 4.57W
• 60m - 4.58W
• 40m - 4.68W
• 30m - 4.56W
• 20m - 3.89W

Although 20m is a bit low, for now I'm happy with the results.

Boxing it up

The last step for this build was boxing it all up. And for that I followed Hans his manual section 2.29.

 It all started well and 

But I couldn't get the Display board to slide over the Control board. So I had to take everything apart again.

Looking for the problem, I found out that the control board initially could go through the Displayboard, after installation of all the components, it didn't :-( 

So I took out my files and filed out the area in the Display board where the Controlboard should come through and after a few minutes making room it fitted. 

And the rest of the enclosure could be fitted.  

First time FT8

On a day off I took time to put the QMX onto the air with WSJTX. And after decoding a bunch of FT8 QSO's it was time to make some of my own.

40m

20m

Conclusion: it works ;-) 

Until now

Having this QMX all boxed up and ready, measured the output power, made a few FT8 QSO's  there are only a few things left to do :

• Add Tilt feet  as I made for my QCX-Mini.
• Find out why the 20m more then 0.6W lower then the power output on other bands (DONE).
  Update: after reading this, OM Mike W1MT took the time to fill in my contact form and wrote : 
           "QMX low power on 20m. Compress (squeeze) the turns on L513 to gain 20m power. -mike/w1mt"
  Thanks for the pointer Mike, much appreciated and will give that a try.  
• Read up on the article on QRP-Labs website about the 20m sensitivity modification.
• Do more hardware tests to see if the bands and sensitivity is are all ok. 

 

My tips

Some tips I would like to share: 

• Don't work on the QMX late at night.
• Read the manual (twice) before soldering.
• Take regular breaks with a beverage of your choice (alcohol based beverage, may seem to relax, but also might cloud your skills). 
• Read  the PDF Steven Dick, K1RF made  with 4 potential problems named "QMX inspections and potential issues.pdf" in this thread.  
• Become a member and read the posts on the QRP-Labs groups.io group. 
• And above all, take your time when building kits. Remember, it's not a race who finished it first, it's a hobby to enjoy. 

 But these tips are just the tip of the ice berg.

Check out these tips from Hans : 

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