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

    The transmitter saga is taking an unexpected turn.

    After a half-dozen modifications to my circuit, resulting in some major improvements, I have decided that in the longer term the transmitter is still not good enough.

    I had a lot of fun scoring QSOs but it fairly quickly became obvious that the signal was flawed. When the transmitter was modified, the signal improved such that it sounds very good on the air. But doing so also resulted in reduced drive to the Power Amplifier tube, considerably reducing the transmitter's usable power.

    For a short while I will continue operating with what I have, using only a handful of very robust vintage crystals that can tolerate being driven hard.

    However, within the next few weeks I will begin an effort completely to rewire the oscillator circuit, replacing the Pierce oscillator with an ECO (Electron-Coupled Oscillator).

    This will provide the following advantages:
    • Oscillator stability, which is why this whole modification saga began.
    • Increased drive to the PA, pushing it (we assume) into Class C operation and maximum power for this little transmitter.
    • Greater flexibility with easy connection to the future VFO.
    It can be done without making any external modifications to the appearance of the transmitter. If the internal modification is successful, it makes the transmitter much more useful, within, of course, the limitations of operating QRP.

    (The above is a non-technical summary of today's transmitter developments. For the full, gory details in their full technical glory see the much fuller posts in the Homebrew forum. The thread is called "Oscillator/PA Cathode Keying, 'Spotting' Your Frequency, and Chirp". The title of the thread is now off-topic but it does have the advantage that almost the entire G3EDM transmitter saga is confined to one thread, in full technical detail.)

    73 de Martin, G3EDM
     
    G0CIQ likes this.
  2. G3EDM

    G3EDM Ham Member QRZ Page

    The components for the various improvement projects (transmitter, receiver, T/R switch) are trickling in. Part of today's haul:

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    73 de Martin, G3EDM
     
    G0CIQ likes this.
  3. G0CIQ

    G0CIQ Ham Member QRZ Page

    Hi Martin,
    I've had a look through the videos, the dial frequency of the first video was 7005.24 and that of the third was 7031.34; I couldn't see the others.
    I don't know how accurate this is but as an indication the transmissions on 20m resulted in RBN spotted frequencies of 14059.5 (VE2WU) and 14059.6 (3V8SS) for a dial frequency of 14060.0 so I guess it's not that far out!
    Hoping to check the accuracy of the 817 as part of installing the temperature compensated oscillator at some point.
    73,
    Simon.
     
    G3EDM likes this.
  4. G3EDM

    G3EDM Ham Member QRZ Page

    Thanks Simon. When we did those tests, RBN spotted my signal:
    • On the first crystal as between 7005.3 and 7005.5 (this is a "vintage" FT-243). You had one of the transmissions as 7005.24, which is extremely close to RBN.
    • On the second crystal as between 7031.1 and 7031.4 (this is a modern crystal stuffed into an FT-243 case). You had one of the transmissions at 7031.4, which matches at least one of the RBN readings.
    The tests that we did together naturally "pull" the frequency of a crystal up or down because I was constantly changing the oscillator drive level as well as the plate supply voltage (which also, obviously, alters the drive level). There were eight configurations of drive level and crystal that were tested. The first four videos were at a plate voltage of about 230 volts, the second four were at about 140V (after inserting a voltage regulator tube instead of a power resistor). Within those groups of four, I tested two different crystals and two different levels (high and low) for the oscillator's drive control (a potentiometer in the cathode circuit).

    73 de Martin, G3EDM
     
    G0CIQ likes this.
  5. WQ2H

    WQ2H QRZ Lifetime Member #214 Platinum Subscriber Life Member QRZ Page

    Martin,

    Just came across this. Congrats ! And no more "dithering" ! :)

    Good luck, and best with future QSO's.

    73
    Jim, WQ2H
     
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  6. G3EDM

    G3EDM Ham Member QRZ Page

    Today has been spent Taming The Beast.

