No silence on opposite singlesideband SSB...

Discussion in 'General Electronics Chat' started by Externet, Oct 25, 2014.

  1. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    With a properly tuned signal on -say lower sideband- ; when upper sideband is selected on the receiver, some (inverted) garbled audio is still detected.
    Why is there no silence ?
    Is it a flaw in the demodulator circuit design,
    or is that the nature of the beast,
    or is the received transmitter signal flawed in its SSB modulation,
    or ?

    Please educate me on how to obtain silence. Just built a circuit that adds a second SSB demodulator from the same 455 KHz IF in a receiver (Kenwood R-1000) to simoultaneously obtain both separate sidebands audio and almost ready to insert such in the receiver circuit.

    But think that may not work properly; and before going further into tapping/splitting signals in the receiver circuitry, would prefer opinions. The goal is to obtain the audio from one sideband and silence (or normal atmospheric noise QRN) on the other.
  2. bertus


    Apr 5, 2008
  3. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    Thanks, Bertus.
    The signal heard on the opposite sideband is the same as in the correct sideband. Just lower in amplitude and inverted, but belongs to the same received signal, not an interference from another transmission.
    The 'tests' were performed when no other stations were in the sorroundings of the tuned frequency. The 'unwanted' audio on the opposite sideband corresponds as mirror image of the 'wanted' audio. I was expecting silence. :(
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Your filter does not have steep enough skirts. (I know, I own a R1000 (analog filter) and a modern DSP-based Yaesu ham rig. I do not hear the opposite sideband on the Yaesu...)
  5. BR-549

    Well-Known Member

    Sep 22, 2013
    May I ask what frequency you are on? You might get the same result even with a perfect receiver. When the skip is's hard to find 2k of silence on some bands.
  6. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    Thanks, MikeML.
    On my Kenwood TS-440, cannot hear the opposite sideband either. But I have no 'balls' to modify this one, as the divider chip for the PLL that handles the carrier reinsertion gets the divide data briefly and latches it. Too complex to tamper with.
    The R-1000 was a good candidate. Any suggestion to improve its filter skirt to stop the unwanted bleeding ? It has two oscillators, 453.4 and 456.6 KHz.
    By 'unintended feature', both work simoultaneously by pressing both USB and LSB mode buttons, but the audios are summed as there is only one demodulator.
  7. Externet

    Thread Starter AAC Fanatic!

    Nov 29, 2005
    I go to any frequency in the HF band with SSB activity without crowding, to be able to discern a single signal and avoid adyacent interference. And got the unwanted bleeding from the R-1000.
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
    what level was the signal you were recieving? no filters are 100%effective at removing the oposite sideband. it might be strong enough to recieve. also your recieve filter might mot be 100 % effective also.