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RE: [Discuss-gnuradio] PMR data decode

From: Johnathan Corgan
Subject: RE: [Discuss-gnuradio] PMR data decode
Date: 08 Jul 2002 18:39:52 -0700

On Mon, 2002-07-08 at 15:17, Ettus, Matt wrote:

> ok.  so this got me interested in pagers.  I'm not that up to date on the
> technology used today.  For your standard one-way pagers, what frequencies,
> speeds, and specs are used in the US?  A quick web search found POCSAG, APOC
> phase 1, and Golay (from motorola).  POCSAG seems to come in many speeds.

POCSAG is popular but is mostly a legacy system. Practically all new
pager installations are using the Motorola FLEX protocol.  The primary
FCC allocation for this is in the 929-931 and 940-941 Mhz bands.

FLEX uses an FSK or 4FSK modulated signal at either 1600 or 3200 baud
for a total of four different data rates.  Data is interleaved and
BCH(32,11) encoded as well.

While the frame format and protocol is well documented by Motorola, the
preamble data sequences which indicate the immediately following frame
format are considered proprietary trade secret information.  It IS
available on the Internet if you search for it, but since it isn't
documented as legally reverse engineered, it is questionable whether you
can distribute it in the US jurisdiction.

Reverse engineering the sync codes via on-air transmissions is quite
easy; however, in the US the Electronic Communications Privacy Act of
1986 makes even the monitoring of these signals questionably legal.

-Johnathan, KG6KWT

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