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380 mhz DOD Astro systems

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Mattsenft

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I was trying to gather some information on the Naval Support and Carlisle Barracks Astro systems in Mechanicsburg. I found three control channels but was unable to get Unitrunker to decode any of them. I tested the operation of my setup by decoding the Carlisle Borough and Lower Allen Type II systems. I tried inversion both ways but didn't have any luck. I will try to post wav recordings of the control channel for everyone to listen to. Thanks for any help in advance.
 

SCPD

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Hi Matt;

Some radios change polarity when switched from one band to another (like moving from 800 Mhz to 380 Mhz) - obviously you've covered that.

Get a software oscilloscope program - there are literally a dozen or so available. Use the program to get a picture of your signal as the computer sees it. If you're not sure what a good P25 signal looks like, post a picture here.

If the signal is straight from the radio's discriminator tap, consider building or buying a small buffer amplifier. One of those microphone pre-amp kits will work.

-rick
 

ka3jjz

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Is it possible that the sigs you got are 9600 baud encrypted CCs? That is supposedly the standard these new systems are supposed to be using - I doubt UniTrunker - or any other software - could handle that. Not all of them are, tho - one up here near Ft.Meade is not encrypted, but the one at NSA is.

The other obvious question - you can't feed the signal from your speaker output to the soundcard. A discriminator tap is required. 73s Mike
 

Mattsenft

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To answer your questions the control channel does not appear to be encrypted. I entered one of the control channels along with a nominal base and spacing frequency and some of the P25 voice channels into my 996T which seems to partially track it. I am using a tapped 796D and a pro-2055 for Unitrunker. The next time I get a chance to capture a waveform I will post it.
 
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