ad: w5yi

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

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

  1. G3EDM

    G3EDM Ham Member QRZ Page

    At secondary school (high school) my Elmer, Mr. Andrews, shared his station with everyone who used the Electronics Lab. The Lab was an after-lessons optional activity and for a couple of years I basically lived there.

    Mr. Andrews (G3PNV, still listed on the Zed) also had a small private office for his teaching duties, next door to The Lab. I only got to go in there a few times but pride of place was taken by his R1155.

    73 de Martin, G3EDM
    N2EY likes this.
  2. G3EDM

    G3EDM Ham Member QRZ Page

    Just drawing attention to my post #807. It raises the idea of using our damp, leaky and un-insulated garden shed as a ham shack and homebrewing workshop. The idea came to me yesterday when I was mowing the lawn.

    Ideas welcome, especially from UK or nearby European readers who share roughly the same weather climate and are in fact themselves using a traditional Garden Shed as their ham shack.

    The context is: We are renting our house and that situation is likely to continue into the medium-term future. So we cannot make major alterations such as adding a new building.

    After a night's sleep I am starting to think that a halfway solution might make sense. Keep the operating station inside the house, despite the disadvantages (lack of space and need to vacate it whenever we have guests, since it is in the spare bedroom). But use the Garden Shed as my workshop for homebrewing, at the very least for the metal-bashing and other stuff that is noisy and to some extent dirty, spewing metal filings and so forth.

    I could buy a cheap drill press, like I did in America, put it in the Garden Shed (if the floor can bear it!) and not worry about damp damaging it because if it eventually dies because of rust/corrosion, it is still better than nothing and much cheaper than renting workshop space elsewhere. I could also keep a selection of hand tools in there, once again deciding not to worry too much about corrosion. Sensitive gear such as test equipment could be kept in the house and brought out to the Garden Shed on as-needed basis. Or perhaps I could build a weather-insulated cupboard inside the Garden Shed, to hold fragile equipment.

    The very limited "homebrewing" I've been doing in the past few weeks has alternated between the shack (spare bedroom), the tiny kitchen (no table, using the counter) and the small conservatory we use as a dining room. It takes quite a while to set up each time, and my wife is greeted by a bomb-site when she goes into those rooms.

    I don't think it's fair to the rest of the family when one's hobby takes over the house in this way. We all have our hobbies (well, actually, some people don't have hobbies, sadly) and that's great, but "the ham is balanced" and all that.

    Edited to add: I expect that some old-timers may chime in with, "I built my transmitter on my kitchen table" and so forth. But those are often tales of Ancient Days when we were younger. In my current life stage (my wife and I are in our mid-60s) a certain amount of tidiness and predictability in Life tend to be more important than when we were younger.


    73 de Martin, G3EDM
    Last edited: Sep 20, 2021
    G0CIQ likes this.
  3. G3EDM

    G3EDM Ham Member QRZ Page

    This is all great stuff. In the next few weeks I do hope to retrieve some things from storage including the VTVM and an RF signal generator. But I could measure the drive into the PA with what I already have in the house. IIRC, lifting the grounded end of the grid resistor just involves un-screwing one of the tube-socket's mounting screws and lifting the grounding lug. I have all of the components and gear that you mention.

    Ditto with the VR tube, an easy modification to make, I could just put a 1/2W 10-ohm resistor in there. I could even bridge it with a jumper, and lift the jumper when I want to make measurements.

    While we are on the subject of drive into the PA, let me ask one of my usual trademarked dumb questions. What does the resulting measurement signify? What are the consequences of too-low drive or too-high drive?

    I'm naïvely thinking that too-high drive could be one of the factors in "pulling" the oscillator when the PA is keyed, but maybe that is more the case with too-low drive??

    73 de Martin, G3EDM
  4. G3EDM

    G3EDM Ham Member QRZ Page

    How close to the bottom of the 40m band can one safely operate CW?

    Reading about this, the bandwidth depends in part on how fast you are sending.

    But it seems like, if your CF is for example 7001.0 kHz, then you are safe, the lower sideband should not spill over into forbidden space or at least the skirts should be good enough that the dB-level is much attenuated at the edge, essentially equivalent to a zero-power signal.

    Asking because I've bought a crystal that is vintage FT-243 and is marked as 7000 kHz. But so far, every single crystal in my collection has oscillated slightly higher than the marked frequency.... So I took a calculated gamble.

    (If it turns out that the 7000 kHz crystal is too close to the band edge, I will make use of it only as a frequency marker for calibrating my receivers.)

