Tag Archives: QRP Labs QMX

Woo hoo! Finally taking my QRP Labs QMX on a POTA activation!

Those of you who purchased a fully-assembled and tested version of the QRP Labs QMX are, no doubt, patient people.

While you can order a kit version of the QMX and receive it fairly quickly (still, I believe), the assembled versions take more time as the QRP Labs crew is small and they build and test these by hand.

I ordered mine on June 5, 2023, and it shipped on December 27, 2023.

Truth is, I’ve had a QMX kit since Hans Summers announced it at Four Days In May (FDIM) prior to the 2023 Hamvention. I’ve been meaning to build it but, as many of you know, my life has been a tad crazy these past months and I never got around to it.

I purchased an assembled version of the QMX because I will be reviewing this one and wanted a factory-tested unit. I would have never guessed I’d receive the assembled unit before building it!

Familiar Form-Factor

The QMX looks so much like my QCX-Minis, I’ve gotten them mixed up in the shack! The menu system is very similar to the QCX, but there are some changes to accommodate band changes, modes, etc., as the QCX-Minin series is mono-band CW only.

The QMX, on the other hand, is a five-band, five-watt, multi-mode (CW, Digital, and likely SSB in the future) transceiver. It’s hard to believe you can purchase the QMX for as little as $90 (bare-bones) kit or $165 (fully-assembled and tested).

I initially thought I had an issue with my QMX because it kept shutting down the transmit function. Turns out, that was all user-error. I mentioned the issue on an episode of the Ham Radio Workbench podcast, and a couple of listeners wrote to tell me what I was doing wrong: I was feeding it too much voltage. The QMX doesn’t want more than 12V or so. If the radio detects even a temporary mismatch, it shuts down the TX to protect the finals, etc.

I was unintentionally triggering the QMX’s self-protection functionality!

Once I figured that out, I decided to simply pair my QMX with my Bioenno 3Ah 9V LiFePO4 battery. That would yield about 3 watts of output power and be a comfortable voltage for the QMX.

Vance Historic Birthplace (US-6856)

On Thursday, March 7, 2024, I finally took the QMX outdoors where it belongs! I had a one-hour window of time to complete a full activation. I decided to pair the QMX with my Chelegance MC-750 vertical.

My QMX is a “low-band” version that covers 80, 60, 40, 30, and 20 meters. I thought the top end of its band coverage would serve me best mid-day, so I planned my activation around 20 meters.

Setup was easy and simple. You can see the full set-up process in my activation video below.


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On The Air

I hopped on the air and started calling CQ POTA after sorting out my QMX settings–I needed to adjust the sidetone and I had to take it out of split mode! Continue reading Woo hoo! Finally taking my QRP Labs QMX on a POTA activation!

QMX – From Kit to Field!

by Matt (W6CSN)

The Radio

The QMX by QRP Labs is a five band, multi-mode radio introduced by Hans Summers G0UPL at FDIM in 2023. The QMX is the next logical step in the radio development journey at QRP Labs, bringing together the innovative approach to FSK modes like FT8 from the QDX and the CW performance of the QCX series. This is all done in same enclosure as the QCX-Mini which is not much larger than a deck of playing cards.

Size of the QMX compared to standard deck of playing cards.
The QMX is about the size of a deck of cards.

The keen observer will notice that the QMX also sports a built-in microphone which, along with associated circuitry, supports future introduction of voice modes by way of firmware update. Other notable features include SWR metering with protection as well as solid-state “PIN” diode T/R switching, plus the option for “high band” coverage of 20 through 10 meters in addition to the original 80m-20m version.

Most hams have, at one point or other, forgotten to throw the antenna switch, adjust the tuner, or even connect an antenna before transmitting. The SWR meter and protection really sets the QMX apart from earlier QRP Labs radios. There are plenty of sad tales on the QRP-Labs forums from QCX or QDX users that “smoked” the BS170 mosfet finals in a moment of operating into a badly mismatched load. It’s remarkably easy to do, ask me how I know!

The Build

Based on experience with the QCX-Mini and having put together several QDX’s, I admit to being hesitant to starting assembly of this radio. The level of integration in the QMX as a multi-band, multi-mode unit is probably the highest yet to come out of QRP Labs. The components that were merely small in earlier radios are absolutely tiny in the QMX, specifically the LPF toroidal cores. The main board, internal switching power supplies, display, and controls board are all sandwiched together in a tight fit for the custom enclosure.

photo showing a partially completed circuit board
Most of the electronic components installed on the main board.

The build started with a slow and methodical approach of doing a little bit each day and working in the morning when my mind was fresh and there was good light on my workbench, a.k.a. the dining room table.

The first “disaster” happened when performing the factory recommended modification to Revision 2 boards shipped in 2023. The mod calls for a protection diode to be installed across a SMD mosfet. Several leaded 1N4148 diodes were available in my “junque” box so I attempted to carefully fit one of these in the right position on the board. While soldering the diode in place I managed to lift C508, a microscopic .1uF SMD capacitor, clean off the board!

photo of circuit board with modifications
The suggested modification adding a protection diode.

