One of the best ways to learn about radios is to build your own, even in the age of cheap SDR dongles. [Aniss Oulhaci] demonstrates this with a simple HF SDR receiver built on a breadboard.
The receiver takes the form of a simplified Tayloe detector. An RF preamp circuit amplifies the signal from a shortwave antenna and feeds it into a 74HC4066D analog switch, which acts as a switching mixer. It mixes the input signal with the local oscillator’s I and Q signals to produce the intermediate frequency signals. The local oscillator consists of a SI5351 clock generator with a 74HC74D flip-flop to generate the I and Q pair. The signals pass through a low pass filter stage and get amplified by an LM358 op amp, resulting in the IQ signal pair being fed to a computer’s stereo sound card.
An Arduino is used to control the SI5351 clock generator, which in turn is controlled by the same program created for the SDR Shield. With the audio signal fed to HDSDR, [Aniss] was able to pick up a shortwave radio broadcaster.
While this is by no means a high-performance receiver, building an SDR on a breadboard is still a great weekend project, with plenty of potential for further experimentation.
The Tayloe mixer derives from the commutating filter. I saw the filter in the first ham magazine I ever saw, QST for April 1971. And while I saw later articles promiting the concept, I don’t remember any projects that used it. Until the Tayloe mixer. And I’m aware that something nagged at me along those lines, even if I didn’t quite see it.
The magazine can be found here: worldradiohistory.com/Archive-DX/QST/60s/QST-1971-04.pdf
pages 18-23. Tayloe sure did implement it differently!
Yeah, the so-called Tayloe mixer is just a commutating mixer, or even more simply, just two switch mode mixers in quadrature. It has existed for years. The first I saw it was in analyzing a WW2 radar gun-sight in university 50 years ago.
Also the SI5351 clock generator can generate I&Q signals directly. No need for the div by 4 flip-flop.
The first time I saw this circuit, it was the “Softrock” SDR. The biggest difference – the old version used the si570 oscillator.
The 5351 needs an external oscillator source. Generating I and Q signals directly would be nice, but requires a significant rewrite of the code.
The SDR Cube worked the same way but was able to do reception (and transmit too!) using a dsPic. I wonder if any of the inexpensive chips like today’s esp32 or Raspberry Pico chips have enough oomph to do the same?
Soon i will upload a video on raspberry pi pico sdr with scope oled ! And also faster processing rate
In the past you built a receiver from individual parts now it’s use a ready made microcontroller may ad well buy a dongle
This isn’t so different from an early SDR project, maybe in the ARRL Handbook, that I saw. Two mixers, and a soundcard.
You can’t build SDRs from complete scratch. Your way has people stuck in 1966, ignoring 55 years of innovation.
As a German SDR dev said in 2016: It is better to see a waterfall plot where the action is that hopping blind through channels.
*than
Edit function much needed :(
At this piunt its becime a sort if language of ut’s owm…
Ja, schon.. On the other Hand, if all Operators do keep waiting for some Action because they don’t see anything going on in the Wasserfalldiagramm, then nothing will happen. ;) Vy73/55
That’s unnecessarily harsh — there’s a spectrum of integration from mining minerals out of the Earth to buying a commercial ready-made product. A hobbyist can pick any point on that spectrum, and have some fun building.
The receiver of the past you refer to is admirable, though likely wasn’t built on a quadrature mixer, and probably didn’t have the frequency agility afforded by using a PLL like the Si5351. It’s good to build a PLL from discretes once (though, haha, who are we kidding, who builds them out of discretes ;-). People cheat, and use 4046s and call it discrete!). But once you know the rudiments, it’s fine to scale up, and no one should lose cred for doing so.
But Mark isn’t completely wrong, either.
A while ago, someone told me that he/she “built” a power supply himself/herself.
In my mind, I saw picturedls of a big transformer, fat diodes for the bridge rectifier, an 78xx series stabi, cooling fans, heatpipes , a selfmade chassis created from metal plates with a saw, held together with screws and so on.
But how was reality?
A bunch of commercial PSU modules stacked together with zip ties.
Yeah, homebrew.. Hm.. I wasn’t prepared, as it was/is not exactly my definition of it.
PS: And yeah, I’d love to be self-sufficient. I’d love to acquire the skills to make wires from metal all by myself or the help of friends. That would be the next big step to “real” homebrew for sure.
Tipp: Replace that RF preamp by an amplifier based on a battery tube.
In Germany, we used to use EF97, EF98 (ex car radio tube) or EF95.
The big advantage is that tubes can handle strong signals without failing/going blind.
Instead, they go softly into saturation mode.
Just think of a battery tube as a rock-solid FET.
Trust me, I’m speaking from experience.
It’s not rose-glassed nostalgia! Give it a try!
I used to use an EF95-based SDR (fixed XTAL) with Dream software in the 2000s long before it was cool.
I was a young teenager when I tinkered with them, no “old fart” or angry white man. No boomer, either!
Tubes can handle long wire antennas and aerials with a high voltage/current much better than anything else.
Here are some links:
Mr Kainka’s tinker box pages (he’s a book author):
http://www.b-kainka.de/bastel96.htm
http://www.b-kainka.de/bastel97.htm
http://www.b-kainka.de/bastel100.htm
http://www.b-kainka.de/bastel101.htm
The Elexs experimenter page:
https://www.elexs.de/ef956.htm
Schematic:
https://www.elexs.de/ef9554.gif
Check out the designs of Charlie Morris on YT. He’s been messing with breadboarding’s SDR for a while now
Nice video, but I’m afraid it is a bit of an old-fashioned fantasy. It would be nice to think that our beloved analog mixers and direct conversion receivers still have a place in the SDR world. That may have been true a few years ago when we were using soundcard-based SDRs. But today we just put an Analog to Digital Converter at the antenna, do “Direct Sampling,” create a digital stream, and sent it to the CPU for processing, right?
Sometimes we think that we can show younger people how our older tech (Direct Conversion receivers) is STILL relevant in the age of SDR radio. But I can just hear them scoffing at this notion, pointing out that I,Q-to-soundcard front ends have gone the way of the dinosaurs, and all we need now is an ADC and a CPU.
But hey, I am an HDR guy. Am I missing something here?
still curious about the ‘software’ part; is this like QAM or even related?