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What do you do once you are already a skilled radio designer and restorer? Well, if you are Greg Charvat, you decide to build a shortwave radio using a single type of transistor as an active element. Normally, one would use number of different transistors, each designed to handle different amounts of power and amplifying bandwidth. Limiting yourself to a single type may seem like a mental exercise today (pun intended), but was apparently much more common back when transistors weren’t easy to come by, so Greg isn’t completely off his rocker. Also, by only using one kind of part, it should make repairs much easier.

Designing a radio like this is a little bit complicated, but not nearly as much as it might sound. The trick is to divide the radio function into manageable pieces, which can then be designed and tested individually. You will notice that Greg’s radio (pictured above) is made up of a bunch of small prototyping boards. Each board contains a single circuit with a specific function, and physically separating them makes it much easier to test the parts, as well as swap out the ones that might be malfunctioning. It’s also a neat design aesthetic, because it very closely resembles the way you would draw an electrical schematic to represent the circuit.

If you are interested in building a radio, I would strongly recommend giving it a go. Start with a kit, though, and pick one that explains the design of each stage so that you can learn how it works. It will definitely be an interesting experience, and who knows, it could be the start of a new passion! If you have a favorite kit or other guide to recommend, chime in on the comments.


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Comments

  1. rallen says:

    I used to work on a RF Communications Monitor (IFR 1200/S/Super/SS) and we used to joke that the guts were designed using 1970′s technology. It was made in RF-sealed modules so the bench tech’s could pluck-n-chuck and get them back to their owners quickly. That design also made them incredibly versatile. They could do some amazing things that would compete with the company’s high-end equipment, if you knew what to do.

    1. Matt Mets says:

      Ha, that actually sounds like a really good example for the whole design for repair/modification drive :-)

  2. Martinelli says:

    It looks like rocket science to me. I think I would never be able to do that and this way I admire you guys.

  3. kd6fvi says:

    Had a design contest for a transceiver using 2N222 transistors only. http://www.norcalqrp.org.

    1. Gregory Charvat says:

      Yes, the 2N2222 design contest was one of the things that i modeled this project off of.

      For those who are not familiar, the winner of this contest made an amazing two-way (TX and RX) radio out of only 2N2222 NPN transistors.

      I learned a few things in researching the results of your design contest. One of which was to use Norton type RF amplifier topology when using general purpose transistors at RF frequencies so as to prevent oscillation and achieve best possible noise figure.

      My radio is much less sophisticated than the winner of the 2N2222 design challenge. I was really impressed with your results :)

      Could you post a link to the winner’s radio page?

  4. Gregory Charvat says:

    Hi everyone,

    After reading all of your comments i went ahead and scanned all of my notes on this radio, here is the schematic:

    http://web.mit.edu/gr20603/www/website%20pdfs/trans_radio_schematic.pdf

    Here is the web page that i wrote up for it:
    http://www.mit.edu/~gr20603/Dr.%20Gregory%20L.%20Charvat%20Projects/Transistor%20Radio%20From%20Scratch.html

    Some additional photos:
    http://www.mit.edu/~gr20603/Dr.%20Gregory%20L.%20Charvat%20Projects/transistor%20radio%20photos.html

    If you make it in a modular fashion as Matt has described then i think you will have a good chance at success. It is just one IF amplifier, mixer, oscillator, or filter at a time.

    You can do this, it is not rocket science but it is somewhat challenging. There are some great kits out there for you that take the tedious design work out and allow you to learn. I agree with Matt that these are a good place to start.

    I wish you the best of luck!

    Greg

    1. PRCalDude says:

      Do you have any radio kits you recommend?

  5. Chris W says:

    Pretty impressive, but he actually used two types. Even the early radios had multiple transistor types. It would be even more challenging to use only one value of resistor or capacitor.
    It looks a lot like my two identical Heathkit TVs each having 21 PCBs, 13 of them plug in. Almost all the transistors and ICs are socketed. Very easy to repair!

  6. craig says:

    Martinelli,
    If you can buy one cheap, you might like the Radio Ace 1 tube radio. It is not a ‘kit’ in the sense, it has 2 different coils to choose from, one tube, 3 binding posts for antenna and 1 for ground. I just love the mellow golden sound of AM tube radio. Even though I amplify it through a modern stereo amp. Even Dennis Miller talk radio sounds good through vacuum tube AM. I love the look of the redwood cabinet also. Check it out.

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