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

    'DPO:

    Reason for that is Drake, at least in the TR-3, made the two filters asymmetrical. The skirt was steeper towards the carrier for carrier suppression and shallower away from the carrier for good sounding audio.
     
  2. W9JEF

    W9JEF Platinum Subscriber Platinum Subscriber QRZ Page

    My first SSB transceiver was a used Swan 175 (3.8to 4.0, LSB).
    Upper sideband generated at around 5 MHz, VFO around 9 MHz.
    With the addition of 3 bandswitches (and a trimmer cap
    for the VFO) it covered 14.1 to 14.3 (or was it 14.2 to 14.4?), USB.
    And the VFO tuning dial wasn't bass-ackward. Can't help wondering why
    Swan didn't add those few parts, and sell it as a 2-band radio.
     
  3. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    That's interesting but it does make some sense if the carrier suppression in the balanced mod was that poor in the TR3. I have a T4XB and the filters are pretty symmetrical, I checked them with a sweep generator and spectrum analyzer. I guess they improved the modulator since the carrier is like 46 db down on my transmitter.
     
  4. W1GUH

    W1GUH Ham Member QRZ Page

    I never really knew how much the filter contributed to carrier suppression in any
    filter type rig. Sounds like an interesting topic to research!
     
  5. N2EY

    N2EY XML Subscriber QRZ Page

    Because the Swan monobanders were being sold as absolute rock-bottom-priced rigs.

    Note that soon after the monobanders came out, Swan produced the 240, which covered 75/40/20. Somebody probably realized that with the addition of 3 position switches and a few parts, they could hit all three bands with one rig.

    The use of a ~ 5 MHz SSB generator and a VFO at either 9 or 12 MHz gave them 75, 40 and 20 with the "correct" sideband, automatically.
     
  6. N2EY

    N2EY XML Subscriber QRZ Page

    I think the real reasons for the way Drake did it in the TR-3 and TR-4 aren't about carrier suppression. I think they are:

    1) Asymmetrical filters maximized the unwanted-sideband suppression without cutting off the highs too much on the desired sideband.

    2) Switching the filters meant that the carrier oscillator crystal and the PTO frequency could be the same for both sidebands. This meant simplicity in those circuits and a more-accurate dial.

    3) The designers may have decided that the extra cost of the added filter was justified by the savings and performance improvements elsewhere.

    4) Unless I am mistaken, the TR-3 was Drake's first venture into building ham equipment that would transmit. It was a big leap, coming out with a transceiver to compete with the Collins KWM-2. Much of what we now take for granted as standard practice was cutting-edge stuff back then, at least for amateur gear.

    ---

    IMHO, it was the introduction of SSB transceivers and grounded-grid linear amplifiers which caused SSB to displace AM as the most-popular voice mode on the amateur HF bands in the early 1960s. I think that transceivers, and to a certain extent matched-pair separates that could transceive, tipped the scales in both cost and operating ease. Hams had been using SSB since the 1930s, and it had achieved significant popularity in the 1950s, but it was still a rather expensive mode to implement, and the task of zero-beating was much more difficult than with AM. Transceivers and grounded-grid linears turned the whole picture upside-down - for the price of a 100 watt AM station, one could have a kilowatt SSB setup that was smaller, lighter, and in many ways easier to use.

    IMHO
     
  7. SM0AOM

    SM0AOM Ham Member QRZ Page

    Making filter slopes asymmetrical does not change the audio response very much, as phase distorsion effects are primarily confined to the
    edge of the passband, and what happens in the transition band contributes little to this.

    The filter slopes in the TR-3 were mainly dictated of what you could get when using only a 4-pole filter.

    When there are few filter poles, you may have to make a trade-off between opposite-sideband rejection or symmetrical skirt selectivity.
    The TR-4 used 8-pole filters with symmetrical responses. Symmetrical responses with good shape factors are much easier to realise with a larger number of poles.

    73/
    Karl-Arne
    SM0AOM
     
  8. N2EY

    N2EY XML Subscriber QRZ Page

    Thanks, Karl-Arne! Makes perfect sense.

    I did not know that the TR-3 used 4 pole filters vs. 8 poles in the TR-4. Major improvement!
     
  9. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    It wasn't long after that that Swan got seriously competitive. I remember in the 1960's they were in a war with Yaesu, seemed like each company came out with a new, better, higher power rig every six months. Both Swan and Yaesu really put affordable single sideband transceivers on the map and amateur radio never really looked back.
     
  10. N2EY

    N2EY XML Subscriber QRZ Page

    Swan was in the US market a few years ahead of Yaesu. The "wattage wars" happened in the late 1960s and into the 1970s - not sure who actually "won".

    As for affordable SSB transceivers, there were a lot of players in that game. Heathkit was a major one - their single-banders cost less than $100! The SB-100/1/2 family, the HW-100, and in particular the HW-101 were available at rock-bottom prices. Yes, you had to build them, and Heath avoided the wattage wars, but in the late 1960s you could get an HW-101 and power supply for under $300.

    There were also rigs like the NCX-3 and National 200, which did a decent job on SSB at relatively low prices.

    No list of low-cost SSB gear would be complete without mentioning the WRL DB-84 and the (in)famous Eico 753...

    ----

    Edited to add: Swan was indeed a major player in the ham rig SSB transceiver market of the 1960s and 1970s. In fact, when you look back to those days, there were a lot of companies making HF SSB transceivers for hams. Consider just the USA rigmakers: Collins, Drake, Heathkit, Swan, National, Hallicrafters, WRL/Galaxy, to name just the ones I remember now. There were probably others.

    It should also be remembered that some Japanese made gear was sold in the USA under US brand names. The Henry Tempo One was a rebadged Yaesu FT-200; the Allied A-2517 was a rebadged Trio/Kenwood product, to name just two.
     
    Last edited: Jan 9, 2015
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