My First-Ever QSO -- 50 Years After Passing Ham Test

Discussion in 'Ham Radio Discussions' started by G3EDM, Aug 27, 2021.

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  1. G3EDM

    G3EDM Ham Member QRZ Page

    Good morning!

    Calling CQ, somewhere on 40m.

    73 de Martin, G3EDM
  2. G3EDM

    G3EDM Ham Member QRZ Page

    The noise level is much better than yesterday, very quiet. Hearing a K9 callsign engaged in a QSO not far from my 40m calling frequency.

    Another cup of coffee, then resuming calling CQ.

    73 de Martin, G3EDM
  3. G3EDM

    G3EDM Ham Member QRZ Page

    Traffic heard here this morning near my calling frequency is heavily dominated by east-central Europe. Bulgaria, Ukraine, Belarus, Russia.... That is not an unusual pattern here, it's just even more pronounced today. I assume it's a function of the skip distance but also the fact that they are a couple of time zones ahead, so they are awake and operating in early daylight hours.

    Many of them are calling CQ DX so I am not trying to answer them. Just slotting my little signal somewhere in the general neighbourhood as I continue to call CQ.

    Edited to add: Some of them are coming in so strong that I can hear them even with the T/R switch in TRANSMIT position (and before I turn down the AF gain prior to keying CQ). In that configuration, the antenna is disconnected from the receiver, so the signal is reaching right into my shack and being picked up by the open-chassis wiring in the RF stage of the receiver.

    Haven't heard any U.S. traffic for more than an hour.

    73 de Martin, G3EDM
    Last edited: Sep 14, 2021
  4. G3EDM

    G3EDM Ham Member QRZ Page

    Getting deafening breakthrough of a shortwave broadcaster, sounds like Russian.

    It is the same station popping up at approximately 15 kHz intervals throughout the 40m CW segment, at approximately 7010, 7025, 7040, 7055 and so forth.

    That pattern suggest, to me, bad rejection in my receiver. I'm a bit curious about the harmonic repetition though. It must be beating with something, but what? This is very different from when I got BC breakthrough on my ARRL receiver. In that case, it was usually blanketing the entire band, rather than repeating on the dial at regular intervals.

    In general, it would be interesting to hear from Zedders whether BC breakthrough is still a problem on 40m. It was a big issue in Ye Olden Days but I was rather assuming that (a) there is less SW BC activity nowadays, and (b) modern receivers have better rejection characteristics.

    Today's SW BC activity is not preventing me from hearing ham traffic as long as I stay away from those 15kHz-spaced slots.

    73 de Martin, G3EDM
  5. W9BRD

    W9BRD Ham Member QRZ Page

    I did exactly that with my Drake R-4A receiver. The Drake 4-Line MUTE line is "normally closed", but The W9BRD System assumes "ground to mute." Two relays, a driven-by-heater-ac added internal power supply, a transistor for control and a few other components, and my R-4A is "ground to mute" and provides transmitted-signal monitoring with no added pops or clicks. Still figuring out how to add a MONITOR LEVEL control...

    And then there's how every tube transmitter I use (aside from one-tube-oscillator jobs) is designed or modified to cathode-key driver and final, another aspect of The W9BRD System that involves the use of separate high-voltage power MOSFETs for shaped driver-final keying such that the keying characteristics of all transmitters used with the System are essentially the same.
    G3EDM likes this.
  6. W9BRD

    W9BRD Ham Member QRZ Page

    That sounds like 3rd-order intermodulation distortion overload between two closely spaced 41 m broadcasters. If you can tune the RF-amp grid to somewhere down below 40 m, that might help somewhat. Resistive input attenuation could also help.

