Design & Build Part 2: Multi-Band, Phasing SSB, and SDR

 

Amateur radio is the ultimate hacker’s hobby. You can design, build, and put on the air your own high power transceivers. And with this homemade gear you are able to reach out directly, not relying on any infrastructure whatsoever, to connect with people all over the world. It is a thrilling experience to communicate with that long distance station using equipment you created, where you know at that instant what every single transistor is doing as you key down the mic.

In a previous post I described how SSB radio equipment worked and provided an example of a single-band 20m SSB transceiver. In this post I will discuss a multi-band SSB transceiver, an entire homemade amateur station including amplifiers, and conclude with software defined radio (SDR) that you can make in one weekend.

10m and 6m Dual-Band SSB

My second SSB transceiver was dual-band spanning both 6m and 10m wavelengths. I built this radio as part of the ARRL ‘home brew challenge 3’. This followed the same block diagrams as those shown in the previous post except that the two frequency bands of interest spanned one whole octave at 28 MHz and 54 MHz, resulting in additional switching and a wider bandwidth VFO.

Similar fabrication techniques were used, resulting in an old-school appearance.

Schematics and details are found in the full article in March 2013 QST, and design notes here. The interesting thing about this radio is that its VFO, power amplifier, and front-end cover all HF bands up to the VHF band 2m. This radio could quite easily be made into an all-band radio if the filters were built-out.

An Entire Station!

The most impressive home built station I’ve ever seen was by Mark Mandelkern, K5AM.  Mark published details of all this gear in QEX magazine back in the late 1990s and early 2000s, with schematics, block diagrams, and more are available here.

In Mark’s Own Words

“All the gear was newly designed and built from scratch. But I was not about to reinvent the superheterodyne. Each project begins with a thorough study of the handbooks and relevant magazine articles. I glean ideas from all previous builders, to whom many thanks are due. Design means selecting and choosing the best ideas which will help produce the intended results. Individual circuits are described in the handbooks; the real design work is to combine them into a complete functioning unit. Getting a whole station built in a finite interval of time meant using mostly tried-and-true methods, and setting to work without trying to invent a new circuit for each stage.”

There’s More

Others who have made their own multi and single-band SSB transceivers:

And others suggest searching on YouTube for on-air demos of some of these radios or post in the comments section.

Phasing SSB and Software Defined Radio

There are other methods to implement SSB equipment, including direct-conversion using phasing (either digital or analog). In this architecture, an I/Q image rejection mixer is used to mix up (for transmit) or down (for receive) to directly modulate or demodulate SSB signals. The back end after the IQ mixer can be implemented with either op-amps or digitization. This is one of the common architectures for early SSB transmitters and today this is the preferred architecture for entry-level software defined radio (SDR) receivers and transmitters.

Software Defined Radio (SDR)

SDR might be a great option for those of you who are more interested in building a kit or writing code instead of building a scratch-built design.  In many cases the software is already written.  And let’s face it, SDR is the future of radio by pushing what was previously analog circuitry into the digital domain, which trades CPU cycles for reductions in analog circuit complexity.

The Soft Rock SDR transceiver kit.
The Soft Rock SDR transceiver kit.

There are many SDR kits available today, including those by AE9RB, the Picastar, or the Heremes.  You can also buy the commercialized version or can mix and match the exciter, PA, and filter boards.  Recently, an SDR was developed using a teensy. Check out hackrf or hackrfblue for the professional to convert to amateur use with the addition of a good power amplifier and some filters.

The best performing software-defined (or DSP) receivers use a hybrid architecture mixing the best practices of analog design with an SDR back-end (sometimes known as a ‘roofing filter‘).  This provides the high-dynamic range architecture of an analog radio with the flexibility of a software defined radio.  This is why the Elecraft K3 is a top performing radio (it is also available as a kit).

Build It

The only way to get started is to build something. Start small, check out the QRP community, try making a single-conversion receiver, try an entry-level SDR, and finally move up to something with a crystal IF filter. Borrow and scale circuits from books such as these:

Or leverage complete ICs and modules like those from Mini-Circuits. There is nothing like making that first long distance contact on radio gear you created from scratch.


