Digital audio demodulation...

Externet

Well-Known Member

• Jun 14, 2016

• #1

Years ago, two-way radio communications were mostly FM/PM. Now, law enforcement, fire, ambulances... have digital radios.

What is or are the current modulation modes ? I have a very sophisticated receiver but only for AM/FM and would like to know if there is a way to tap its circuitry to monitor public service transmissions (as scanners do) by building a proper demodulator. What would such demodulator would be like ?

 

dr pepper

Well-Known Member

Most Helpful Member

• Jun 14, 2016

• #2

Not sure about the Us, however in the uk the police use tetra, decoding this isnt as easy as that as I'm fairly sure it frequency hops, you need to find out what encryption the transmissions use you want to decode, a encrypted demod would probably need to be at if level.

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Jun 15, 2016

• #3

Does this https://www.motorolasolutions.com/e...os/mobile-radios/apx-7500.html#tabproductinfo help?

 

Externet

Well-Known Member

• Jun 16, 2016

• #4

I was more inclined after whatever is in the guts of something like this :

----> http://www.aorusa.com/others/ard300.html

Seems that one is made to match a specific brand receiver.

 

dr pepper

Well-Known Member

Most Helpful Member

• Jun 16, 2016

• #5

You can get various decoders for sdr#, if you have a pc or laptop at the rx.

 

Externet

Well-Known Member

• Jun 16, 2016

• #6

Thanks.
Can you translate 'sdr#' ?
Is it like a piece of software running in a PC with digital? audio? into its 'audio-in jack' and yielding properly demodulated digital audio out ?
Would such decoders exist for my linux machine ? Wouldn't the receiver signal be better tapped at IF stage ?

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Jun 16, 2016

• #7

SDR = Software Defined Radio; Still certain bands may be unobtainable. https://sdr-radio.com

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Jun 16, 2016

• #8

This https://www.ti.com/solution/software-defined-radio-sdr-diagram isn't cheap.

e.g. https://www.ti.com/lit/ml/sprt435a/sprt435a.pdf

also see: https://en.wikipedia.org/wiki/List_of_software-defined_radios

 

Last edited: Jun 16, 2016

dr pepper

Well-Known Member

Most Helpful Member

• Jun 17, 2016

• #9

This is the one I have, very cheap:
https://www.ebay.co.uk/itm/181637597684?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Sdr is software defined radio yes, but sdr# is actually software designed for the above rx, several decoder modules are available for it:
https://airspy.com/download/

I think you can get it for linux.