Need help getting Broome County's new P25 to work with SDS200

GTR8000

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All radios are now natively in the UHF band. The trunked system, well more specifically the two Broome County Simulcast cells, also operate natively in the UHF band. Those two Broome County cells are part of a larger system that covers multiple counties in the region, however each county has their own slice of bandwidth and unique frequencies, all of which are controlled by a single master controller (system core). Trunked systems are 80% computers and 20% RF these days.

That's the simple overview of how it works. There are many more details of how P25 systems actually work that you can find online if you wish to research it, but I'll explain a bit more here just for kicks.

A trunked "site" is a physical location where the transmitters (repeaters), antennas, and all the other associated hardware lives. Not all that different from a low band base station 50 years ago, the purpose is to receive and transmit RF signals. A trunked system combines multiple frequencies into a pool that is shared by all users of the system, no one frequency is exclusive to any purpose anymore. Instead the master system controller assigns frequencies seemingly at random as they are needed by radios that want to talk to each other. This maximizes efficiency, as you no longer require many discreet frequencies assigned for a single purpose, so for example you don't have an "OEM" channel with a frequency all to itself that is idle 95% of the year, which is a waste of valuable spectrum.

In the case of Broome County, and other similar trunked systems, there are multiple physical "sites" that are combined to form a cell, or a collection of sites. When combined like that, each of those physical sites is known as a "subsite", and the collection of subsites forms a simulcast cell. Simulcast because each subsite is simultaneously receiving and transmitting on the same set of frequencies to provide wide area coverage without requiring a ridiculous amount of individual unique frequencies. So instead you maybe have 10 of these subsites sharing the same 6 frequencies, as is the case with the Broome County West cell. No matter where you are within the coverage area of those 10 subsites, all of the radios (called "subscribers") are receiving and transmitting on the same pool of 6 frequencies., which dramatically improves the breadth of coverage without having to actually change over to another frequency/repeater/channel manually. The system takes care of it all for you. And if you were to drive from the western half of the county into the eastern half, then the subscriber will "roam" to the East cell and you would continue to operate seamlessly.

So in addition to the collection of frequencies that make up a trunked site or simulcast cell, you also have "talkgroups" which are the virtual "channels" that the radios/subscriber operate on. As noted earlier, no one frequency is dedicated to any particular talkgroup, instead they just rotate around the pool of available channels in a first come/first serve manner. So one transmission on the Sheriff's Dispatch talkgroup of 27210 might take place on 454.475, and a few seconds later another transmission on the same talkgroup might take place on 453.425. The system tells all of the radios on that talkgroup which frequency to tune to, it all happens in the blink of an eye.

There's a lot more to it, but that should be enough of a primer to get you some basic understand. Oh and PS it's trunking, not "trucking".
 

DmxDesigner

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Feb 26, 2012
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9
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Binghamton, N.Y.
All radios are now natively in the UHF band. The trunked system, well more specifically the two Broome County Simulcast cells, also operate natively in the UHF band. Those two Broome County cells are part of a larger system that covers multiple counties in the region, however each county has their own slice of bandwidth and unique frequencies, all of which are controlled by a single master controller (system core). Trunked systems are 80% computers and 20% RF these days.

That's the simple overview of how it works. There are many more details of how P25 systems actually work that you can find online if you wish to research it, but I'll explain a bit more here just for kicks.

A trunked "site" is a physical location where the transmitters (repeaters), antennas, and all the other associated hardware lives. Not all that different from a low band base station 50 years ago, the purpose is to receive and transmit RF signals. A trunked system combines multiple frequencies into a pool that is shared by all users of the system, no one frequency is exclusive to any purpose anymore. Instead the master system controller assigns frequencies seemingly at random as they are needed by radios that want to talk to each other. This maximizes efficiency, as you no longer require many discreet frequencies assigned for a single purpose, so for example you don't have an "OEM" channel with a frequency all to itself that is idle 95% of the year, which is a waste of valuable spectrum.

