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SSB Carrier Supression

Discussion in 'General Electronics Chat' started by Space Varmint, Dec 3, 2008.

  1. Electronman

    Electronman New Member

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    Merry Christmas to you all, wish you all the best too.

    Oh so you have used the filter method to attenuate one sideband in this thread.
    But nobody responded to my main question.
    I ant to know how to CREATE SSB-WC really???
     
  2. JimB

    JimB Super Moderator Most Helpful Member

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    Two possible meyhods come to mind:

    1 Generate SSB using your favoured method and then re-insert the carrier.

    2 Generate AM and then use a filter which allows the carrier and wanted sideband to pass, thus suppressing the unwanted sideband.
    The problem with this method is that due to limitations in practical filters you may end up with the low frequency part of the unwanted sideband as well as the carrier and wanted sideband.

    JimB
     
  3. Space Varmint

    Space Varmint New Member

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    I'll tighten you up later. In a big hurry right now but what I just told you before is how it is usually done. You take the audio and a carrier and run it through a balanced modulator. That greatly suppresses the carrier. So now you have a signal with mostly upper and lower sideband and little to no carrier. Then by using a sharp crystal filter set to the frequency of either the upper or lower sideband, you can further attenuate the carrier and because the unwanted sideband is further away from the desired sideband than even the carrier, you essentially scrape that sideband right off so that all you have going out is the desired sideband which contains all the intelligence needed for good voice A3 type modulation.

    I'll put up some schematics on how to do this later when all the Christmas panic is over...:eek::)
     
  4. dave

    Dave New Member

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  5. Space Varmint

    Space Varmint New Member

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    OK, here is a schematic I promised you. The part coming off the microphone is simply an audio amp. At the bottom left is a Hartley VXO which enables me to shift the frequency above or below the 4MHz crystal. By doing this I was able to purchase a hand full of 4MHz crystals to do the whole job instead of ordering an expensive set of crystals for the lower sideband filter. The crystal filter is offset by 1500 Hz. The VXO worked out nicely because frequency stability is crucial to SSB. After I got my signal out of the modulator section (after Xtal filter) I mixed it up to the desired frequency using an up converter circuit configuration which was PLL controlled. Understand that when an SSB signal is being received, the receiver will re-insert a synthetic carrier back into the received SSB signal which now days will more than likely be some sort of digitally locked frequency control. So if you transmitted SSB signal drifts at all, it will be picked up on the receiver end and you are likely to get bitched at because the receiver operator will either have to re-adjust the frequency or if he has a separate BFO tuning control, he will need to re-zero beat your signal.
     

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