Making a multi-band amateur radio transceiver has always been a somewhat challenging project, and making one that also supported different modes would for many years have been of almost impossible complexity best reserved for expensive commercial projects. [Bob W7PUA] has tackled both in the form of a portable 10-band multi-mode unit, and we can honestly say he’s done a very good job indeed.
As you might expect in 2025 it’s a software defined radio (SDR), but to show how powerful the silicon available today is, it’s all implemented on a microcontroller. There’s a Teensy 4 with an audio codec board that does all the signal processing heavy lifting, and an RF board that takes care of the I/Q mixing and the analogue stuff.
Band switching is handled using a technique from the past; interchangeable plug-in coil and filter units, that do an effective job. The result is a modestly-powered but extremely portable rig that doesn’t look to have broken the bank, and since the write-up goes into detail on the software side we hope it might inform other SDR projects too. We might have gone for old-school embossed Dymo labels on that brushed aluminium case just for retro appeal, but we can’t fault it.
It’s not the first time we’ve looked at a small multi-band SDR here, but we think this one ups the game somewhat.
Thanks [Pete] for the tip!
The missing link: https://www.janbob.com/electron/TinyTen/TinyTen.htm
Fixed, thanks!
(“The missing link” indeed!)
Oregon seems to produce a lot of brilliant homebrewery. The marriage of plug-in coils with modern a SDR design is quite beautiful. Micro-Mountaineer lineage. Awesome build, Bob. Dit dit.
Fantastic! A very nice compact build.
Bob Larkin announced this project last month in groups.io/g/SoftwareControlledHamRadio : it’s similar to the popular T41 Software Defined Transceiver that’s discussed in that group (but much more compact!).
If you want a solid build guide, principles of operation, C code, and great instructions how to make your own, grab the book that the original designers Albert Peter and Jack Purdum wrote: http://www.amazon.com/Software-Defined-Radio-Transceiver-Construction/dp/B09WYP1ST8 . The code itself is at https://github.com/KI3P/T41-V12-SDT (among other forks and versions elsewhere)
Arduino code is C++
I was disappointed to see that at no point home brewed beer was involved in this project.
was so excited to send it to my FIL. but he’s a ham so this still works (:
A Masterpiece—with all the documentation ready for a Engineering Design Review.
Awesome! This isn’t a casual one-night build by no means, but this shows that taken in steps a lot can be accomplished.
Plug-In Coils! I see that as a pro, not a con. It allows for a much simpler, cleaner design.
Bravo, Bob !
I am sure I have mentioned this before while commenting here on Hack-a-day. Glancing at the schematics it seems to me this SDR uses a classic Direct-Down-Converting Commutating Detector (a.k.a. a “Tayloe Detector”); it is often called a DCSDR. Unfortunately, in this design I do not see any circuitry used to isolate the antenna from the detector. This can be a serious problem if the antenna is not properly matched to the detector because the radio’s gain and bandwidth (Q) is directly dependent on how well the antenna is matched. All of this is nicely explained in Part-1 of the seminal 4-part paper starting with the ARRL’s July/August 2002 issue of QEX magazine: “A Software-Defined Radio for the Masses” by Gerald Youngblood, AC5OG.[1][2][3][4]
One way to mitigate this problem is to somehow isolate the receiver’s input from the antenna – perhaps by using a matching network, an isolator, attenuator, or a preamplifier. Another approach is to employ an IF stage, some commercial transceivers use a 60 kHz IF (look at the block diagram of the ICOM 7300 HF+50MHz SDR transceiver). An (arguably) smaller problem with this DCSDR design is that without taking care to isolate the receiver from the antenna, the radio will radiate unwanted signals through the antenna. Finally, remember that the DCSDR in its basic form is a symmetrical device. With other words, whatever happens when the device is receiving, will also happen in reverse when it is transmitting. Having an IF stage provides you with the option to use a diplexer to avoid radiating the LO signal.
References:
[1] A Software-Defined Radio for the Masses, Part-1 – ARRL
https://www.arrl.org/files/file/Technology/tis/info/pdf/020708qex013.pdf
[2] A Software-Defined Radio for the Masses, Part-2 – ARRL
https://www.arrl.org/files/file/Technology/tis/info/pdf/020910qex010.pdf
[3] A Software-Defined Radio for the Masses, Part-3 – ARRL
https://www.arrl.org/files/file/Technology/tis/info/pdf/021112qex027.pdf
[4] A Software-Defined Radio for the Masses, Part-3 – ARRL
https://www.arrl.org/files/file/Technology/tis/info/pdf/030304qex020.pdf