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Wednesday, February 12, 2014

A Very Simple SSB Transmitter

 
 
I found this in the files section of the BITX20 Yahoo Group.  There is no information on the source.  I see two balanced modulators and two very simple phase shift networks. 


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3 comments:

  1. Bill - Looks like a solid state version of ZL2AMJ's first Tucker Tin (c1962) - the two tube SSB transceiver designed for use with a carbon microphone. Also one of the Doug Demaw books (QRP Notebook?) had a phasing SSB tx circuit as an idea to try but with few details. 73, Peter VK3YE

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  2. I was going to say, that simple a transmitter was not uncommon in the old days.

    One thing about using phasing for transmitting is that you have a controlled source. Actual voice is a small bandwidth, and you can use a limited bandwidth microphone and/or audio shaping to keep out extra frequencies like from fans.

    This means the phasing network doesn't have to handle wide bandwidth, indeed the worst that can happen with a simple phasing network is that you may put out something on the unwanted sideband.

    So those rigs were in effect a hybrid, better than DSB (that were also common for similar reasons) in that some of the other sideband was gone, but not that much more complicated. Though DSB had the advantage of being done at high levels, while most phasing rigs were done at low level and amplified.

    With a receiver, you're faced with all that is there on the band. If you don't knock out the sideband with a good phasing network, you get interference from the "audio image". And since there's nothing really to limit what the phasing network has to handle in the receiver, it has to be better than on a simple transmitter.

    I remember an article in "73" about ISB from 1977, it said something about how the phasing method wasn't likely to be useful. I read that again a few years after that, and realized that if you were sending RTTY on the other sideband, that would be so simple. You don't need a phasing network, just generate the tones with some circuit that puts out a quadrature output. Easier to start with the right signal than to put a regular oscillator through a phasing network. Of course, that really only works when you need only an oscillator output. Voice is too complicated.

    That was before phasing made a real comeback as serious transmitters, in between the early work on SSB and ore recent times, it was seen as a simple method for getting sideband.

    Michael

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  3. It looks almost identical to the one on page 164 of W1AW's QRP Notebook. He said it was his interpretation, from an old book, of a tube version, someone had asked him make a solid state version.

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