Independent Sideband, the forgotten mode

Discussion in 'Ham Radio Discussions' started by KL7AJ, Nov 13, 2008.

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  1. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    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 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" 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.

  2. K4KYV

    K4KYV Subscriber QRZ Page

    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.
  3. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    MOTHER is the necessity of invention. :)

  4. KE4YGS

    KE4YGS Ham Member QRZ Page

    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.

    Last edited: Nov 13, 2008
  5. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

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

  6. K7JEM

    K7JEM Ham Member QRZ Page

    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.

  7. K8ERV

    K8ERV Ham Member QRZ Page

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

    TOM K8ERV Montrose Colo
  8. KB2VXA

    KB2VXA Ham Member QRZ Page

    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.
  9. N2RJ

    N2RJ XML Subscriber QRZ Page

    I think it could be done with modern digital signal processing.
  10. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    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 did exactly what it was supposed to.

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