LSM simulcast audio sample from OP25

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KA1RBI

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Here is a WAV file that was captured from the Ontario simulcast system, which is located approx. 50 miles from here ("here" = ZIP code 13045).

The antenna was an indoor directional antenna and the receiver is a modified RS PRO-2006 mfg'd circa 1991. The SDR software is from the OP25 research project. OP25 is Free Software.

The system is Monroe and Ontario Counties Public Safety Trunking System, Regional, New York - Scanner Frequencies

The audio file is at http://www.lightlink.com/mhp/audio-out.wav - it's approx. 1.2MB in size.

Note there's a time-lapse effect - pauses are not present, due to the way the WAV file is generated...

Also it's interesting to note that a RS PRO-106 if connected to the same antenna doesn't even decode the control channel well enough to display the error percentage value, let alone to track voice channels.

73

Max
 

KA1RBI

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Portage Escarpment
Sounds awesome Max! This is using the CQPSK demodulator you wrote, correct?
Thanks Joe - yes, almost correct. I started off with the pre-existing GNU Radio mpsk_receiver_cc block, which I've been enhancing [hacking] off and on over the course of the last few years. The two biggest changes were to make PI/4 DQPSK work properly and to get rid of the Muller-Mueller and replace it with a Gardner clock recovery algo. It's still basically using the Costas loop, more or less... But I certainly didn't write the whole demodulator!

Also I've gotten feedback about the squeal / screech at the end of some of the transmissions - sounds like a bug, but it only happens after the end of the speech interval. It sounds like there are a few other artifacts as well, but they sound to me more like the MBE speech vocoder issues than modem problems...

73

Max
 

jcardani

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Orlando, FL & Ocean City, NJ
Hi Max,

I was just thinking. You guys should support DVSI's USB3000 P25 Dongle if possible. That should eliminate the MBE issues :) I believe Eric C. already has experience interfacing it with his version of DSD.

The only caveat is that the drivers are for Windows. Can OP25 and GNUradio work in Windows?

Edit: The OEM version of the USB3000 P25 dongle uses the FTDI drivers, which do support Linux and other OS.

Joe


Also I've gotten feedback about the squeal / screech at the end of some of the transmissions - sounds like a bug, but it only happens after the end of the speech interval. It sounds like there are a few other artifacts as well, but they sound to me more like the MBE speech vocoder issues than modem problems...

73

Max
 
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