Re: [Discuss-gnuradio] EDACS Control Channel

[Ryan Pape]

I am comforatable with my prospects once I have that bit stream...it
is plugging the pieces together  to get to that point that I am having
trouble with.

On 4/15/06, Frank Brickle <address@hidden> wrote:
> 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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> > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >
> >
>
>