    73 de Martin, G3EDM
  5. W9BRD

    W9BRD Ham Member QRZ Page

    Too-low drive to a self-biased class C amplifier -- which what your Boosted Pierce has -- causes the tube to draw too much plate current because of insufficiently high negative grid bias. The tube plate may overheat. (Think of the limiting case: No drive at all. You'd probably see your 5763's plate glow red -- very bad, potentially permanently damaging the tube. In many simple class C amplifiers, one of which your circuit uses, base don the 5763, the negative bias voltage needed for good class C operation is produced by rectification of the driving signal in the diode formed by the tube control grid and cathode. The resulting dc pulses charge the associated circuit capacitances to set a direct voltage level that serves as bias. Insufficient to no drive = low to no bias. With low to no bias, the keyed tube draw dangerously high plate current.

    Too-high drive can cause the plate and screen to draw too much current, but tube efficiency drops first, meaning that power output diminishes with increasing drive. (If the oscillator tube was capable of overdrive on 40 m -- which it likely is not, although your transmitter's supply voltage is considerably higher than that reported by Mix -- and you could smoothly vary the driving signal produced by the oscillator tube, you'd see that RF output passed through a peak you adjusted the driving signal from not enough to too much.)

    Overdrive to the crystal within the 6C4/6AB4 circuit alone is far and away the greater reason for frequency instability in a Boosted Pierce. A power Pierce oscillator -- one that's supplied at a relatively high voltage to make it produce power instead of just a controlling voltage -- is especially potentially dangerous to its crystals.

    But insufficient isolation of the crystal and crystal oscillator circuit is another characteristic of the Boosted Pierce, meaning that goings-on in the final amplifier stage, including output power fed back to its control grid as a result of the absence of neutralization. In my page on the circuit, did you notice where I describe that quite commonly in Boosted Pierce circuits, the power amplifier tube may "take over" as an inefficient crystal oscillator if we pull the oscillator tube out of its socket? There's no better proof of how bad a design the Boosted Pierce is, how nonexistent is isolation between its oscillator and amplifier stages, than that.

    The Boosted Pierce caught on because it's better than a single-tube-crystal-oscillator transmitter in some ways. That's where "better" and "good enough" end for the BP.

    We've been helping you get the most out of Mix's circuit by working through optimization of some values and using a more crystal-friendly oscillator tube. And you've found some vintage components that misbehaved as a result of aging. But with all respect due to your hobbyist choice of the circuit long ago, the Boosted Pierce was a bad design in 1938 and an even worse design in 1968 (because standards for frequency stability were higher; because commonly available crystals had become intolerant of its excessive crystal stress; and because effective means of neutralizing such tubes as the 5763 had long since been available, allow us to better-engineer transmitters with confidence). In 1968, the Boosted Pierce was an example of ham-radio thought leaders oversimplifying technical requirements to get more and younger hams "into the tent" for less complexity of effort at lower cost -- and ultimately disserving them as a result.
    Last edited: Sep 20, 2021
    G3EDM likes this.
  6. W9BRD

    W9BRD Ham Member QRZ Page

    With your circuit and your crystals, I wouldn't go closer than 7005, and would think very strongly about building or acquiring a "crystal calibrator" to give you a receiver-and-transmitter-independent marker at 7000 kHz. A non-overloadable, unambiguous means of comparing your transmitter's output frequency to the frequency of such a marker in real time is also a necessity.

    In the absence of the "I'm in the band" assurance provided by such a setup, use crystals well within the band. Do NOT use a crystal marked "7000" and hope that it's "oscillating high" as a result of other experience. Just don't.
    Last edited: Sep 20, 2021
    G3EDM likes this.
  7. G3EDM

    G3EDM Ham Member QRZ Page

    Very good to know, thanks. I was thinking of building a small calibrator anyway. I remember building one as a 13-year-old to plug into the accessory socket of my HR-10B. Heathkit marketed a kit calibrator, but I built my own instead, based on a 100kHz crystal.

    Sorry I may have been a bit misleading in my post. I did not intend to just go on the air with that "7000 kHz" crystal and "hope" it was higher. I would have done some tests with the unkeyed TX oscillator and "spotted" the crystal along with others whose frequency I already know. But I take your point that it is not worth the risk. Well, nothing is worth the risk: one does not go on the air "hoping" to be within-band, one does it knowing for sure, in advance!

