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Project 25 Technologies Discussion forum for the Project 25 Standard and its related technologies

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Old 05-05-2008, 10:48 AM
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Question Question for those smarted than me

It may be covered in another forum somewhere, could somebody explain how a project 25 digital trunking system works, (just the basics). My issue is that a county we regularly respond into currently uses VHF radios, our aircraft has vhf capability so we can talk no probelm. The county is planning on switching to a digital Project 25 trunking system in the near future. Will we be able to talk to then at all or are we going to need a new radio in the aircraft? Thank you for the help.

Jonathan Almand
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Old 05-05-2008, 11:08 AM
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Doesn't your state have a state interoperability plan? Maybe it would be worth checking
it out.

Anyway, there are national interoperability frequencies that are set aside by the FCC
for just this purpose. These frequencies are in the VHF, UHF and 800 MHz bands. I
know someone will come along and say there are channels in the 700 MHz band
also. I have stayed away from those channels as the dust hasn't settled on just
where when and how those will be implemented. Give it some time and the 700
channels will solidify and we all will know just what will go on there.

Back to the VHF band. There are 5 simplex channels that are for the use of
public safety agencies in the need for mutual aid / interoperability. These 5
channels are not to be used for daily traffic, but for incidents where multi
agency activity needs to allow them to communicate.

If you have these interop channels programmed into all your mobiles and portables,
you have solved 90% of your communications problems. The other 10% is going
to be a major hurdle. This can be considered a major hurdle as it is due to
the nasty word politics. If the chief's of the departments won't work together,
then the radio interop will never happen. You will end up having to go to "their"
frequency when you respond.

The down side of continuing to use the regular radio channels for the mutual aid,
is that it tends to clog up those channels for additional traffic. If you can move
the incident traffic to a different channel, this leaves the primary radio channels
available for additional calls.

Being that most mutual aid calls only have to cover a short distance of a block or
2, even the simplex operation at 800 Mhz works fine. Sure there are those that
say "We have to record all radio traffic". There are ways to do this, but that is
not the point of using the national interop channels. They provide a place for
a radio user to go. These channels are analog, so any radio you have today, be
it a P25, digital, Motorola, MA-COM, BK or what ever, they can all talk together
on these analog channels.

Starting to see the point of using the national interop channels. Bash it around
in your department. Talk to your mutual aid departments. It doesn't take a
rocket scientist to make it work. Just need to get the chief's so they will talk
to each other. Big point here is that just about all the states have these
frequencies used in their state interoperability documents. Contact your
state SIEC and get the details.

Jim




Quote:
Originally Posted by Umbro98765
It may be covered in another forum somewhere, could somebody explain how a project 25 digital trunking system works, (just the basics). My issue is that a county we regularly respond into currently uses VHF radios, our aircraft has vhf capability so we can talk no probelm. The county is planning on switching to a digital Project 25 trunking system in the near future. Will we be able to talk to then at all or are we going to need a new radio in the aircraft? Thank you for the help.

Jonathan Almand
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Jim
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Old 05-05-2008, 12:37 PM
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Thumbs up Thanks

Thanks, that helps
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Old 05-06-2008, 06:10 PM
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If they put in a new radio system the simple answer forget the mutual aid freqs. Get them to give you or buy a radio on the system.
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Old 05-17-2008, 07:01 PM
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Project 25 digital trunked radio systems -

1. use radios that transmit and receive digital radio signals (made up of ones and zeros)

2. trunking moves messages around on different channels - like when you go into a bank, and get into one line to access several different tellers

Thats P25 as short and sweet as I can make it. Peter Sz
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Old 05-17-2008, 08:24 PM
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See if they can set up in the console configuration a Base Interface Module (BIM) tied to a VHF radio on the frequency you interoperate with them on or your dedicated system. It can be set up as a console resource and patched to anything they have going on.

Other option is to buy some P25 radios on the system, but that can get expensive especially if the use is occassional.
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Old 05-24-2008, 02:38 PM
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It's possible (and not at all expensive) to patch a specific talkgroup from a trunked system into
any other radio system, like for example, a specific VHF repeater.

It can be done with voice-over-ip hardware, and controlled over ethernet via a local or internet connection, or it can be hardwired by connection the TX and RX audio lines from
a trunked radio to the conventional repeater. The trunked radio stays on the designated
interoperability talkgroup.


Elroy
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