Given the tools at my disposal, there was no way I was going to be able to get that capacitor back into place. Therefore, I grabbed a standard through hole .1uF cap and painstakingly got it connected in the right place, verified by lots of continuity testing.

Once finished with all the electronic components on the main board, I was feeling pretty cocky and also the completion of the project was more clearly in view. The cautious and methodical approach gave way to a faster build pace, which directly lead to the second “disaster.” While installing the headers that connect the main board to the display board, I failed to CAREFULLY READ THE ASSEMBLY MANUAL and soldered the male pin headers where I should have installed the female sockets!

This misstep might have ended the project right then and there if I had not at some point in the last year bought a proper desoldering tool. This is not an expensive automatic vacuum pump powered solder re-work stations, but rather a heating tip and manually actuated solder sucker built into one tool. Twenty-two unsoldered connections later, we were back on track. Continue reading QMX – From Kit to Field!

POTA Field Report: Andrea Activates Two Iconic Cold War Sites

Many thanks to Andrea (IW0HK) who shares the following field report:

Cold War POTA in Berlin

by Andrea (IW0HK)

In the last week of October, I found myself in Berlin for a work commitment.

Taking advantage of two half-days off, I wanted to combine two of my great passions: radio and the history of the Cold War. I chose to visit two historical sites that also serve as a reference point for the POTA (Parks on the Air) ham radio program, allowing me to transmit with my radio in these unique locations.

The first location is a park located about a kilometer away from where I worked for a week, the headquarters of RBB, the public radio and television of Berlin and Brandenburg. This park is Teufelsberg, which literally means the Devil’s Mountain. It is an artificial hill in Berlin, created using the rubble from World War II, located within the Grunewald forest (POTA reference DA-0218).

On this hill, the Teufelsberg listening station of the American NSA in Berlin was situated, which was used to intercept radio signals from East Germany during the Cold War.

Today, you can still see the remains of the antenna covers of the listening base. I activated the Pota park that has been established around the abandoned base, and I was delighted to transmit my signals in Morse code (CW) in QRP mode in this historically significant place.

I used the small QMX transceiver from QRP Labs, a gem for operating in FT8/CW modes on the 80/60/40/30/20 meter bands.

For an antenna, I used a 20-meter wire connected to an EFHW 49:1 balun, hung above a tree. Amid families flying kites, I made 15 CW QSOs, which allowed me to validate the park activation. The program requires a minimum of 10 QSOs for activation to be valid.

The second activation took place in another symbol of the Cold War: the runway of the former Tempelhof airport. I activated this as a POTA site and transmitted CW QRP with the small QMX transceiver from QRP Labs in the fog and cold.

The Berlin-Tempelhof Airport was an airport located in the southern part of the central Tempelhof-Schöneberg district and was operational from 1923 to 2008.

It is famous for hosting the Berlin Airlift base (1948-1949), which was an incredible operation undertaken during the Cold War by the United States and their Western European allies to transport food and other essential supplies to West Berlin, surrounded by the Soviets.

Today, the airport is closed, and its runway has become a massive park (POTA reference DA-0169) used by Berliners for various outdoor activities. I activated it early in the morning on a gray and cold day, setting up my EFHW antenna practically on the runway.

Again, I used only CW, and in no time, I reached the number of 11 QSOs. The cold made me stop the activity earlier than planned, but the activation is still valid. After concluding the transmissions, I walked through the enormous park, imagining its past use and appreciating how often my amateur radio passion leads me to incredible places.

This was the first test of this “minimal” POTA kit with the QMX transceiver, the 20-meter EfHw antenna, and the XTPower XT-16000QC3 12v power bank.

I must say that the test was successful. This is an excellent little radio that I want to use and take with me on every work trip. The POTA program continually takes me to incredible places, both in terms of nature and history, as it did in this case in Berlin

Field Kit Gallery: KM4CFT’s QRP Labs QMX/QCX-Mini Go Kit

Many thanks to Jonathan (KM4CFT) who shares the following article about his portable field radio kit which will be featured on our Field Kit Gallery page. If you would like to share your field kit with the QRPer community, check out this post. Jonathan writes:

Hi Tom,

I thought I would share the two go kits I have. I tend to customize my equipment and supplies before I go on a POTA or SOTA outing but I keep these for the rare occasion when I want to grab a radio real quick. [The first on is my] QRPlabs go kit:

The kit is for my QRP Labs QMX/20 meter QCX mini. It contains everything I need to operate 20 meters CW.

The case is a regular Lowepro case that I got with my KX2 when I purchased it from another ham. I did not realize it came with it so I accidentally ordered an extra from Elecraft which I now use with the KX2 kit [featured in a future Field Kit Gallery post].

The kit uses many components from K6ARK, including the 20 meter EFHW antenna and the retractable paddle.

The battery is a TalentCell from Amazon. I use it because it supplies 12v instead of 13.8v. One of the downsides of the QMX is that it cannot handle 13.8v, so I have to stick with 12.

I keep a cheap pair of earbuds with me just in case but I try to bring a nicer pair of headphones whenever possible.

Hopefully this information is useful to you and your readers!
-Jonathan KM4CFT

Readers: Check out Jonathan’s YouTube channel by clicking here.