Re: [Discuss-gnuradio] EDACS Control Channel

[Frank Brickle]

If you poke around the net, you will probably be able to find the source 
for an old DOS program that decodes EDACS control channel. It's called 
"Trunk Tracker."

I also have original source for an EDACS control channel decoder of my 
own from a number of years ago. Unfortunately all that remains is a 
hardcopy, but if you want, I can scan and provide that, probably.

Both of these assume that the demod and bitsync have been performed 
already and are being fed to their inputs as binary streams.

Frank

Ryan Pape wrote:
> Finally having all the pieces in place I need, I want to use the new
> GMSK code to decode an EDACS trunked radio control channel.
>
>
> Given my rudimentary knowledge on the topic (and gnuradio in general)
> which (if any) of the examples present would be my best starting point
> given that I'm hoping to do this, even initially, right off the air
> with the TV RX?
>
> Some details at
> http://users.netropolis.net/maverick/scanners/edacs.htm for anyone
> interested.
>
> Most relevant snippet for the uninitiated:
> ~~~~
>
> Modulation: It looks like GMSK (Gaussian Minimum Shift Keying) which
> is basically the same thing as two level FSK keying except that the
> data stream is passed through a low pass filter before modulating the
> carrier. This reduces the high frequency components allowing the
> control channel to fit within a 12.5KHz channel. Accordingly, a simple
> data-slicer circuit can be used to receive the control channel
> information.
>
> Baud Rate
>     9600 Baud
> Frame Sync
>     Frame synchronization is achieved by sending the following 48 bit sequence:
>     000101010101010101010111000100100101010101010101
>     or
>     0x155557125555 Hexadecimal
> Data Frames
>     After transmission of the frame synchronization sequence TWO data
> frames will be transmitted and then the whole cycle repeats ad
> infinitum. Each data frame is 120 bits long; this means 288 bits are
> transmitted in each cycle (2x120 bits for the data frames and 48 bits
> for frame sync).
>
>
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