A Fully Featured, Fifty Dollar QRP Radio

QRP radio operators try to get maximum range out of minimal power. This term comes from the QRP Q-code, which means “reduce power.” For years, people have built some very low-cost radios for this purpose. Perhaps the best known QRP kit is the Pixie, which can be found for less than $3 on eBay.

The QCX is a new DIY QRP radio kit from QRP Labs. Unlike the Pixie, it has a long list of features. The QCX operates on the 80, 60, 40, 30, 20, or 17 meter bands at up to 5W output power. The display provides tuning information, an S-meter, and a CW decoder. An on-board microswitch functions as a basic Morse key, and external Iambic or straight keys are also supported. An optional GPS can be used as a frequency reference.

The radio is based around the Silicon Labs Si5351A Clock Generator, a PLL chip with three clock outputs ranging from 2.5 kHz to 200 MHz. The system is controlled by an Atmel ATmega328P.

Demand for the kit has been quite high, and unfortunately you’ll have to wait for one. However, you can put down your $49 and learn Morse code while waiting for it to ship. While the project does not appear to be open source, the assembly instructions [PDF warning] provide a full schematic.

44 thoughts on “A Fully Featured, Fifty Dollar QRP Radio

    1. I am actually thinking of making one. I have quite some DSP experience, but not yet with an actual ARM. Have you come upon someone who has done something along these lines already? Thinking of an IQ demodulator for SSB/AM/FM/etc. Blue pill does not have a DAC though, but perhaps PWM could be used.

      1. I’ve been dinking with the STM32F103 “blue pill” and it is a struggle to get the 12 bit a/d pumping the DSP code for a pair of Hilbert Transform FIR filters then using the PWM clocked at the full 72 MHz to drive a 2-pole rc filter. Having concerns over digital artifacts in the produced audio, I started going down the path to add a very inexpensive PT8211 stereo 16bit DAC… but w/o a I2S interface on the blue-pill I started to hack using a SPI interface and I was last heard grumbling loudly while trying to get it all working as required by the little chip. Too many chores with work, being a father, and life getting in the way… it has been a few weeks since I last had time to work on it. And my 51 year old brain loses track of what I have working and where I was at if I have to put it aside for many days so currently I am discouraged. I do think that it is doable just needs the right person(s) and there is a bit of juggling to do everything in the time needed. I was trying to reduce latency to just a few (4) sample periods. The CMSIS DSP FIR filter routine wants batched samples and there is a tradeoff between getting too few and accumulating a long stretch. Regardless, four Q.15 samples at a time did seem doable. Btw, the 12 bit a/d could do oversampling and might yield 14 or more “usable” bits of resolution. I think the while the mcHF DSP rig is using a 24 bit codec the code is only using it in 16 bit mode. That’s how their firmware was back a couple years ago, anyway. Many of us are thinking similar thoughts. :-)
        One last thing: while it seems like the STM32F103 running at 72MHz is going to way overpower compared to the ATMEL ATmega328 chip being used, I am amazed at what they are doing and have to wonder if the DSP stuff that I mentioned leaves many STM32F103 processor cycles free to do all that as well. So I’ve just been thinking DSP filter / Demodulator and little else for the Blue Pill to have to do. Perhaps I’m not savvy to the ways that they are accomplishing this but if the intent was to do all that is there and in addition do the DSP stuff… well, WOW, that seems like a LOT.!! I have yet to see if QRP Labs source is available… and looking around I’m not seeing that it is. Sad if that isn’t Open Source. If anyone knows of a repository for that code I would love to hear about it if for no other reason than to learn from a “master”.

    1. Good observation. Where did you read about it being good for pirate radio?

      Some specs:
      – Maximum power: 5 watts, you will not get very far with this power if you just use it to provide music for the masses
      – Bands supported: nothing above 17 meters (so nothing above 17ish MHz frequency), not very practical for music radio
      – No microphone connection, you already spotted that

      This is just made to be used as a small morse-code transmitter for HAMs. What’s wrong with that?

      1. “– Bands supported: nothing above 17 meters (so nothing above 17ish MHz frequency), not very practical for music radio”

        I thought you just wrote that it wasn’t good for music broadcast!
        So, which bands are does it support? E Street? Marshall Tucker?

