Why use Simulcast in a trunked system ??

[BamaScan]

I found a frequency tonight that I never would. I live to far to hear the 800 mhz frequency. The vhf frequency comes in strong at night. It is the Fire Dispatch channel for Tallahassee, FL Fire. The City of Tallahassee is 800 mhz and trunked. The Fire frequency is on 800 mhz as well as vhf.
My question is why is Simulcast used on the Fire Frequency ? Is this so other fire departments could talk to Tallassee Fire on vhf ? If this is the case why not simulcast the Police or Sheriff as well ?

 

[swstow]

for vol fire that cant afford trunking scanners

not really, nox (sp) boxs cant be opened with a 800 radio for some reason the tone only works on the lower bands, well that is what i was told by a fire fighter friend

 

[ILMRadioMan]

I know many places use it for paging.

Minitor IV and V pagers in the VHF band. The dispatcher can page volunteers out, then send out the audio so they can be heard on the pages, then the VFD can respond on 800.

 

[WA4MJF]

I'm told that you can't page on the Moto Type II system. We have a VHF voice pager and a VHF alpha numeric pager to have the two ways of notifying the Fire personnel that the NC DOI requires.

 

[ILMRadioMan]

Well, its not the TRS thats paging.

Centracom dispatch systems (using CEBs) allow the control of multiple radio resources.

Here in Wilmington, NC, when Fire or EMS keys up to talk, they are actually keying on 4 different resources.

2 Type II motorola systems
1 P25 motorola system
VHF Transmitter

All 4 send out the same audio, however this is their sequence:

Using the dispatch console, they send out two tone paging signals over the VHF side...now they can be heard on all 3 TRS, but it does nothing besides audio.

So those tones activate the VHF pagers. Specifically the FD, which on the county side is a volunteer department, the volunteers dont all have their own individual radios on any of the TRS, however they do have pagers.

So the VHF pagers activates, and they hear the dispatch call go out over their VHF pagers.

Now all the while, all this audio is being sent out the 3 TRS as well. Once the volunteer reaches the scene, his station, etc...he gets on one of the TRS (likely the P25) and then all the traffic goes over TRS.

So the VHF is basically in simplex use for paging and the initial dispatch call, then all the traffic after the initial dispatch is done over the TRS.


I hope you follow along

 

[w8jjr]

It is also used when migrating from one system to another and havent completed the install and testing of all radios. This way they have a backup if there is a problem in the new system or all radios havent been installed yet.

 

[ILMRadioMan]

Oh and BTW, just to add, we have a fun way down here of "kind of " paging over TRS.

You can do call alert and the "page" function on many Type 2 TRS.


What we do down here to "page" on the TRS:

On newer mobiles they have a "VIP Out 1, 2 & 3" pins on the accessory connector.

These can act as a switched ground.

What we do is have the ID programmed into dispatch as a "call alert"

We have the sleeping room lights and speakers hooked up through relays.

At night, the lights are off, and there is no audio on the overhead speakers.


We have the B+ 13v output from the accessory connector to one side of the relay and the VIP on the other side of the relay.

When dispatch "pages" them, they are actually call alerting the ID of the radio. This then switches on the ground which flips the relay.

This then completes the circuit for the speaker output, and also turns on a light timer.

So essentially when the radio is call alerted, it turns the lights and speakers on, which obviously in turn wakes up the person and they recieve the dispatch.

 

[k8ble]

hello all
i ve been programing scanners for many years, but since 03 and the apco 25 sys came out the whole world has changed. i have both scanners 796/996 and they too are a world apart. what i have been having trouble with is trying to do a reset on the 796d, but found there no such operation, the real question is all my apco systems work but one, they all have the same settings but i can't hear a thing
on the other, also now the SQL has been oscillating up/down. the last question is .. on simulcast systems. for my metro area there are 4 simulcast sytems, with maybe 3-4 control channels do i need
to still add all the other freq's in the system?