An Urban Legend Disproved

Discussion in 'Ham Radio Discussions' started by N2EY, Jan 1, 2015.

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  1. W1GUH

    W1GUH Ham Member QRZ Page

    Over the years I've come to view Occam's razor as overrated and overused. Never really made sense anyway.

    Similar to Hanlon's razor, "Never attribute to malice that which can be explained by stupidity."

    Don't subscribe to either anymore.


     
  2. N2EY

    N2EY XML Subscriber QRZ Page

    Nope.

    I used the urban legend as an example, and was asked to expand on it.

    I've posted the disproof a couple of times in various versions in various places.

    I even corrected a mistake in QST some years back, and they posted a retraction. December 2009 IIRC. There was also a sidebar in the 2006 Handbook.
     
  3. W1GUH

    W1GUH Ham Member QRZ Page

    I'm really grateful that you pointed out the myth about sideband selection. I'd taken
    the lazy way out and "believed" all that was necessary was to take the difference and
    never bothered to work out the math which you did so well. Thanks!


     
  4. W9JEF

    W9JEF Platinum Subscriber Platinum Subscriber QRZ Page

    What he said. I too, owing to sloppy thinking, had been repeating that myth. Thanks, Jim.

    The wielding Occam's razor (dull & full of nicks) seems to be a last resort argument, whose validity has yet to be proven.
     
  5. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    I built two sideband rigs using 9 MHZ crystal filters, one was a 6 pole lattice using FT-243 crystals and had a 9 MHZ center frequency and a 3.2 KHZ 6 db bandwidth. for the later one I used a Fox Tango 8 pole 9 MHZ CF and 2.8 KHZ 6 db band width.

    The injection oscillator for the balanced modulator (hot carrier diodes), used two frequencies to generate a DSB signal which, when inserted in the 9 MHZ crystal filter would yield the desired sideband.

    For USB, an injection frequency of 8998.5 KHZ was used and for lower sideband the injection frequency was 9001.5 KHZ. This scheme shifts the desired sideband into the center of the 9 MHZ filter so by simply switching crystals either sideband can be selected.

    The resulting SSB signal was then mixed in a mini-circuits ring diode mixer with a very stable 5 to 5.5 MHZ VFO and either the 80 or 20 meter component was selected using band pass filters. I chose elliptical filters because they have very little ripple in the pass band and are easy to tune. Followed by a 50 watt FET amp and Bobs your uncle.

    So that is the simple SSB transmitter layout, easy to build and fun to operate. The upper or lower sideband can be selected regardless of which band you are on. Other schemes like Drake used a single injection oscillator and two crystal filters in the sideband generator. Instead of shifting the injection frequency the center frequency of the crystal filters are set to pass either the upper or lower sideband. It is a different approach but the idea is exactly the same.

    I encourage anyone who like to experiment with radio to build one. It really is simple and fun, and all of the components are readily available.
     
  6. N2EY

    N2EY XML Subscriber QRZ Page

    I think you meant the January 2015 issue of QST; February isn't out yet.

    Note that in the article they did NOT repeat the mistake of saying that's where the sideband tradition came from!

    Historic trivia:

    We normally associate the transition from separate HF transmitters and receivers to transceivers with SSB. The Cosmophone, KWM-1, KWM-2, etc., all of which date from the very late 1950s (late-1958 and into 1959)

    But note this!

    In QST for May, 1953, W6DSR describes "A Single Control Transmitter-Receiver" in which the receiver section also controls the transmitter frequency, all in a one-box unit, complete except for power supply. W6DSR's unit only covered 40 meters and ran only 25 watts input, but it was a true transceiver in the modern sense, almost 6 years before the SSB transceivers listed above. (In order for the article to appear in the May issue of QST, it had to be pretty much complete by late 1952).

    W6DSR's unit was based on a surplus BC-453....and was CW only. Full QSK, too.
     
  7. K9STH

    K9STH Ham Member QRZ Page

    Collins KWM-1: Late 1956 for 1957 "model year".

    Glen, K9STH
     
  8. W9YAC

    W9YAC Ham Member QRZ Page

    The British WW2 wireless set No. 19, although not an amateur radio, was one of the first true tranceivers that I am aware of. It used some common circuits for both transmit and receive, and used Commercial Off the Shelf components. Some were made for the British by RCA, as I recall.
     
  9. N2EY

    N2EY XML Subscriber QRZ Page

    Yes, the No. 19 was a transceiver in the modern sense - the same oscillator controlled both the receiver and transmitter frequencies. In ingenious fashion, the same oscillator was used for the BFO and transmitter carrier oscillator.

    ---

    It should be mentioned that there was another kind of transceiver in the 1930s and 40s which was used on VHF/UHF. Most designs used three tubes - two in the audio section, and one in the RF section. The RF tube functioned as a superregenerative detector on receive, and as a modulated oscillator on transmit, achieving the ultimate in simplicity. However they had all sorts of drawbacks, the worst being that the detector radiation was sometimes almost as strong as the transmitted signal! After WW2 their use was generall frowned on, and they rapidly disappeared from the amateur bands.

    Sometimes the term "transceiver" is applied to rigs such as the Heath HW-16 and Gonset G-76, as well as many VHF AM rigs. But they are not transceivers in the modern sense; they're really a transmitter and receiver in the same box, with little circuitry in common, and completely separate control of transmit and receive frequency.
     
  10. AC6AT

    AC6AT Ham Member QRZ Page

    [citation needed]
     
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