QRP Labs QCX – BaMaTech Enclosure


Since PCB revision 5, a cat port has been incorporated on the PCB. As it’s already a tight fit, I mounted angled pin headers on the underside of the PCB.


The BaMaTech enclosure was not yet featured with an opening for the cat port. I had to drill a new hole to fit a 3.5mm stereo socket.


Now that everything is fitted in the enclosure, it’s time to do the final alignment of the QCX. I’m not going to elaborate on this, everything is described in detail in the manual. Just make sure you use a non-conductive anti-static tool when you do this.

Below you can admire the finished result πŸ˜‰


Top view with custom splash screen.


Front view.


Back view.


Right side, with added cat port on the bottom left.


Left side.

QRP Labs QCX – Putting It All Together

Now that the most difficult part of the project is done, we can start soldering all other components to the board.


Take a look at my little workbench where I have all the tools I need to put the kit together.

20200125_205044 20200126_133505

To save space on the board, all resistors, inductors and capacitors are mounted vertically. I’m using a my round tweezers to bend the leads. This way they are all bent the same way.


every component, and every soldering was checked after soldering. For this I use a magnifying glass for the visual check and a multimeter to check the connection.

Some of the tools I used for this project can be found on AliExpress.

The AN8008 Multimeter. 40X Full Metal Jewelers Folding Magnifying Glass with LED. Set of precision tweezers. PCB assembly stand. Heat resistant and anti static silicone soldering pad. Side cutting pliers.

QRP Labs QCX – Winding The Toroid

The first thing you need to do with this kit is to wind the toroid. You can do this by clamping the toroid between thumb and forefinger and wrapping it like this.


There is however, a better way to do this. By clamping the toroid in your vice like shown in the pictures below.

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This way you have both hands free to make nice firm windings. Don’t forget to check regularly how many windings you have already made. The toroid must be wound exactly according to the schedule given in the manual.

When counting the windings of a toroid, one should count the number of times the wire goes through the center of the toroid. This however can be very difficult as the toroid is rather small and there is not much space to easily count the number of windings. Another option is to count the number of windigs you can count on the outside of the toroid and add 1. That should give you also the correct number of windings.

in the end you have to get something like this. Isn’t it beautiful?


QRP Labs QCX – What was in the box?

When the package arrived from QRP labs (less than 15 days after shipping), it was immediately clear our customes had a look a the content.


Upon opening, everything looked just fine. Nothing was missing and all still nicely wrapped in bubblewrap.


2 bags, 1 with the main parts and one for the band pass filter. For This built, I’ve choosen the 40m band.


Let’s start building this thing!

QRP Labs QCX – Why Building a CW Transceiver?

I always wanted to be able to decipher Morse code. Even before I had my basic license, I had already started learning the Morse alphabet. And you can take that literally. I never got much further than “starting”.

According to my excercise book, I started for the first time in October 2015. I kept it up for two weeks then. In May 2016 I made one excercise, in March 2017 two. I restared in December 2017, again for two weeks. Then again, did one excercise in November 2018. I can assure you, you won’t learn it that way.

Probably I was too busy discovering the many other aspects of the hobby. SSB, PSK, RTTY, FT8, building magnetic loops and Automatic Magnetic Loop Controllers. It wasn’t until I got a little tired of all that, and noticed couldn’t use half of the spectrum I was given, that I made the click: I was going to learn CW. This time for real!

Since October 2019 I have been doing a 10-minute exercise every day. For this I use the app of IZ2UUF. In total I only missed about 5 days. And that is all you really need to learn CW: practice and dedication.

Maybe you also need something else to stay motivated, such as rewarding yourself with a transceiver that you can put together yourself and with which you can further practice your learned CW? A QCX perhaps?
There you have it, the reason why I bought and built the QCX.

Flashing QCX Firmware using a Teensy 3.2

Today, I wanted to flash my QCX qrp transceiver with the latest available firmware. But I didn’t have an AVR programmer at hand.

In a tutorial Simon VK3ELH describes how to use an Arduino UNO to program the QCX. Unfortunately I don’t have an Arduino UNO neither. What I do have are Teensy 3.2, and seems to be, you could use those too.

I’m asuming you already had the Teensy 3.2, so you most likely also already installed Arduino and Teensyduino. Open a new sketch and go to File -> Examples and look for ArduinoISP. Connect the Teensy 3.2 with a usb cable to you computer, select the appropriate board (Teensy 3.2 / 3.1), press verify and upload the sketch. You should not get any errors, no codechanges are needed.

Next you wire up the Teensy 3.2 to the QCX according to the following schematic:

Use your Teensy 3.2 to flash new firmware in your QCX

Check the QRPLabs@groups.io forum to find out where you can download the latess firmware. In this example it’s version 1.04.

To flash the new firmware to the QCX, you need a program called AVRDUDESS. You can find it here.

Start the program and change the following fields (those traced in red)

  • Select β€œArduino” as the programmer (There is no Teensy 3.2 in the list)
  • Select the COM port the Teensy 3.2 is connected to
  • Enter BAUD rate 19200
  • Select ATmega328 as the MCU
  • Select the path where the new firmware is located
  • Press the Program button.
Use AVRDUDESS to flash new firmware in your QCX

30 seconds later your QCX is flashed with the latest firmware. Have fun!

