[ScanIndiana] (no subject)

Tue Jun 22 17:53:41 EDT 2004

Rob, you are correct about the 250/785 not working on a 9.6, 6.5 Khz C-QPSK
CC. However, where do you find this info that a system has to have a 9.6 bps
CC to be a "true" APCO Project 25 system? Here is a quote straight from the
P25 web site:

http://www.project25.org/display.php?file=content/WhatIs/compliance.htm
What is Required for P25 Compliance?
At a minimum, a P25 radio system must provide interoperability with these
two mandatory P25 Standard interface components:

·        The Common Air Interface (CAI)

·        The Improved Multi-Band Excitation (IMBE) vocoder

The CAI enables P25 radios to interoperate and communicate digitally across
P25 networks and directly.  This portion of the P25 standard suite was
selected to meet the unique radio system needs of the public safety
environment; coverage reliability, system design flexibility, and
inter-vendor compatibility.

The IMBE vocoder sets a uniform standard for converting speech into the
digital bitstream.  IMBE was selected as the coding scheme most successful
at making male and female voices audible against background noises such as
moving vehicles, sirens, gunshots, and traffic noise - the conditions of
public safety use.

These two components, when used together enable P25 users to interoperate
and communicate digitally directly between units and across networks,
agencies, and vendors.

P25 has also defined standard modes of operation to enable multi-vendor
interoperability for additional system functions: trunking, encryption,
over-the-air rekeying, to name a few.

Project 25 also continues to develop a set of defined system interfaces
allow the P25 system elements to communicate with host computers, data
terminals and the public switched telephone network (PSTN).  These
interfaces are critical to assure that P25 systems maintain compatibility
with the evolving telecommunications and data-communications world.

Now a quote from the APCO web site:
http://www.apcointl.org/frequency/project25/information.html
FEATURES OF APCO 25
6.25 kHz Bandwidth (CQPSK) Modulation- Or 9600 Baud

The CQPSK modulator consists of a table look-up, the two outputs of which (I
and Q) are Nyquist filtered and then amplitude modulated, in phase and
quadrature phase, before summing. The information bits are processed by the
look-up table to yield a 5-level I signal and a 5-level Q signal. The I and
Q signals are filtered with the Nyquist Raised Cosine Filter previously
described. The I signal is then multiplied by the carrier and the Q signal
is multiplied by the carrier after it has been delayed by 90 degrees. The
modulated I and Q carriers are then summed together to yield the modulator
output.

12.5kHz Bandwidth (C4FM) Modulation- Or 3600 Baud

The C4FM modulator consists of a Nyquist Raised Cosine Filter, cascaded with
a shaping filter, cascaded with a frequency modulator.

Flexible Modulation Method

A pair of modulation methods have been selected that utilize a common
receiver. The first, which utilizes a constant-envelope 4-level Frequency
Modulation (FM) variant, can utilize simple, high-efficiency amplifiers and
has emissions that fit within a 12.5 kHz bandwidth. This method will be
fielded in most equipment initially. The second, which utilizes a CQPSK
variant with amplitude components, requires the use of highly linear or
linearized amplifiers and has emissions that fit within a 6.25 kHz
bandwidth. (The receiver, common to both, has a 6.25 kHz bandwidth.)

Sounds like they are both APCO P25 to me........

Now, if you saying an ALL DIGITAL system has to have a 9.6 bps CC you are
correct. But I don't think one can say that a 3.6 bps system isn't an APCO
P25 system. As long as the digital meets the APCO Project 25 requirements it
is an APCO P25 compliant system, is it not? I don't think there is such a
thing as a "true" APCO 25 system. As long as the system complies with the
Project 25 requirements it's an APCO P25 system.

In short, the chances of MECA 1 going 9.6 bps is not likely as they need the
Analog for MECA2. I can't see them upgrading MECA 2 to digital, but who
knows maybe they will....

-Steve

----- Original Message ----- 
From: "Rob Dale" <rdale at skywatch.org>
To: "'Indiana Scanning'" <scanindiana at mailman.qth.net>
Sent: Tuesday, June 22, 2004 9:58 AM
Subject: RE: [ScanIndiana] (no subject)

> And it's quite clear people can be rude anywhere, which only serves to
make
> themselves look worse when they are wrong. I spend plenty of time chasing
> storms in Indiana so am fairly familiar with your systems.
>
> A true APCO25 digital system has a 9600 baud control channel, so if Indy
(or
> anyone else) moves to that upgrade route your BC250 / 785 scanners WILL
NOT
> WORK.
>
>  - Rob
>
> > -----Original Message-----
> > From: scanindiana-bounces at mailman.qth.net
> > [mailto:scanindiana-bounces at mailman.qth.net] On Behalf Of
> > Tim/Cindy Delong
> > Sent: Tuesday, June 22, 2004 12:01 AM
> > To: Indiana Scanning
> > Subject: Re: [ScanIndiana] (no subject)
> >
> > Steve, thanks for the backup and setting the record straight
> > for our friends in Michigan, we are in Indianapolis,Indiana
>
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