Double sideband demodulations - How to ?

[Externet]

Can anyone point me to a radio receiver circuit that will demodulate both upper sideband and lower sideband simultaneously each to independent audio signals so they will end in two speakers ?
-Suppressed carrier-

 

[mvs sarma]

In general double sideband suppressed carrier transmissions are redundant in sidebands. they contain same information, thus it is always preferred to transmit only one sideband, suppressing the other. you can, perhaps choose any one,at the transmitting end.
at Receiving end,the difference between s side band and carrier is taken, irrespective of sign.thus a difference between a carrier of 100KHz and usb of range from 100.03 to 110KHz is trated as 30Hz to 10KHz neglecting the sign.

In case of LSB, again the difference between100KHz and the LSB range of 99.97 to 90 Inverted as it shows up becomes 330HZ to 10KHz (watch the inversion recovered.)
Hope I am clear
if needed i am at your service to show more examples.
if both are transmitted, perhaps we need to select one of the sidebands and process them accordingly. I am told that in certain countires there are AM stereo transmissions available using double sideband suppressed carrier.
then perhaps filter each sideband and process independently and recover the audios separately and feed to stereo amplifier, though I am not sure of exact method used. otherwise , in Mono , there appears no point in transmitting both sidebands, as they contain same information and it would amount wasting power in RF amplification and band occupancy for no reason.

 

[Externet]

Thanks for responding.
The transmission does not matter at all how it may be, having same, different or no information in one is irrelevant to my question.
Am after receiving both sidebands.

I believe I need two detector circuits from the same IF, each fed with an equally shifted carrier; one higher and one lower than the suppressed carrier to obtain both audio signals, resulting in
same audio on both;
or different,
or audio and silence.

But a typical receiver has only one carrier generated by its osc/VCO/PLL. I suppose a second osc/VCO/PLL circuit would also be needed to implement.
-Please correct me if wrong-

But would like to know if someone has seen/suggests another approach.

 

[Nigel Goodwin]

You simply need to reinsert the carrier, the two sidebands shared a common carrier during creation and need to share the same one to reverse it.

 

[mvs sarma]

How would you receive a non-existent signal?
in general if carrier is present , just detection is sufficient and you get audio with a LPF filtering out the IF.
if some has deliberately sent two different signals one as LSB and another as USB with same carrier, your reasoning stands justified.

carrier is Only one, but the input RF ( either upper or lower filtered by a individual filter) is presented in each case.
if the transmitting end transmits only one side band, you need to know and filter that.

 

[JimB]

A receiver for double sideband suppressed carrier, where the sidebands are independant of each other, will have two IF amplifiers, detectors and audio stages.
One of the IF amplifiers will have an LSB filter, the other will have a USB filter.
They will use a common carrier insertion oscillator in their demodulator stages.

To find more information on the world wide interweb, try googling for "independant sideband" or "isb".

JimB

 

[mvs sarma]

perfect , JimB

 

[Externet]

Thanks, fellows !

JimB; the terminology you used and I did not know: ISB helped greatly to confirm what I believed; as shown in Fig. 1 - B at ----> https://www.electro-tech-online.com/custompdfs/2011/07/qst5-77.pdf
(ignore the Tx sections of the block diagram)

In short words takes two receivers, with different BFO frequencies.

I just ordered the assemblies to add a second identical VCO/PLL board and a second identical IF-product detector board to my HF rig.

In preliminary tests, I used a Kenwood R1000 in USB and a Kenwood TS440S in LSB, monitoring each audio output in the 2 channel oscilloscope in A-B mode when both tuned at the same supressed carrier.

Had to order the boards as the test receivers being slightly different, I got 10 µS delayed audio on the 440; yielding both audio signals not coincidental in time and I need them in phase.

 

[Nigel Goodwin]

Thanks, fellows !

JimB; the terminology you used and I did not know: ISB helped greatly to confirm what I believed; as shown in Fig. 1 - B at ----> **broken link removed**
(ignore the Tx sections of the block diagram)

In short words takes two receivers, with different BFO frequencies.

It depends entirely on the design, but only one receiver is required with a single BFO, or two receivers with the same BFO frequencies (as long as it used seperate filters for upper and lower sidebands). Different BFO's frequencies would only be required for receivers that switched different BFO frequencies to select diffferent sidebands.

I just ordered the assemblies to add a second identical VCO/PLL board and a second identical IF-product detector board to my HF rig.

In preliminary tests, I used a Kenwood R1000 in USB and a Kenwood TS440S in LSB, monitoring each audio output in the 2 channel oscilloscope in A-B mode when both tuned at the same supressed carrier.

Had to order the boards as the test receivers being slightly different, I got 10 µS delayed audio on the 440; yielding both audio signals not coincidental in time and I need them in phase.

What exactly are you trying to do?.

 

[Externet]

Thanks.
Yes, that is the case:

" Different BFO's frequencies would only be required for receivers that switched different BFO frequencies to select diffferent sidebands"

The receiver to have the modification implemented has only one SSB filter, and shifts the BFO to select the chosen sideband.

A PM will follow.