    Edited to add: I already have a crystal that RBN spots at either 7004.9 or exactly 7005.0 and that's the lowest I will go, based on what you said. It happens to be a really "good crystal" which is why I'm often to be found operating there.

    73 de Martin, G3EDM
    W9BRD likes this.
  8. G3EDM

    G3EDM Ham Member QRZ Page

    OK good. I will definitely go ahead and measure the voltage drop in the way you describe. I'll probably wait until after trying out the VR tube, then test the PA drive level in whatever the relatively "final" TX configuration turns out to be. Here's hoping that the drive level is not too far out of whack; this round of modifications is beginning to be exhausting!

    73 de Martin, G3EDM
  9. SM0AOM

    SM0AOM Ham Member QRZ Page

    Somewhat depending on the crystal cut and processing, the frequency generally drifts downwards when the crystal heats up. For "realistic" amounts of heat, this is usually confined to about 100 or 200 Hz which still is an objectionable amount of "chirp" or "yoop".

    How close to the band edge that one can operate, is a subject open to debate among amateurs, as is how the occupied bandwidth for an A1A emission should be calculated.

    The ITU Radio Regulations use a model for the keying spectrum which comes out of an approximation of the Fourier spectrum of the envelope function, assuming proper shaping, of
    occupied bandwidth B = 5*keying rate in Bauds. 10 Baud corresponds to 10 WPM, and the average rate for a Novice can be estimated as 10 to 15 WPM range. So a reasonable value for the occupied bandwidth could be 75 Hz, and all radio users are formally required to stay at least half of the occupied bandwidth away from the band edges. 40 or 50 Hz should be sufficient in your case.

    In the "old days", Government monitors sometimes hanged out around the bottom edges of the
    amateur bands, waiting for some unwary amateur to drift outside the band. A friend of mine,
    an "OOT", was a Novice during the early-60s, and had a crystal marked 7002 kc.

    After a considerable amount of 40 m operations, a brown official envelope one day showed up in his mail containing a citation for operating on 6999.937 kc, and demanding an explanation.

    He wrote back stating that his crystal was marked with an in-band frequency, and he had marked
    the lower band-edge on his ancient HRO using this value. In return, he got a somewhat more nicely formulated letter, explaining that a crystal had both series and parallel resonances, and also that marked frequencies should not be relied on, but instead an independent standard such as a crystal calibrator should be used. Finally a schematic of an oscillator circuit which would provide a frequency safely in the band when properly adjusted was included.

    Today, it is highly unlikely that any Government monitor would take the time to monitor a band-edge, and even less likely that they will write a letter back with advice and a schematic.

    I would also say that the BP transmitter design is somewhat of a "dead-end", and definitely should be avoided for higher power operation. Amateur band crystals are so expensive today that they deserve a better fate than being overloaded.

    A good VFO is a project that should not be undertaken lightly, but as long as some planning and precautions are made, the results can be quite rewarding. In my day, I have built and used most of the "common" VFO designs; Hartley, Colpitts and Clapp, but the Franklin and Vackar oscillators are among of the best, as they use very loose coupling to the tuned circuit, and RF grounded cathodes. This makes the "bane" of vacuum-tube VFO:s, modulation hum from the AC heater, much less of a problem.

    Part of the charm of "vintage gear operating" is also a certain amount of hum, chirp, drift, and to a smaller extent, clicks. Any reasonably designed Novice rig should have better keying shaping than the more atrocious "plastic radios" around today.

    Last edited: Sep 20, 2021
    G0CIQ likes this.
  10. G3EDM

    G3EDM Ham Member QRZ Page

    I just bought this little beauty. It was, by the standards of these things, low-priced.

    I've more or less come around to this idea in CW receiver design: Find the right filter, then build your receiver around it, i.e. it's the filter that dictates the IF.

    I now have couple of these types of filter and it will be interesting to decide which one to plump for first. I have another Cathodeon one with a width of 400Hz, which was pulled from decommissioned NATO equipment. CF of that one is 1749 kHz, unfortunately a denominator of the bottom marker of the main HF ham frequencies but there are ways around that.

    Concerning this latest purchase: Isn't 250Hz a little too narrow? Would it tend to "ring" too much? What do you think? I've never used a receiver with a narrow filter, but I assume the procedure is: initially tune into the signal without the filter switched in, then switch it in.


    I'll have to find out the impedances of this filter but I know someone who used to work with these and can probably get the info.

    73 de Martin, G3EDM
    Last edited: Sep 20, 2021
    G0CIQ likes this.

Share This Page