We all know QRP Labs, purveyors of QRP kits, headed by QRP Hall of Fame member Hans Summers. They’re known primarily for the QCX and its variant, the QCX+ and QCX Mini. But today, Hans released a new product that’s sure to shake up the QRP Digital world: The QDX, a four band QRP digital transceiver that offers higher performance and greater features than competitor’s single band rigs, and at a lower price. But that is only part of the story.
The QDX is a performance power house, as it’s a full SDR transmitter and receiver with built in… everything. Everything is solid state (no relays) and all communication with a PC is done via USB- no digital interface needed. A high performance USB audio adapter is built into the QDX so there are no audio cables required either. As with the QCX, the QDX has its own test equipment built in, but not on a 16×2 display. The test routines, configuration, and debugging is all done via a serial console. No drivers are needed! This will be perfect for those wanting to integrate the QDX into a Raspberry Pi based portable build.
The QDX outputs 5 Watts at only 9 Volts, but can also be built to work fine on 12-14 V. What’s interesting is that this is a pure SDR, and does not contain an SSB exciter found in other digital-only phasing rigs. The QDX modulates the tones directly by measuring, and then adding the tone being sent to its built in sound card with the transmit frequency. There’s no modulation per se, it just outputs the tone directly from the si5351a. Very neat stuff!
The QDX will work on 80, 40, 30, and 20 meter bands. For now it’s not possible to put it on different bands, but QRP Labs’ iterative approach to design indicates that this may be a future possibility. Time will tell. But lets be honest: If this were a single band rig, we’d buy it and be just as happy 😉
Check out the QDX on QRP-Labs.com/qdx and the video below which explains far more than what I’ve posted here. It goes on sale on 10/11/21 for $60, plus $20 for an optional aluminum (aluminium?) case. You can also read the official announcement on the QRP Labs Groups.io page.
Also, if you haven’t already, subscribe to the MiscDotGeek YouTube channel. You can be 100% sure we’ll be doing a build series on the QDX just as we did for the QCX Mini. Stay tuned!
I love the tool sets they build into their products…
I agree Paul, the features included in such a low cost device are astounding.
I just got finished building a 20m QCX+ and had resolved to just buy the damned things pre-built; I hate winding toroids with a passion. But I really want this thing.
The antidote to hating toroids is to wind more of them. The T1 on the QCX (L12 on the QDX) is a bit of a pain, but the rest are like sewing 😉 The trick is to take your time and use magnification to check your work. The QDX will be great, I can’t wait to get one too!
Han did supprise us again. Didn’t see this coming, but think a lot of non CW ham’s will like it. I’m going to order one when it comes out.
This is Ham Radio’s future! No mic or key or audio out. Bump the power to 20 watts and use a mag-loop antenna(computer-controlled also). World wide communications and the neighbors never know!
I keep my computer and radioing vrry separate and will never give up my CW QRP. But this is the future.
RTTY is sent by frequency shift keying. Shifting between two different frequencies, originally 850Hz apart, later 170Hz apart. So you switch in capacitance to a crystal or LC oscillator to lower its frequency.
Once SSB was good enough, you could put a pure audio sinewave into the microphone jack, and get a CW signal out of the transmitter. Use an audio oscillator switching between two audiofrequencies, and you get FSK, frequency shift keying, out of transmitter. Unless the SSB transmitter is poor in design or adjustment, or the audio oscillator is not a pure sinewave, you can’t tell how the CW or FSK signal is generated.
These new modes are a variation of that. If the software generated a quadrature output it would be really easy for a phasing rig. But they expect an SSB rig, so for a phasing rig the tones have to go through an audio phasing network first.
There’s no magic here. It’s the way things used to be. But unless a rig has an FSK input, most won’t modify their rigs, so audio is the only means.
So if you want to use a simpler method, like here, you have to take the tones from the software, decode them so you have distinct levels representing each tone, and then shift the rig’s synthesizer between four (is it four?) distinct frequencies.
Be patient on the build, and do one toroid an evening for several days… Make sure your kids are not around and let the profanity flow…. Both things help greatly. Wish some day that hams stopped worshipping toroids as they are often not even the best solution for an inductor in many cases that they are used for…. one can hope. 🙂
The QDX measures the zero crossing of the incoming tone (by oversampling the incoming audio) to determine it’s period (and therefore frequency) meaning that any frequency within the audio range and (very fine on the Si5351) resolution of the LO can be generated at one time.. But ONLY one tone.. so this only works for single tone modems.
On HF this isn’t a horrible limitation.. it does (most likely) preclude PSK31 though and any definitely any modem that uses more than one tone at once like ALE.
However it doesn’t preclude any of the “incremental shift keying” modems as they use multiple shifts but only one tone to mitigate multipath on HF quite effectively. And of course, RTTY will work in this scheme too. So probably 75%+ of the most used modes are supported by this scheme.
By dropping the amplitude component entirely in the TX stream, you can do everything non-linearly in the transmit chain, and there is no way to overdrive the TX. Output power is completely controlled by input voltage on this rigs finals. It is a CW transmitter that, in frequency, follows the period of the audio input signal. (They are reciprocal, so they are directly related).
Very clever actually. I did manage to get one on order and I’ll try to report back on this .. though it might take me a while to build it with my currently impossible messed up life schedule…
If you are curious about the Si5351A being used to do FSK there are examples out there for WSPR if you look from the author of the most popular Si5351 library for Arduino.
Hans has also (claims the first in a commercial product) dropped the divide by four in this rig (and that is why there is no 160m on the QDX, a decent tradeoff IMHO) and does the IQ 90 degree shift on receive without the divider by proper software setup of the Si5351. There is information on how to do that out there as well.
Note that the TX of the rig doesn’t use IQ at all, just FSK CW controlled by the I2C commands to the Si5351A. So it’s a standard SDR receiver and a class D CW transmitter with a FSK generator controlled by the input period of the incoming audio for the software and internal soundcard on the QDX.
Hopefully this explains it but isn’t too technical.
Excellent analysis, Fred. Thanks for posting it!
Hans has also (claims the first in a commercial product) dropped the divide by four in this rig (and that is why there is no 160m on the QDX, a decent tradeoff IMHO) and does the IQ 90 degree shift on receive without the divider by proper spacebar counter software setup of the Si5351. There is information on how to do that out there spacebar counter. as well.