Scrambled FM can be heard from SSB RX?

scrambled FM can be heard from ssb RX?

Hi, my friend has these cheap Asian VHF/UHF FM handheld transceivers, that have analogue scramblers (voice inversion) embedded.
If he talks FM with the scrambler ON, will an SSB receiver be able to listen and understand his conversations?

Re: scrambled FM can be heard from ssb RX?

you say "voice inversion" as if that was some well kown engineering term, which it is not.

Re: scrambled FM can be heard from ssb RX?

Motorola uses the same term for the scrambler option on some of its VHF radios.
https://www.manualslib.com/manual/560437/Motorola-Cp185-Series.html?page=20

https://en.wikipedia.org/wiki/Voice_inversion

Re: scrambled FM can be heard from ssb RX?

E-design said:

Motorola uses the same term for the scrambler option on some of its VHF radios.
https://www.manualslib.com/manual/560437/Motorola-Cp185-Series.html?page=20

https://en.wikipedia.org/wiki/Voice_inversion

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So what is the answer in the question? I suspect ssb receivers won't be able to understand it.

Re: scrambled FM can be heard from ssb RX?

There are different ways of doing the inversion. Some use split-band inversion which is a higher level of scrambling. I can't find any material that suggest you would be able to listen to the scrambled conversation using just a SSB receiver.

https://www.windytan.com/2013/05/descrambling-voice-inversion.html

Re: scrambled FM can be heard from ssb RX?

Your buddy's radio is FM, a SSB radio is AM - although it is possible to slope-detect an FM signal. It therefore can be received, demodulated and properly decoded on a SSB radio, if the operator has enough control over the SSB radio's operation.

Re: scrambled FM can be heard from ssb RX?

SLK001 said:

Your buddy's radio is FM, a SSB radio is AM - although it is possible to slope-detect an FM signal. It therefore can be received, demodulated and properly decoded on a SSB radio, if the operator has enough control over the SSB radio's operation.

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If a full mode inversion (i.e the whole audio passband inverted) is done on a USB TX, then the RX can just switch to LSB and shift the RX frequency above that of the TX, so that it can understand the intelligence.
However, it is not clear to me why if the same inversion mode is applied to an FM TX, why it can be understood on an SSB RX.
How can it be, since the two modulation schemes are not compatible. An SSB is an amplitude AND frequency variation modulation scheme.

Re: scrambled FM can be heard from ssb RX?

neazoi said:

How can it be, since the two modulation schemes are not compatible. An SSB is an amplitude AND frequency variation modulation scheme.

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Look into slope detection. It is a low fidelity conversion of a constant envelope signal (FM) by an AM receiver. To do it, you need full control of your SSB receiver (RX freq, etc). If you tune the SSB slight off frequency of the RX signal, the frequency deviation of the signal will begin to look like amplitude modulation, which a SSB AM receiver can demodulate.

I used to slope detect the audio signal from local TV transmitters with a spectrum analyzer's AM demodulator.

Re: scrambled FM can be heard from ssb RX?

SLK001 said:

Look into slope detection. It is a low fidelity conversion of a constant envelope signal (FM) by an AM receiver. To do it, you need full control of your SSB receiver (RX freq, etc). If you tune the SSB slight off frequency of the RX signal, the frequency deviation of the signal will begin to look like amplitude modulation, which a SSB AM receiver can demodulate.

I used to slope detect the audio signal from local TV transmitters with a spectrum analyzer's AM demodulator.

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I see. So he can tune to the signal by the LSB and slope detect it. However I doubt that the recovered signal will be good with slope detection. It might be but it might be of low level, possibly not enough to even open the squelch.

Re: scrambled FM can be heard from ssb RX?

If I understand the question: you are asking if unscrambling an FM 'spectrum inverted' signal by using the opposite sideband in an SSB receiver (so a dual inversion) is possible.

The answer is no, the reason is the FM signal no longer has sidebands that are related in amplitude and frequency to the original signal. An AM signal has a spectrum of carriers related to the difference between the center frequency and modulation frequency (carrier + modulation and carrier - modulation) and if one is removed to make SSB, it can be recovered by mixing with a locally generated carrier (BFO for example) in the receiver. FM spectrum is quite different, the speed of sideband movement rather than it's absolute frequency carries the modulation and it isn't possible mix it to recover the opposite sideband.

Certainly you would hear something but I doubt it would be intelligible, probably just bursts of noise in time with the audio.

Brian.

Re: scrambled FM can be heard from ssb RX?

Here is a video that suggests that it may be possible to listen in using an SSB mode receiver. It is unclear if this was performed on simple inversion or split-band encryption. I suspect it must on simple inversion.
https://www.youtube.com/watch?v=A_S2U7Uy1zc&t=8s