Data on the air. How's it encoded?

[C222]

While listening to radio waves on my brand-new scanner I got for Christmas/holidays/Festivus, I came across some noise that sounded like a datastream. I have heard BPSK31 and QPSK31 before and this didn't fit the bill. I have uploaded a clip to my server : http://www.tehcr3w.com/data.wav

If anyone has any idea what encoding this is, I'd love to hear it.


P.S. It suddenly broke out into Morse then didn't go back. Huh. (edit: the Morse came again and said, "TPVQ329 2 G" I have no idea.)

[Al Skierkiewicz]

C,
It would help to know what frequency you were receiving this message. Don Rotolo is the digital on air expert. I will alert him of this thread.

[Dave Flowerday]

Originally Posted by C222

P.S. It suddenly broke out into Morse then didn't go back. Huh. (edit: the Morse came again and said, "TPVQ329 2 G" I have no idea.)

Many types of transmitters are required to transmit a Station Identification in Morse code by the FCC every so often. I work at Motorola on digital trunked radio systems and our systems have the capability to transmit a Morse code station ID in between digital transmissions to meet FCC requirements.

The audio clip you posted sounds like either a paging system or a trunked radio channel to me.

[DonRotolo]

I couldn't ID that immediately. Check http://www.kb9ukd.com/digital/ for a list of what several digital modes sound like.

I agree with Dave, this is a paging system or perhaps a telemetry system, since the messages being sent are very short and infrequent. Knowing the frequency is a huge help, since that gives you a clue as to who is allowed to transmit there... Being heard on a scanner, I'm guessing it was in the 150-160 MHz range, which fits with paging.

I did a search on the morse ID you gave, but the FCC has never heard of it, so it may be a station ID (check the timing - it's an ID if it comes just under every 10 minutes).

We can definitely find exactly what this is, with some additional info.

[ebarker]

Does a trunked system sound anything like this ?

[rsisk]

You gotta love the HAM community, very much like the CD community. They are all very smart, and love to share.

So, what is a trunked system?


KE6NTE

[DonRotolo]

It can be a control channel for a trunked system, but it just doesn't seem right, the amount and quantity of information seems too low/slow.


What is a trunked system? Of course, you can google or wikipedia it.

In short, when you have many radio users, but not many channels, you 'trunk' all the voice signals onto a few shared channels and tell the receiving radio where to listen. The radio tuner hops around for its signal, and you can pack a lot more signal into just a few radio channels this way. Trunked systems also allow interoperability, the ability of one group of users to speak with another group if users, but can suffer from overload when there are a large number of users needing access at the same time in an under-designed system.

[C222]

Originally Posted by Don Rotolo

Being heard on a scanner, I'm guessing it was in the 150-160 MHz range, which fits with paging.

Yup, it transmitting at 152.840 and the paging idea makes sense. It's still transmitting loud and clear today at noon. It also seems busier. Also my loacation is: CM97as if that helps.

edit: Also, it seems that the paging Modes have "noisy" data encased between beeps. At the moment, POCSAG 512 baud looks the most promising.

edit again: i got an application that decodes POCSAG and it works intermittently. I have recieved some interesting text. The morse also came again and said: WPVQ32E22

[DonRotolo]

OK, that all fits.

Go to the FCC page I quoted in Post 4, type in WPVQ32 and hit Search.
I chose WPVQ322 and found it is registered to Cook Telecom in San Francisco, authorized frequencies between 152.825 and 152.855 for service CP (Part 22 VHF/UHF Paging).

POCSAG is by far the most popular paging protocol, and the fact that you can decode ANY data proves that you have the right one - if it was something else you'd get nothing.

Originally Posted by C222

While listening to radio waves on my brand-new scanner I got for Christmas/holidays/Festivus, I came across some noise that sounded like a datastream. I have heard BPSK31 and QPSK31 before and this didn't fit the bill. I have uploaded a clip to my server : http://www.tehcr3w.com/data.wav

If anyone has any idea what encoding this is, I'd love to hear it.


P.S. It suddenly broke out into Morse then didn't go back. Huh. (edit: the Morse came again and said, "TPVQ329 2 G" I have no idea.)

THAT is a paging channel and that noise is paging data, off the top of my ears I can't remember what format of paging but it is alpha-numeric type paging data for sure, I work in news and monitor emergency services on many scanners and we have a couple of nasty VHF paging transmitters that blast that crap out all the time and thats what it is.

Now a good source of frequencies, trunked systems, etc can be found at www.radioreference.com

Not sure what type of scanner you got but hopefully it is a digital (apco 25) scanner. Not all emergency services are going P25, some use other NON-SCANNABLE digital formats or encryption as well keep in mind.

m

Originally Posted by ebarker

Does a trunked system sound anything like this ?

no a trunked system will have analog voice channels or digital voice channels or both and a control channel, the analog voice will sound like normal voice, digital voice will sound usually like white noise/open squelch and the control channel will sound like an engine running, or in the case of an EDACS/MA-com control channel, a diesel engine

www.radioreference.com is a good site to search out you're local conventional frequencies and trunked radio systems in use in you're area.

mark

Originally Posted by Dave Flowerday

Many types of transmitters are required to transmit a Station Identification in Morse code by the FCC every so often. I work at Motorola on digital trunked radio systems and our systems have the capability to transmit a Morse code station ID in between digital transmissions to meet FCC requirements.

The audio clip you posted sounds like either a paging system or a trunked radio channel to me.

Motorola eh? If I buy a MotoTRBO radio is there any way I can use it to "receive only" like a scanner or does that TRBO system use a combination of 500,000 possible privacy codes? I know it's not encryption but I am under the understanding that it's a flavor of CDMA with some kind of code that is set by the end users when they set up the system.

It is becoming quite popular here in Ontario from some public services and even one fire dept so far.

Looks like Toronto and area is all going 700mhz P25 with probably encryption in a couple of years by the way which is terrible news for us who work in news

m

Originally Posted by Don Rotolo

OK, that all fits.

Go to the FCC page I quoted in Post 4, type in WPVQ32 and hit Search.
I chose WPVQ322 and found it is registered to Cook Telecom in San Francisco, authorized frequencies between 152.825 and 152.855 for service CP (Part 22 VHF/UHF Paging).

POCSAG is by far the most popular paging protocol, and the fact that you can decode ANY data proves that you have the right one - if it was something else you'd get nothing.

Speaking of POCSAG, we have some of that up here and there might be a couple of channels I should probably get serious about decoding

Now I have several scanners since I work in news but my only Computer is my laptop, Asus F3 series.

To properly decode do I need a desktop, sound card and source audio have to be from the discriminator tap on the scanner or can I actually grab it out of the headphone jack on the scanner and into the computer via the microphone input jack?

I'm not to sure about all this on a laptop, on a desktop I have read it's quite easy to do via the soundcard now.

thanks
m