Acknowledgement

My cousin, Juliet Hurley, MBA, MSF, MAC for type editing this post.

Author Bio
Gregory L. Charvat only operates radio equipment he builds from scratch, is the author of Small and Short-Range Radar Systems, co-founder of Hyperfine Research Inc., Butterfly Network Inc. (both of which are 4catalyzer companies), visiting research scientist at Camera Culture Group Massachusetts Institute of Technology Media Lab, editor of the Gregory L. Charvat Series on Practical Approaches to Electrical Engineering, and guest commentator on CNN, CBS, Sky News, and others. He was a technical staff member at MIT Lincoln Laboratory where his work on through-wall radar won best paper at the 2010 MSS Tri-Services Radar Symposium and is an MIT Office of the Provost 2011 research highlight. He has taught short radar courses at MIT where his Build a Small Radar course was the top-ranked MIT professional education course in 2011 and has become widely adopted by other universities, laboratories, and private organizations. Starting at an Early Age, Greg developed numerous radar systems, rail SAR imaging sensors, phased-array radar systems; holds several patents; and has developed many other sensors and radio and audio equipment. He has authored numerous publications and has received press for his work. Greg earned a Ph.D in electrical engineering in 2007, an MSEE in 2003, and a BSEE in 2002 from Michigan State University, and is a senior member of the IEEE where he serves on the steering committee for the 2010, 2013, and 2016 IEEE International Symposium on Phased Array Systems and Technology and chaired the IEEE AP-S Boston Chapter from 2010-2011.

20 thoughts on “Design & Build Part 2: Multi-Band, Phasing SSB, and SDR

  1. The problem many of us have with SDR is that ball and chain called a computer needed to support the radio. Using a mouse and keyboard to control a radio is like using a pair of Vice Grips to steer an automobile, and change gears.

    I’ve built and used SDR radios, so I speak from experience. Put it all in one box and I and others of my ilk will be much happier.

    1. ??? Really ? Your words are contradicting each other. On one you are saying you’ve build SDRs and on other side you are saying you need a mouse and a keyboard?? Ohhh probably you mean to say you’ve used lot of SDR SW with common HW. Just FYI, SDR goes way beyond mouse/keyboard. Surly you can’t use (readily) GNURadio or SDR# in a way you want but if you’d have built an SDR you’d have known that. I can just tell you SDR can be implemented on a chip and if your are competent enough you can build a touch screen GUI to control it. (I don’t mean to be offensive. Just wanted to say I’ve not even used SDR much beyond SDR# with RTLSDR, so definitely you are way ahead of me in terms of using SDR)

    2. i am not a radio amateur, but i assume it could be done in a compact form factor.

      i see the following options:
      1. use a laptop, they make small ones too
      2. dunno about the processing requirements for sdr, but perhaps a RaspberryPiB2 might do the job. add some knobs, a small display and write some sort of scripts to read them and pass the commands to the SDR software. you would probably have to add a mic and headphones/speakers
      3.maybe there are sdr-capable fpga’s?

    3. You don’t need a separate computer to control an SDR.

      You can easily get an embedded microcontroller powerful enough to handle the DSP, frequency control and display all in one box.

    4. This is changing, and the Elecraft KX3 previous mentioned is the leading edge of the new wave in SDR, as I’m sure you’re aware. The big thing is that it is a full function radio in its own right without using the I/Q it has. The one bad thing about existing designs is that they have a lot of latency and certain timing critical applications need to be designed to compensate for it.

  2. “”??? Really ? Your words are contradicting each other. On one you are saying you’ve build SDRs
    “”
    Sorry that isn’t what I said..
    I said I built SDR radios.
    past tense.

    “”
    and on other side you are saying you need a mouse and a keyboard?? Ohhh probably you mean to say you’ve used lot of SDR SW with common HW. Just FYI, SDR goes way beyond mouse/keyboard. Surly you can’t use (readily) GNURadio or SDR# in a way you want but if you’d have built an SDR you’d have known that.
    “”

    I am aware of that however the high end commercial SDR gear still require a computer.
    I suppose you have heard of Flex Radio?
    Not to mention all but two of the links in the above article. They all require an outboard computer.

