The message I am responding to is 18 days old as I have gotten
a bit behind in reading this list so don't get too mad at me.
The Washington, D.C. Metro Police Department uses a digital
system that I assume may be an APCO25 system. The audio encoding and
decoding is Linear Predictive Coding or LPC and is kind of a
sophisticated technique in which a person's voice is analyzed and data
are sent as to frequency and wave form so that the decoder on the
other end can make noises that are pretty close to what went in to the
transmission end. When somebody gets out of range or there is
interference, some of the recipe for making the right noise is lost
and the receiver sort of sticks on the last sounds it got which makes
for some really weird sounds, kind of like "Star Wars." A person's
voice suddenly disappears in to a brief cacophony of beeps and bleeps.
Some people's voices come across perfectly while others sound
as if heard through water.
There is also a digital mode on the ham bands called D Star
which is based upon an open standard. I think Icom is the only
company making a D Star transceiver.
I think this is all exciting and I hope we eventually get lots
of D Star and APCO25 transceivers to use.
As for accessibility, there are two ways to skin this cat. I
bought a BC780 scanner almost 3 years ago but I hear that the Unidens
with a computer interface use a similar protocol and the protocol is
published.
I access mine via Linux and I also accessed it for awhile
under DOS and MSKermit in terminal mode.
If you think of doing this, be sure to be patient. Sometimes,
it is difficult to recon sile the commands you can give with the
instructions in the operator's manual which, by the way, is on the
Uniden web site.
I have gotten mine to track Motorola SmartZone systems in my
area, but I haven't had the need to try to follow some of the other
types of systems it will track such as the Johnson and Ericsson
trunked systems. Some how, listening to cement trucks make deliveries
in Oklahoma City which is about 50 Miles to the South is not a burning
desire. At least one of the 450-MHZ trunked systems I can hear from
here is operated by somebody who does a lot of Earth-moving for hire.
All our local emergency services are still on discrete
channels and use PL tones which also are manageable through the
BC780's command set.
The other question you need to answer if you want to use a
third-party program with your radio is whether or not it is
accessible. If you use JAWS, make sure the graphics don't kill your
attempts to do useful things with the program.
I hope this gives some food for thought and wasn't too drawn
out.
Season's greetings to all,
Martin McCormick WB5AGZ Stillwater, OK
OSU Information Technology Department Network Operations Group
Jeff Kenyon writes:
>Well, when an APCO-25 signal starts to faid it sounds more robotic, and
>then it faids out. I wish I had had my digital scanner on when I heard
>the modulation. Does anyone know how well the software for this system
>works with JFW? I have heard not too good of things about Motorola
>equipment, but what about the other vendors like Uniden and E.F. Johnson
>and the other P-25 radio manufacturers?
>
>
>
>
>
>On Fri, 2 Dec 2005, Dave Marthouse wrote:
>
>> As I understand it they are using apco25 just like any other amateur mode.
>> I don't have any data about range comparisons. I would be interested in
>> seeing how close to the noise floor an apco25 signal can go before it
>> becomes unintelligible.
>>
>> Dave Marthouse N2AAM
>> [log in to unmask]
>>
>>
>>
>>
>> ----- Original Message -----
>> From: "Jeff Kenyon" <[log in to unmask]>
>> To: <[log in to unmask]>
>> Sent: Friday, December 02, 2005 1:09 PM
>> Subject: Re: Project-25 digital modulation on the ham bands?
>>
>>
>> > What are they doing range testing or what? Any APCO-25 repeaters on the
>> > ham bands as of yet that anyon knows of?
>> >
>> >
>> >
>> >
>> >
>> > On Thu, 1 Dec 2005, Dave Marthouse wrote:
>> >
>> > > Jeff,
>> > >
>> > > There are groups of hams using apco25 in small pockets around the
>> country.
>> > > I know of a group in New Jersey as well as a few in Illinois, Texas and
>> > > Arizona. I'm sure that there are a few more scattered around the
>> nation.
>> > >
>> > > Dave Marthouse N2AAM
>> > > [log in to unmask]
>> > >
>> > >
>> > >
>> > > ----- Original Message -----
>> > > From: "Jeff Kenyon" <[log in to unmask]>
>> > > To: <[log in to unmask]>
>> > > Sent: Thursday, December 01, 2005 7:14 PM
>> > > Subject: Project-25 digital modulation on the ham bands?
>> > >
>> > >
>> > > > Hi everyone, I was just wondering if anyone has heard of anyone using
>> > > > APCO-25 Digital Modulation on the ham bands? On Tuesday I was looking
>> > > > around 2-meters and thought I heard a blip of data that sounded like
>> > > > Astro-25 digital data. I couldn't tell for sure as the signal was
>> weak,
>> > > > but wasn't using a digital scanner that I have, but just the THF6.
>> I'm
>> > > > just wondering if anyone else has heard anything like this?
>> > > >
>> > > >
>> > >
>> >
>> >
>>
>
|