Automatic Magnetic Loop Tuner – Arduino 1.8.11 & Teensyduino 1.50

I just installed the latest version of Arduino: 1.8.11 and Teensyduino 1.50.

When compiling the latest version ML_v409 I got the the following error:

ML_v409:1287: error: 'class ADC' has no member named 'setSamplingSpeed'

Apparently something changed in the ADC.h library so we need to change the following code:

// Set up the two separate ADCs for synchronous read at 12 bit resolution and lowest possible measurement speed (minimal noise)

adc->setSamplingSpeed(ADC_SAMPLING_SPEED::LOW_SPEED, ADC_1);
adc->setConversionSpeed(ADC_CONVERSION_SPEED::LOW_SPEED, ADC_1);
adc->setResolution(12, ADC_1);
adc->setAveraging(16, ADC_1);

  to this:

 // Set up the two separate ADCs for synchronous read at 12 bit resolution and lowest possible measurement speed (minimal noise)

Then recompile again and you are good to go!
This info was also already shared in the LoopController group on Groups.io

73 de ON5IA

Magnetic Loop – Capacitor Box

After building several tuners it was time to build a magnetic loop that I could set up outside in my garden.
I built a magnetic loop for the 80m band to the 30m band.
The magnetic loop has a circumference of 6 meters and a diameter of 1.9 meters. The material I used is 2.2cm copper tubes used in sanitary installations.
Visit the 66pacific.com website to calculate your magnetic loop.

To get the loop into resonance on the frequency we want to use it, we need to add a capacitor. For this antenna, I chose an air variable capacitor. The capacitor was made by HA8DU and bought via a Dutch reseller.

Magnetic Loop Air Variable Capacitor

The capacitor is controlled by a Nema 17 stepper motor., which on his turn is connected to the automatic magnetic loop tuner.

Magnetic Loop Air Variable Capacitor

On the capacitor, I’m using a 60 teeth GT2 pulley, and on the stepper motor a 16 teeth GT2 pulley. The belt is a GT2 280mm rubber band, reinforced with fibreglass. Do not use a belt with steel wires.

Magnetic Loop Air Variable Capacitor

To connect the capacitor to the loop I used soft copper bands and fastened them with hose clamps.

Magnetic Loop Air Variable Capacitor Magnetic Loop Air Variable Capacitor

If I would have to make this loop antenna again, I would switch the positions of the tube clamps and the hose clamps. Also, would I turn the capacitor 90Β°. But now, for the moment, this is fine πŸ˜‰

Magnetic Loop Air Variable Capacitor

All closed up. Next step is to tape the box with Duct Tape and make sure all other holes are sealed with silicone. Then I’ll paint the loop black and search for a better way to attach the coupling loop.

AliExpress parts list:

Nema 17 stepper motor bracket:

Nema 17 stepper motor 45 Nm, 1.5A:

GT2 Pulley 16 teeth:

GT2 Pulley 60 teeth:

GT2 Rubber Belt:

Automatic Magnetic Loop Tuner – New Firmware Available

Loftur TF3LJ/VE2LJX released a new firmware version for the Automatic Magnetic Loop Tuner. You can find it at the bottom of his web page: https://sites.google.com/site/lofturj/to-automatically-tune-a-magnetic-loop-antenna

Firmware version 4.09 fixes stepper motor hiccups that might occur when you move the stepper motor a lot at high speed forward or backwards.

The PCB’s I designed earlier for the DRV8825 or A4988 stepper motor drivers are compatible with this new firmware. I recommend upgrading to this new version if you are using one of mine PCB designs. In the rare case where you would encounter issues, you can always revert back to firmware version 4.08.

Automatic Magnetic Loop Tuner – Smaller Enclosure Finished

When our first batch of automatic magnetic loop tuners was finished, I started looking for another enclosure. One that was sturdier, better looking and cheaper. I ended up looking on AliExpress and found this aluminium box. After some measuring, drilling and filing I test fitted the components.

I quickly understood this enclosure would be a very tight fit. Using the bulkier rotary encoder together with the larger tin box for the SWR bridge was not possible. In parallel, we started working on our second batch of automatic magnetic loop tuners, and I needed the buttons and screen bezel to finish another tuner. Having no spare screen bezel any more and in need of extra internal space, I ditched the screen bezel idea and let the LCD come out of the enclosure. It wasn’t even looking that bad.

Automatic Magnetic Loop Controller

Yet, the little extra space I gained on the inside of the enclosure was still not enough to fit the SWR bridge in it’s RF shielded tin box. I had to go and find a smaller box, which I did on a local ham fair.

SWR Bridge
SWR Bridge in small enclosure

The SO-239 connectors were also replaced by SMA connectors. These are also a lot easier to mount as you only need to drill one round hole.

SWR Bridge

When I made the A4988/DRV8825 version of the automatic magnetic loop tuner PCB, I made it exactly 100mm wide. This way it fits nicely in the PCB slot in the aluminium box. When the PCB is positioned completely to the left against the tin box of the SWR bridge, there is plenty of room for the rotary encoder on the right. The rotary encoder is positioned between the power button and the fuse and serial connector.

Automatic Magnetic Loop Tuner

When the box is closed and the power is switched on it looks very nice πŸ˜‰

Automatic Magnetic Loop Tuner

The knob on the rotary encoder is a full aluminium knob which you can find here on AliExpress.