    2. It is an Amateur radio telegraph transceiver used for communicating via shortwave bands (using the Morse code). Believe it or not, there are thousands of us doing this. {Telegraphy is the ‘sailing’ of radio}

    1. I don’t know. QRP became a thing in the late sixties, and generally that meant a direct conversion receiver with limitations and an audio image, and a simple transmitter. Either a crystal oscillator a variable oscillator that lacked a good dial and might not be too stable. For much of these fifty years, “QRP’ meant “simple equipment”.

      So this is much more featured than that. A synthesizer with readout is almost too of the line compared to past transceivers. The receiver is still direct conversion, but it gets rid of the audio image, and I assume is better than the usual direct conversion receiver.


  1. Eric QRX ?

    QCX: a feature-packed, high performance, single-band 5W CW transceiver kit, with WSPR beacon and built-in alignment/test equipment. Available for 80, 60, 40, 30, 20 or 17m bands. It has rotary encoder synthesised tuning, VFO A/B/Split, Iambic keyer, CW decoder, and more

  2. Very nice radio. Article less so. The fact that it has a WSPR beacon mode is VERY significant and probably accounts for much of the high demand. You should have mentioned that. In general, it’s a modern version of a single band QRP transceiver kit. The provision of GPS frequency and timing makes it ideal for coherent CW operation which with a low enough bit rate should allow reliable communication to the antipodes. That is not something commonly practical with most QRP transceiver designs.

    For the benefit of non-radio enthusiasts, WSPR stands for Weak Signal Radio Propagation. It is a protocol developed by K1JT, Nobel laureate Joe Taylor. The purpose of WSPR is to measure radio propagation using low power, narrow bandwidth signals. Central to operation is the need to have precise time and frequency derived from GPS. WSPR and coherent CW rely on knowing precisely when and how long the transmitter is keyed and then averaging the detector output over that window. WSPR adds error correction coding to the basic coherent CW concept.

    1. I’d have to say that the bitx40 is the closest thing you’ll get to that. 40m SSB right out of the box. Easy to modify for Upper Sideband, and as easy to connect to a PC as any other. Digital could be done for about $100 total, plus antenna-, which is another $30 or so for a 40m inverted V dipole: http://miscdotgeek.com/20m-inverted-v/ (just make it longer, 33 feet per side).

    2. It is designed for modern weak signal HF digital modes. WSPR being the most advanced mode that I know of. $50 is certainly as cheap as possible for the such a unit.

      I don’t know if QRP-Labs are making source code available, but it’s not rocket science to write your own code for the QCX using the Arduino toolchain. All the bits and pieces are common items and well documented with plenty of example code.

      The only fault I see with the design is inadequate shielding of the MCU and LCD.

      I have a LimeSDR board sitting waiting for an enclosure and the arrival of a spectrum analyzer. A major interest of mine is a part 15 compliant HF rig with antipodal range. This would have to be very low bit rate, e.g. 2 KB/day and shift bands as propagation varies during the day. Somewhat daft I will readily admit, but pretty cool if I can make it work. Still have a lot of mathematics to work through though.

    3. @Winston

      RTFM, which is *really* fine! This is *precisely* what you have asked for. The only thing missing is the software to implement your mode of choice.

      I’ve had time to read the manual and am extremely impressed! The only fault I would raise other than shielding is the use of the Si5351A instead of the B or C parts. The Si5351B implements an internal VCOX and the Si5351C will accept a reference frequency. Both cost over twice as much as the A part. Any changes to the design would make the QCX more expensive. For price-performance this is a good as it gets with current technology.

      The QCX is approximately an Arduino Uno R3 based HF transceiver with everything integrated onto a single board. It has provision for GPS which is essential to any weak signal digital mode. The choice of the A part means there is no provision for disciplining the reference XO, but adding a small varicap in parallel with the xtal should take care of that with the appropriate firmware changes. While the QRP-Labs design and firmware are proprietary, the design choices make it an excellent basis for a homebrew project. There are Arduino examples for all the key parts. I can’t see anything that prevents treating this as an Uno with a custom RF shield. The overall design is first rate.

      I would have already ordered one today, but I’ve got quite a few toys sitting idle for lack of time and my license lapsed long ago. Though at $50 I may well order one anyway.