    “”
    I can just tell you SDR can be implemented on a chip and if your are competent enough you can build a touch screen GUI to control it. (I don’t mean to be offensive. Just wanted to say I’ve not even used SDR much beyond SDR# with RTLSDR, so definitely you are way ahead of me in terms of using SDR)
    “”

    Not meaning to be offencive ether, but I guess you haven’t much experience in the day to day use of a transceiver be it commercial or ham, they are not very ergonomic.

    While you can implement SDR in a chip (not new at all been going on for at least a dozen nears now) that represents a series of compromises that the chip designer makes, and is not always the best route to high performance equipment.

    SDR has a ways to go before the performance of non-SDR gear is equaled and surpassed.
    Until then…………

    Take Care
    AF6LJ

    1. I think the Elecraft KX3 ( http://www.elecraft.com ) is a good example of a well thought out standalone SDR with performance WELL past all analog radios, by almost every measure. I realize this thread is about DIY, but I use that example of a good standalone architecture. I agree what is lacking in availability is a generic, standardized IF, open source digital back-end, optimized for DIY builders. So much of the existing stuff is still of the low or zero IF variety simply because it is easier than tackling demodulation and filtering in the digital domain. Granted, the Elecraft is also the low IF variety but I think we will see the IFs coming up in frequency, BW and general capabilities escalating toward the likes of Flex over the next few years.
      Regards,
      Mike WO1U

  3. The closest I have come to Amateur Radio is owning a CB radio many decades ago (27 MHz). I have worked a lot with modulation in the communications field, which was all sideband modulation and many stages of it.

    But just as a plain tech, I have to take my hat off to Mark Mandelkern. Some of his gear (that is still working fine) was built by him as far back as 1951. That’s 64 years and a very strong statement to his ability.

      1. These days CB is a non contender in getting started in radio, especially since a technician license is so easy to get and doesn’t require breaking the FCC regs to use different modes and work DX.

  4. First off, thanks very much for bringing RF design to Hackaday!

    That list of reading is decent, but keep in mind that Solid State Design for the Radio Amateur is long out of print and has been “replaced” by Experimental Methods in RF Design.

    http://www.arrl.org/shop/Experimental-Methods-in-RF-Design

    A lot of us ham radio/QRP geeks consider EMRFD to be our “bible”. It is the first book that I recommend to anyone looking at getting into RF design and experimentation. A close second is the ARRL Handbook, which is an excellent RF reference guide, even if you are not a radio amateur.

    73,
    Jason NT7S

      1. Yes it does, enough to get you in the ballpark.
        The supplemental CD that comes with the book has articles that are footnoted, programs and additional data for projects outlined out in the book.
        It is worth the $49.00US….

        1. Any good computer programs to estimate transistor input/output stage impedances? That would be fantastic, although it is pretty easy to do with a pocket calculator. Its alot like the filter calculator that comes with the handbook, so nice to just automatically get the values and iterate a design.

          1. I know what you mean, I haven’t seen the need to get a computer program for that.
            The calculations get you pointed in the right direction and you are good to do.

            This book is good for those who are already past the basics. it is a good follow on to a whole bunch of texts. While there are plenty of example circuits that can be made to work with little trouble the book assumes the reader has some (not very much) RF background.

  5. I have tinkered with SDR Radio a bit. The bug bit me while over in Germany back in 2013 while visiting a good friend of mine (DG1MHC). He recently bought a HackRF box, and I’m going to go the same route. I still play with my Kenwood TS-570 (HF) and my Wouxun handhelds. One thing I am certain, you can learn a lot about RF from a HAM, Engineer, Technician, and…teacher. I’ve shown the neighborhood kids the fun of the hobby, and some of them wanted to take their test in March at the Hamfest here in Charleston…all thanks to their “tech guru.” I just wish there would be a stronger hacker movement here in my neck of the woods to garner more people to embrace the change and make things. ;) SDR will still be the grandchild of Mr. Heterodyne and Mrs. Crystal Radio…we need to nurture that child and make it our future. 73’s – KC8KVA

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