SSB-SC can be seen like narrow FM?

[neazoi]

Hello,
Thinking logically I would like to ask something:

The SSB-SC modulation can be "seen" on the receiver side like a narrow-FM modulation?

What I mean is that, If you see the SSB-SC signal it is like a signal that continuously changes it's frequency (within 3KHz or so) in and out of the suppressed carrier. Of course it changes also it's amplitude, but the radioamateurs tend to use audio compressors to keep the amplitude stable and hense maximize the transmitted output.

Why not making a narrow FM transmitter which is easier to make and to replace the SSB-SC one? This transmitter would achieve full power at all times and avoiding any sidebands at all. The carrier can be then switched on with a relay only on the transmit times.

Would that work?

 

[tony_lth]

Single SideBand Modulation
SSB-SC is analog modulation, this is simpler than FM, digital modulation.
SSB-SC need one carrier, but FM need two carriers.

 

[neazoi]

Single SideBand Modulation
SSB-SC is analog modulation, this is simpler than FM, digital modulation.
SSB-SC need one carrier, but FM need two carriers.

This is a nice example. I am talking about narrow FM, not FSK. By the way FSK does not use two carriers, it just shifts the carrier by a predefined amount (using possibly a varicap) to denote zeros and ones.
If you notice the website you have just sent, you may see that in fact SSB behaves like FM, and in the case where an audio compressor is used ssb behaves like FM, as no significant variations in the amplitude of the signal occur.

This is the consideration I would like to discuss.
By using a single varicap you can modulate the carrier FM (for voice comms) and if you keep the deviation at 3KHz this is SSB! Depending on the type of diode also you can reduce the carrier frequency or increase it, which gives USB and LSB.

If this consideration is true and you "see" the FM carrier as one of the two sidebands in SSB, then using this method you may achieve an SSB signall with no carrier and sideband at all! This would be the perfect SSB signal and it needs absolutely no SSB filters!! Plus, simple class-C amplifiers can be used as in the FM band, which maximizes efficiency.

What do you think of this?

 

[keith1200rs]

A NBFM spectrum looks a bit like AM, not SSB. It has a carrier and two sidebands. When I first started haming on VHF I interfered with my parents TV so tried FM (almost everyone else used AM - there wan't much SSB on VHF back then). All the AM guys had no problems listening to me on their AM receivers. They had to tune slightly off frequency so the frequency deviation produced and amplitude deviation at the edge of the IF filter, I think.

The same won't work for SSB/FM - the spectra are totally different.

Keith

 

[neazoi]

A NBFM spectrum looks a bit like AM, not SSB. It has a carrier and two sidebands. When I first started haming on VHF I interfered with my parents TV so tried FM (almost everyone else used AM - there wan't much SSB on VHF back then). All the AM guys had no problems listening to me on their AM receivers. They had to tune slightly off frequency so the frequency deviation produced and amplitude deviation at the edge of the IF filter, I think.

The same won't work for SSB/FM - the spectra are totally different.

Keith

Yes you can detect FM on an AM receiver that way indeed.
But I do not understand why FM has sidebands? The method of FM modulation I am talking uses a varicap to change the frequency of the FM carrier, the varicap changes it's capacity by an audio signal applied to it. No mixing is done there, you just shift the unmodulated carrier to produce FM. It is the same technique used on these pirate fm tube transmitters, although the deviation was much bigger there as Wideband FM was needed.
So I cannot see why this signal has sidebands?

Why transmitting narrow-FM (3KHz) shouldn't be the same as transmitting SSB-SC (the carrier and the unwanted sideband miising)?
All I do is, I am thinking of the FM carrier as the USB in an ssb signal.

 

[keith1200rs]

Here is the spectrum of NBFM

To understand the spectra you need to turn your equations for the modulated carrier into the frequency domain by fourier transform. That will be covered in books, although there should be examples on the internet. Your theory that NBFM simply creates a SSB like spectrum is incorrect.

Keith

 

[neazoi]

Thank you keith