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Thread: Independent Sideband, the forgotten mode

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  1. #1
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    Default Independent Sideband, the forgotten mode

    Independent Sideband has great possibliities for amateur radio. Back in the 1970s there was some flirtation with the technique (see May, 1977 QST) but it never really caught on. The main application was with SSTV...you could send your photos on upper sideband and audio on lower sideband. It was actually quite a lot of work to set this up...but with new DSP techniques it should be a snap.

    But I see something even cooler about ISB. With a very well aligned system, you could run FULL DUPLEX SSB on HF. (Maritime radio has used full duplex H.F. for years, but with widely separated channels. With a good ISB system, ou could talk and listen at the same time on the same "carrier" frequency...one direction on usb and the other on lsb. With a high isolation hybrid or circulator, you could even use the same antenna. I think this is something worth experimenting with.

    Eric
    "The more you know, the less you don't know."

  2. #2
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    Armed Forces Radio and VOA used to run feeder links to their overseas stations using HF ISB. They could be heard on odd frequencies outside the regular shortwave broadcast bands. You could hear one program on USB and another on LSB. This was before the days of long distance transmission by satellite.
    Hard Core AM since 1959

  3. #3
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    Quote Originally Posted by k4kyv View Post
    Armed Forces Radio and VOA used to run feeder links to their overseas stations using HF ISB. They could be heard on odd frequencies outside the regular shortwave broadcast bands. You could hear one program on USB and another on LSB. This was before the days of long distance transmission by satellite.
    MOTHER is the necessity of invention.

    eric
    "The more you know, the less you don't know."

  4. #4

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    Maybe it isn't necessary but I can envision the need for a timing chain somewhere for both sets to lock onto for really accurate signal processing. Maybe transmitted by the TX terminal and the Rx terminal locks its PLL, ref osc or its LO to it and vice versa so there is no freq disparity. Maybe I'm a victim of the modern age. I seem to remember some Navy testing circa. 1968-9 where they tried USB for voice and LSB for TTY. I think the intent was the same as a primitive orderwire on Satellite Links. Raven Electronics was working with the Navy on it. Was a dismal failure as I remember. I can think of several ways to make it work but they all involve dollars in fairly significant quantity compared to the cost of the radio. Voice of course, as in full duplex voice would be much less touchy.

    Scotty
    Last edited by KE4YGS; 11-13-2008 at 07:00 PM. Reason: spelling

  5. #5
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    Quote Originally Posted by KE4YGS View Post
    Maybe it isn't necessary but I can envision the need for a timing chain somewhere for both sets to lock onto for really accurate signal processing. Maybe transmitted by the TX terminal and the Rx terminal locks its PLL, ref osc or its LO to it and vice versa so there is no freq disparity. Maybe I'm a victim of the modern age.

    Scotty

    In an ISB transmitter, you use the same generator...they WILL be locked.

    eric
    "The more you know, the less you don't know."

  6. #6
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    Quote Originally Posted by kl7aj View Post

    But I see something even cooler about ISB. With a very well aligned system, you could run FULL DUPLEX SSB on HF. (Maritime radio has used full duplex H.F. for years, but with widely separated channels. With a good ISB system, ou could talk and listen at the same time on the same "carrier" frequency...one direction on usb and the other on lsb. With a high isolation hybrid or circulator, you could even use the same antenna. I think this is something worth experimenting with.

    Eric
    I don't think that would work. You still have a strong transmitted signal very near the RX signal. This would cause extreme overload to the RX side. A hybrid or circulator just isn't going to be enough. Even opposite sideband suppression would have to be immense, generally it is only about 50dB. Even 100dB wouldn't be enough.

    Joe

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    I was associated with a 10kw Collins xmitter on Eniwetok. The two sidebands carried separate (multiplexed) RTTY channels. Why not?

    TOM K8ERV Montrose Colo

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    Hmmm, sounds like the Kahn mono compatible AM stereo system. I know where there's an exciter siting in a rack just waiting to be re tuned for 160M and fed into a 1KW transmitter already there but alas, that'll never happen.
    I don't suffer from insanity, I enjoy every minute of it.
    73 de Warren KB2VXA

  9. #9
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    Quote Originally Posted by K7JEM View Post
    I don't think that would work. You still have a strong transmitted signal very near the RX signal. This would cause extreme overload to the RX side. A hybrid or circulator just isn't going to be enough. Even opposite sideband suppression would have to be immense, generally it is only about 50dB. Even 100dB wouldn't be enough.

    Joe
    I think it could be done with modern digital signal processing.

  10. #10
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    Quote Originally Posted by kb2vxa View Post
    Hmmm, sounds like the Kahn mono compatible AM stereo system. I know where there's an exciter siting in a rack just waiting to be re tuned for 160M and fed into a 1KW transmitter already there but alas, that'll never happen.
    Funny you should mention that. I talked to Leonard Kahn once, about 20 years ago. He was a cranky eccentric back then, and I guess he's still going strong. He made some fine equipment though. We had a Symmetra-Peak on our FM station for ages....it did exactly what it was supposed to.

    eric
    "The more you know, the less you don't know."

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