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Tenchi

Receiving digital broadcasts

4 posts in this topic

Hey everyone,

I was digging around the attic last week (looking for a SW radio, alas I couldn't find one) and I came across an old, cheap radio scanner I used to listen to aircraft. A bottle of whiskey later and I was disappointed to find that most broadcasts are digital these days. Or at least I'm guessing from the pain in my ear :P

Would listening to these be a simple matter of hooking up a modem and getting ASCII? Or are they all encoded/encrypted? Or perhaps there is another cheap hack I could employ.

I've flicked through quite a number of posts today in this forum but I'm sorry to say RF is not my area of expertise!

Any advice much appreciated

Tenchi

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Hey everyone,

I was digging around the attic last week (looking for a SW radio, alas I couldn't find one) and I came across an old, cheap radio scanner I used to listen to aircraft. A bottle of whiskey later and I was disappointed to find that most broadcasts are digital these days. Or at least I'm guessing from the pain in my ear :P

Would listening to these be a simple matter of hooking up a modem and getting ASCII? Or are they all encoded/encrypted? Or perhaps there is another cheap hack I could employ.

I've flicked through quite a number of posts today in this forum but I'm sorry to say RF is not my area of expertise!

Any advice much appreciated

Tenchi

Aircraft transmissions are in AM tho you can still pick them up with a FM receiver....

There is alot of Analog Voice traffic out there. *ALOT*. That said, yes, there is digital traffic as well. Pagers, Mobile Data Systems, etc...

No. It's not as simple as plugging in your analog modem to your radio and *magically* decode these signals.

First, there's modulation: (A)FSK,PSK,MSK,etc...

Then there's protocol: POGSAG,MDS,AX.25,ACARS,GSM,etc...

Then if you're able to conquer both of these two... there *might* be encryption depending on application (ie: Military, Public Safety)

Probably the first thing you'd want to do is identify what is being transmitted with what's known. There are many sites out there that have "samples" of digital transmissions. Try and find a match then build up your knowledge from there.

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If you are wanting to listen in on 'ASCII' traffic, such as pagers/APRS/etc, then you can feed the audio from your scanner into a computer's sound card and decode it in software. The application I would use in Linux is called Multimon (http://www.baycom.org/%7Etom/ham/linux/multimon.html), which understands/demodulates AFSK, HAPN, FSK, POCSAG, DTMF and ZVEI.

You can get better performance by adding a descriminator output to your scanner, but this requires some soldering experience and may not be possible on your model.

If you are trying to listen to the more advanced digital modulation and encoding schemes I think you are going to be out of luck.

Mungewell.

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If you are wanting to listen in on 'ASCII' traffic, such as pagers/APRS/etc, then you can feed the audio from your scanner into a computer's sound card and decode it in software. The application I would use in Linux is called Multimon (http://www.baycom.org/%7Etom/ham/linux/multimon.html), which understands/demodulates AFSK, HAPN, FSK, POCSAG, DTMF and ZVEI.

Thank you so much! I was hoping to post with some results, but I've spent the last couple of nights struggling with my onboard sound chip under linux. I found Multimon in the Ubuntu repositories though, so a simple apt-get hooked me up (it even comes with man page). And I've got some natty wiring for my scanner in another room (computers generate crazy noise eh) with headphones and PC feed. I'll keep plugging away at it!

You can get better performance by adding a descriminator output to your scanner, but this requires some soldering experience and may not be possible on your model.

I just learnt a whole load about RF receivers right there, thanks for the tip. I'm no stranger to soldering and I used to tinker with my CB radio when I was young (some crazy roger-bleep contest).

If you are trying to listen to the more advanced digital modulation and encoding schemes I think you are going to be out of luck.

Mungewell.

Maybe one day!

Thank you also jfalcon for the info on modulation and protocol. I didn't expect anything automagically, I just figured (with my limited knowledge) if something was to demodulate a data signal a modem would be the kiddie :)

Are there active groups engaged in this kind of scanning, or is it considered a bit weird?

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