Convert SSB recording on tape to AM?

Discussion in 'Microphones, Speakers & Audio Processing' started by KA2PTE, Aug 12, 2019.

ad: L-HROutlet
ad: l-rl
ad: L-MFJ
ad: MessiPaoloni-1
ad: Subscribe
ad: Left-2
ad: K5AB-Elect-1
  1. AG6QR

    AG6QR Subscriber QRZ Page

    If the 400Hz tone is generated in the audio section of the receiver (or recorder) it should be present when no transmitter is transmitting. If it is coming from an SSB transmitter, it will only be present when the transmitter is keyed up and transmitting audio with two tones separated by 400Hz.

    The clip is too short for me to be sure which of these is happening.
     
  2. KA2PTE

    KA2PTE Ham Member QRZ Page

    Posted the issue in my Electronic Repair BBS, and a new member had this to say :

    "On the ssb broadcast, you could recover it by re-broadcasting it with an AM transmitter, then use two Am recievers and tie the ifs together. Then tune the tuning cap for BFO effect. You could also acquire a 'Product Detector', which goes with a Collins r-390 radio. The model for the Collins version is CV-157, which is real overkill. There are other devices out there that do the same thing."

    So I guess its assuming the IF freq is 455kc, but maybe that gear he mentioned lets you pick multiple IF's. Did a quik search and the Collins seems to be Navy type gear. I guess it boils down to finding someone who owns one of them, and either getting the equipment from them or if they have the capability to do the recovery with the AM rcvrs.
     
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    No, that will not work.

    As has been posted in this thread a number of times the original audio information has been lost. All you have in the case of SSB detected by an AM receiver is the intermodulation products and you cannot simply remodulate those products and recover the original audio signal.

    The recommendation you received to use a pair of AM receivers with IFs chained together and a BFO is just a roundabout way of creating a Double Sideband receiver. Whether using a normal SSB receiver or DSB receiver you cannot use an analog and linear process like remodulation and then alternative methods of demodulation to restore the audio information that was destroyed during the initial detection of an SSB signal in an AM receiver. This particular processing chain is non reversible.
     
    N5RFX, W2VW and AG6QR like this.
  4. KM3F

    KM3F Ham Member QRZ Page

    As TRF said the audio is non retrievable.
    This is basically because the original sideband reference to the original carrier is not able to be reproduced in the exact same relationship for time and relationship.
    This is shown when the VFO is shifted that shifts that relationship on the original radio signal moves the reproduction within the pass band so you hear it as high (missing lows)
    or the opposite missing lows or so far off it sound like Donald duck.
    Even shifting the carrier point on the filter curve shifts the audio reproduction.
    You have no way to know these parameters.
     
    N5RFX likes this.
  5. KM3F

    KM3F Ham Member QRZ Page

    To add another example, if you tune a SSB transmission in on AM then add an external RF cw signal to perform the function as the reference signal, the audio will clear with the right levels and tuning.
    This is the same as using a BFO in the older legacy receivers that mix at first IF mixer. It works the same way to cause a tone to hear CW with. The difference in frequency is the Tone you hear in the audio spectrum. It's all done at the RF level in the chain, not outside by any other "normal" means.
    The mixing before and [then] demodulation with both signals takes place in the detector of the receiver.
    A recording of the SSB signal without the reference signal cannot be substituted 'after' it [becomes audio to the recorder.
     

Share This Page