    I have a sleeve of 1AD4s coming, and sometime soon I want to experiment with the circuit you're using. We should be able to do away with the TRF stage, for starters; then I want to go high-C with the detector tank... :)
    G3EDM likes this.
  7. W9BRD

    W9BRD Ham Member QRZ Page

    At the moment, using G4DYA's KiwiSDR at Staffordshire, I'm seeing multiple strong signals at 41 m, but in particular one at 7115 and an immense signal at 7325 -- a 10-kHz spacing. It even possible that 49-m broadcasters are in play.
    G3EDM likes this.
  8. W9BRD

    W9BRD Ham Member QRZ Page

    I realize on studying the receiver schematic more closely that the set's built-in method of RF GAIN control makes the RF stage easier to overload as gain is reduced. This is so because the 1AD4 is a "sharp cutoff" tube; that equates to meaning that if we want the set to better handle strong signals without generating fake signals through intermodulation distortion (IMD), we should let the RF tube run at full gain -- normal class A bias -- and control signal input to the set with a low-value pot in the antenna line to the first stage.

    A "remote-cutoff" tube in the RF amplifier position would be less prone to fake-signal creation through IMD as its grid bias is increased toward cutoff. But I submit that the receiver doesn't need a common-cathode, RF-amp gain stage at all and would better handle strong signals without it. More as we go.
    Last edited: Sep 14, 2021
    G3EDM likes this.
  9. G3EDM

    G3EDM Ham Member QRZ Page

    Ahhh. I had not thought about that. Makes sense.

    Yes, I can reduce the issue somewhat by de-tuning the RF amp downwards (which, as you know, is tuneable). There is not much travel on that side of the capacitor: for the bottom of 40m I peak it at around 15 on the vernier dial, so the plates are fairly fully meshed already. The trouble of course with de-peaking is it reduces sensitivity overall, but it can be a useful tradeoff.

    You must be an incorrigible experimenter to want to build something like this one....

    The history of that set is that I originally built a very conventional one-tube regen using the 1AD4, with the exception that I did add the "regeneration throttle" that is often missing from these designs. I started a thread about it over on eHam and before you knew it, G3RZP and KB1GMX were essentially "re-building" it for me at a distance, making numerous suggestions, most of which led to noticeable improvements in the set.

    IIRC the biggest improvement came from adding the RF stage, which made a noticeable difference in the handling of strong signals and the stability of the set in general. Also, if you know G3RZP you will know that he is (commendably!) a stickler for avoiding stray emissions and he did not like the idea of my regenerative radios polluting the airwaves with their oscillators, so he insisted on adding that stage if only to isolate the oscillator from the antenna....

    So I am curious as to why you want do do away with it....

    I cannot remember all of the changes they suggested, and unfortunately cannot find that old eHam thread. But nearly all the changes are reflected in that circuit diagram I posted, with the exception of the AF gain circuit, which I have also posted separately in this thread.

    But these are a couple of the changes I remember:
    • Using really large plate loads on the detector and the first AF (60H!).
    • Adding battery-driven grid bias to the RF stage and 1st AF.
    One change that I made was adding that pot to vary the B+ on the detector. That voltage value is critical, and its optimal value varies depending on other stuff going on, such as the amount of regeneration.

    The set actually has seven tubes: there's a two-tube audio filter, and a two-tube push-pull second AF. But those are not functionally part of the core of this set.

    Concerning the overall design of regenerative receivers I have been influenced in part by more modern designs by N1TEV (Charles Kitchin) published in various places and some of which can be found on the Web. The "regeneration throttle" is one of them. He also has interesting things to say about the layout and spacing of the components of a regenerative detector. IIRC all of his designs are solid-state but the principles he discusses apply equally to hollow-state regens.

    I'll be fascinated to see what you make of the 1AD4 option for homebrewing receivers. I had a lot of fun with it, and the result is not unimpressive.

    Back to calling CQ.

    73 de Martin, G3EDM
  10. G3EDM

    G3EDM Ham Member QRZ Page

    I'm not sure that any subminiature tubes have cathodes, I think they may all be directly heated. Having to rely on directly heated tubes was a handicap in the design of this set, I remember that much. It was only six years ago but a lot of water has flowed under the bridge, including my move to the UK a bit more than three years ago....

    73 de Martin, G3EDM

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