[ScanIndiana] (no subject)

Tue Jun 22 20:09:23 EDT 2004

A system is only 100% APCO compliant if (among other things) it has a 9600
Baud control signal.  But nowhere is it written that a system has to be
100% compliant.  SAFE-T is a good example.  They could have made it a 100%
compliant system, but that would have eliminated ANY analog talkgroups,
and thus would have mandated that departments buy the more expensive
digital capable radios.  As it stands, departments like Deleware County
Sheriff's Department could migrate to SAFE-T without buying all new radios
for the officers.  They figured this was worth the trade of not having a
100% compliant system.

> 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
>>
>>    ____              ____        ___
>>   / __/______ ____  /  _/__  ___/ (_)__ ____  ___ _
>>  _\ \/ __/ _ `/ _ \_/ // _ \/ _  / / _ `/ _ \/ _ `/
>> /___/\__/\_,_/_//_/___/_//_/\_,_/_/\_,_/_//_/\_,_/
>>
>> ______________________________________________
>> ScanIndiana mailing list
>> ScanIndiana at mailman.qth.net
>> http://mailman.qth.net/mailman/listinfo/scanindiana
>>
>> Visit Indiana's source for Scanner Information!
>> http://www.indyscan.com
>
>    ____              ____        ___
>   / __/______ ____  /  _/__  ___/ (_)__ ____  ___ _
>  _\ \/ __/ _ `/ _ \_/ // _ \/ _  / / _ `/ _ \/ _ `/
> /___/\__/\_,_/_//_/___/_//_/\_,_/_/\_,_/_//_/\_,_/
>
> ______________________________________________
> ScanIndiana mailing list
> ScanIndiana at mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/scanindiana
>
> Visit Indiana's source for Scanner Information!  http://www.indyscan.com