[Discuss-gnuradio] EDACS Control Channel

[Ryan Pape]

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).