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Digital modulation of radio transceivers into amateur use...

Externet

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Greetings.
Radio communications services for fire, police, ambulances and other institutions have migrated to digital modulation modes; which can be of several types from the little am aware. Can anyone provide/point a tutorial to all the methods beyond typical AM. CW, FM, SSB, FSK... in use these days ?

Of all those current digital voice modes, which are in use by the amateur radio groups ? What bands would they be usable or restricted ?
Old radio scanners are partially obsolete uncapable of demodulating these current digital voice transmissions, heading to garbage cans.

Is it that complicated to insert an integrated circuit that decodes/demodulates such transmissions in the reception circuitry path ? Who manufactures those ICs ? Every police 'talkie' has to have such chip inside, right?
 

betwixt

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I would say your best reference is to look up a program called "MULTIPSK" as it documents many of the digital modes and frequencies used. You would be surprised how much amateur digital traffic there is, including digital voice links on HF bands. Because they are unrecognizable to our ears, they are easy to miss but a spectrograph shows them clearly. There are even DRM transmissions carrying high quality stereo music and web pages on frequencies below 4MHz.

True, older receivers will have problems but mostly from their limited audio bandwidths, if you take a feed directly from their detector/discriminator they still work fine. I have a 30+ year old general purpose receiver here to which I've added an IF down-converter (similar to: https://www.eeweb.com/extreme-circuits/drm-down-converter-for-455khz-if-receivers) to give almost DC output to go straight to a PC sound card but you can also use cheap SDR USB sticks to do the same thing for higher frequencies.

Brian.
 

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