    My second receiver is of my own design, albeit totally copied from existing generic designs for good regenerative radios. It uses "subminiature" tubes which are about the size and shape of a pencil eraser. For the past couple of weeks it has been "in the clinic" but today I got it working again, and its performance is way better than before. Long story, but basically I made a mistake when wiring the detector four years ago and inadvertently introduced a vicious feedback loop.

    The receiver now really "sings" albeit with the well-known drawbacks of a regenerative circuit. Furthermore, I also managed to get the CW audio filter working. I built this into the radio, based on ARRL's "Audiofil" designs and it can be very effective under the right conditions.

    "Taming the Beast" also includes making it take up less space in my small shack. It was originally built on a plank of wood, about 25 inches (64 cm) wide and 12 inches (30 cm) deep. It basically took up about two-thirds of the tiny shack desk. Today I sawed it in half (!) and stacked the two halves on top of each other to make a "vertical" design. I also sawed off the "power supply" which is a massive bank of batteries supplying the three different voltages required. It originally took up a strip 4 inches (10 cm) deep along the entire back of the radio. The "power supply" will go on a shelf in the closet and be wired to the radio.

    Now I just have to wire all the radio's stages back together again. It is a "modular" design and when I sawed the plank in half, I had to remove or at least disconnect most of the inter-module wiring.

    The new layout is only 13 inches (33 cm) wide and 8 inches (20 cm) deep! It's rather taller of course, and the tuning knob is a bit high up for my taste, but those are minor issues given how much space has been saved. (The RF deck has to go on top otherwise the controls at the back of that open top deck could not be reached.)

    [​IMG]

    Sometime in the next couple of days I will start a thread over in Homebrew about this set, once it has all been finally put back together again.

    73 de Martin, G3EDM
     
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  7. G3EDM

    G3EDM Ham Member QRZ Page

    I used to look at pictures of other hams' shacks and think: How can they possibly amass so much gear?

    Well, "scope creep" is alive and well at G3EDM:

    [​IMG]

    73 de Martin, G3EDM
     
    G0CIQ, W0PV, AD5HR and 2 others like this.
  8. G3EDM

    G3EDM Ham Member QRZ Page

    Today, my regenerative receiver built with subminiature tubes is finally back in operation and performing quite well. (The CW audio filter is broken again, will work on that when I have time.) The set firstly needed repairs, and secondly was rebuilt in a "vertical" form factor with the power supply moved outboard. It is no longer "The Beast" and now a relatively manageable size.

    For those interested in the full technical story (and photos) of the receiver, please visit my new thread called "High Performance Regenerative Receivers" in the "Homebrew and Kit Projects" forum.

    The transmitter is in a transitional state prior to modifications, but I have patched it up such that it can be used on the air with a selection of "known good" crystals.

    What I really want to do now is operate on the air with what I have, flawed though it may be. After two weeks of being QRT I have lost a dangerous amount in operating skills and CW -- I was really only just getting started in earnest when all these technical issues knocked me off course for a while.

    [​IMG]

    A couple of days ago the new OB2 regulator tubes for the transmitter arrived. These will be wired in series to stabilize the plate voltage on the transmitter's oscillator at 216 volts. This is probably temporary, until I have the components, and the time, to make more fundamental modifications to the oscillator. (These involve changing it from a Pierce triode circuit, to an Electron Coupled pentode circuit, thereby -- we hope -- solving a number of fundamental problems with the original transmitter.)

    [​IMG]

    73 de Martin, G3EDM
     
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  9. G3EDM

    G3EDM Ham Member QRZ Page

    So this is what I was up to during the past weekend: literally sawing my receiver in half and repackaging it for my tiny shack.

    That only took a few hours. Not shown: the painstaking work of re-wiring the set after it had been completely dismantled and then rebuilt in a completely different shape.

    The "workshop" is out dining-room table....

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    73 de Martin, G3EDM
     
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  10. WD5GWY

    WD5GWY Premium Subscriber QRZ Page

    That so neat!
    I have enjoyed following your progress on this project.
    James
    WD5GWY
     
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