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Thursday, February 4, 2016

A Probable First: First Ever Radio Contact Using Unijunction Transistor as the Transmitter

AA1TJ writes:

I spent most of a week working to raise the RF output power from my unijunction transmitter to nearly 1mW. I was rewarded this evening with two contacts.

Jim/W1PID exchanged (599/449) signal reports with me from Sanbornton, NH (112km) at 2210z!

Dave/K1SWL did the same (589/229) from Newport, NH (95km) some four minutes later!

I should think these were the first-ever radio contacts made using a unijunction transistor as the transmitter.

FYI: my receiver was comprised of a single 1N34a germanium diode mixer followed by a single 2N35 germanium transistor audio amplifier. Great signals on this end.

Wikipedia on Unijunction Transistors: https://en.wikipedia.org/wiki/Unijunction_transistor


  1. Now you know how Marconi felt!
    Great story.

  2. This comment has been removed by the author.

  3. K1SWL reports that my (95km distant) signal climbed out of the noise to peak at S-9 for a period lasting several seconds, after which it fell back into the noise. W1PID (112km) witnessed the same event, but with a less dramatic peak signal level. I'm admit to knowing little-to-nothing about 80m propagation. Meteor trail reflection? Hovering alien Mothership? ...although I allow there may be a more mundane explanation for this dramatic, sudden path enhancement. Ideas?

    1. Well,
      I know not much about 80m propagation either, but it seems like it must have been quite a localized event, that caused the peak? Since 17km away the effect was a lot less strong..?
      Theoretically seen, aircraft doe produce reflections at such low frequencies. If you look at Chain Home, ran originally on 6 MHz...
      Just a suggestion...
      Never heard of any aircraft scatter at 80 meters! But, it is possible at the right angle/altitude etc it worked as a reflector...

  4. Oops, the above post was by AA1TJ

    1. Ow by the way, what type of UJT are you using? And got any idea on the waveform?
      Yes a lot of questions, but this caught my fascination!

  5. Damn it, you pulled it off before me!
    I never got the output of the UJT with 160m crystal without a lot of noise...
    Gave up on it a long time ago, after you sent a PCT :-) Didn't have my ticket back than, the worst part I've got it over 2 years now... And didn't make a single QSO yet. Besides messing around point-point with B-K oscillators on 70 and 13cm. A 1-triode, 2-transistor 13cm band RX running on 9V! Or pentodes used as klystrons, very easy to do.

    But how did you do it?
    You got any schematic?
    By coincidence I was looking at the UJT again, thinking about how to make a electronic PCT-equivalent.
    But quickly dropped it for the an Enhacement Mode MOSFET, with the Gate made very leaky with resistors.


  6. Hello Thomas,

    Tnx OM. It's wonderful to hear from you! I think we have much to discuss ;-) I'll send you an email (provided you have the same Gmail account).

    Mike, AA1TJ

    1. Yes I still have my Gmail adress, linked to this account now. Haven't used it in ages tough.

      This is the account linked to my email-adres. Not really running anything solid-state involved right now, neither HF. Just the triodes running as a B-K oscillator, another negative resistance device :-) UHF/microwave transmitter consisting of a triode, 4 RFCs and some form of antenna. Don't get much simpler ;)

      Now gotta go,
      Looking forward to hear from your succes with the UJT!
      Thomas, ON4CPT

  7. I was pleased to have added five more unijunction QSOs to my logbook last evening. My best DX thus far (AA1MY/Maine) is 161km.

    Mike, AA1TJ


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