        1. I realized this morning that the QCX is even better than I thought. The use of a socket for the MCU means that it would be trivial to use almost ANY other MCU board! One can place the MCU in an RF shielded package with ferrite beads on the leads to address the noise mentioned in the manual. The ATMega 2560 would be a drop in replacement with at most some minor hacks of the firmware to alter addresses and provide more flash for additional modes. Although not advertised as such, it is a general purpose RF shield which can be used with the MCU of your choice. For really low power consumption one could use an MSP430. With something like the STM32F479 Discovery board and some serious mathematical work I *think* you could implement SSB by using PWM and altering the key shaping and AF filter circuits. That would require considerable DSP experience, so not a noob project.

          Impossible to beat! It’s a complete functioning radio as is and a general purpose MCU controlled RF module all for $50! As furnished it is compatible with the Arduino tool chain for which there are a plethora of sketches floating around the Internet. If you don’t want to use the Arduino environment all the devices on the board are well documented with many examples available for almost any MCU on the market.. It’s an RF hacker’s dream! It’s also an excellent introduction to state of the art modern RF design. Feed the I/Q output of the Tayloe detector to an ADC on a fast MCU like the STM32F479 Discovery board, write some firmware and you’ve got $75 SDR with a touchscreen display!

          I am buying 2 even if they sit for a long time!

  3. For that price, it has an amazing set of features. The article fails to mention that each $49 purchase is for a single band only: “The QCX is a 5W, single-band, high performance CW transceiver kit with WSPR beacon, and built-in alignment/test equipment. It is available for 80, 60, 40, 30, 20 or 17m bands.

    Those who aren’t interested in using it for CW may find its use as a WSPR beacon interesting. Also, it’d be great if someone would come up with a waterproof case for those traveling, boating or camping out. They might include enough space for one of QRP-Guys antenna tuners.

    1. A good choice for a WSPR beacon would be the U3S that Hans developed. Made specifically for use as a beacon, with no receive capability. It will operate on up to 6 bands using the automatic band switching features in the firmware along with the relay switching board.
      Wes AE6ZM

  4. That word “OR” in the band list is the killer. I thought it might be a “budget HB1B without a case” but it’s not. Even for the most casual QRP-CW operating, multiple bands is pretty much a requirement.

    1. Except, other than software, making it multiband would mean adding more tuned circuits or filters. One could build it, but add a bandswitch and put the filtering off the board.

      The real limitation is whether the firmware covers all bands, or is distinct for each band. If the latter, then one has to write their own, unless it’s “open source”.

      It’s a simple rig, and making it multiband complicates it, not just multiple filters but the switch, which makes it more complicated and expensive. But that doesn’t stop the home builder from making it multiband.

      The synthesizer makes it incredibly simple.


    2. @PThompson

      If you look at the QRP-Labs website they offer the required filters, relay switching board, etc. They are designed for the U3S, but would be usable with any radio. So it can be made to equal an HB1B. But it won’t be cheaper. All those extra parts add cost. A multiband QCX would cost $200-$250 once you got it all in a box.

      The QCX is very much in the tradition of a high performance QRP rig, single band CW only. Being able to send and receive WSPR is a huge plus as you can configure it to listen for band openings to selected zones and alert you. Some programming required I’m sure but it should be relatively easy to make it trigger a GSM module to call your cell phone when the band is open to a location of interest.

      All the SW controlled items (Si5351A, LCD,etc) are available as discrete units with a bunch of example programs contributed by various people.

      Hans has apparently not yet worked out how to do firmware downloads which makes me suspect that the firmware is single band. I ordered both 40 & 20 M kits, so I’ll find out when they arrive. I always save the installed firmware when I start playing with a dev board. Even though I have other plans it can be helpful to reflash with the factory image. The boards from TI, STM, etc often have so many features in their demo program that I don’t realize I’m interested in something it does until I’ve been fiddling around for a while.

      I’d never heard of QRP-Labs before this, but after reading the manual and studying the schematic and block diagram I think it is really cool! If you’ve spent any time reading EMRFD by Wes Hayward et al the basic design elements will all be familiar. Getting a complete kit for $50 is amazing. Best of all, it doesn’t require hand soldering sand grains! I’ve got a partially assembled Softrock Rx Ensemble II sitting on the shelf because my eyesight makes it more challenging than I expected.

  5. Makes me want to get back on air after 20 years off. I still have a homebrew 80m QRP rig in the shack and can still copy 25wpm. I don’t understand most of those new terms though.

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