In the case of Broome County, and other similar trunked systems, there are multiple physical "sites" that are combined to form a cell, or a collection of sites. When combined like that, each of those physical sites is known as a "subsite", and the collection of subsites forms a simulcast cell. Simulcast because each subsite is simultaneously receiving and transmitting on the same set of frequencies to provide wide area coverage without requiring a ridiculous amount of individual unique frequencies. So instead you maybe have 10 of these subsites sharing the same 6 frequencies, as is the case with the Broome County West cell. No matter where you are within the coverage area of those 10 subsites, all of the radios (called "subscribers") are receiving and transmitting on the same pool of 6 frequencies., which dramatically improves the breadth of coverage without having to actually change over to another frequency/repeater/channel manually. The system takes care of it all for you. And if you were to drive from the western half of the county into the eastern half, then the subscriber will "roam" to the East cell and you would continue to operate seamlessly.

So in addition to the collection of frequencies that make up a trunked site or simulcast cell, you also have "talkgroups" which are the virtual "channels" that the radios/subscriber operate on. As noted earlier, no one frequency is dedicated to any particular talkgroup, instead they just rotate around the pool of available channels in a first come/first serve manner. So one transmission on the Sheriff's Dispatch talkgroup of 27210 might take place on 454.475, and a few seconds later another transmission on the same talkgroup might take place on 453.425. The system tells all of the radios on that talkgroup which frequency to tune to, it all happens in the blink of an eye.

There's a lot more to it, but that should be enough of a primer to get you some basic understand. Oh and PS it's trunking, not "trucking".
Thanks so much for this info. It's amazing how technology and of course the computers that manage all this so efficiently. Thank you for taking the time to explain the basics of this. It now makes sense to my understanding.
 

k2hz

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Feb 7, 2011
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Rochester, NY
I just revisited the P25 system and I'm very impressed so far. I have a question without getting too deep into the specifics... Are all the agencies now in the 450 mhz band, split between the assigned tower frequencies in that band via talkgroups? Or do the 450 mhz frequencies link to control the previous conventional talk frequencies. Ie: Our old country wide fire frequency 33.9 mhz was the channel we all used back in the 70's when I was a volunteer fire fighter. I realize the previous updated F.D. dispatch is up around 150 mhz, and a drop back to 33.9 is still used but rarely. I'm trying to wrap my head around what changed as per specific radios in trucks, and fire depts.. with this new network. Are all the new radios now up in the 450 mhz band? I'll try to find more tutorals on what exactly is a P25 trucked network. Thanks to anyone who can shed some insight on this for me.
See this thread for the latest info on the system:
Low Band and most VHF is dead except for links to the P25 system dispatch. New UHF conventional channels are used for tactical, on-site, operations to supplement the P25 trunked talk groups which will be where most communications will occur.
 

bcrmc

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Feb 1, 2018
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44
Location
NY
I just revisited the P25 system and I'm very impressed so far. I have a question without getting too deep into the specifics... Are all the agencies now in the 450 mhz band, split between the assigned tower frequencies in that band via talkgroups? Or do the 450 mhz frequencies link to control the previous conventional talk frequencies. Ie: Our old country wide fire frequency 33.9 mhz was the channel we all used back in the 70's when I was a volunteer fire fighter. I realize the previous updated F.D. dispatch is up around 150 mhz, and a drop back to 33.9 is still used but rarely. I'm trying to wrap my head around what changed as per specific radios in trucks, and fire depts.. with this new network. Are all the new radios now up in the 450 mhz band? I'll try to find more tutorals on what exactly is a P25 trucked network. Thanks to anyone who can shed some insight on this for me.
All agencies in Broome County are now operating on the Central NY Interoperable Communications Consortium, P25 radio system. The trunked, simulcast system uses several frequencies from 453.xxxx MHz through 465.xxxx MHz. In addition to having talk groups on the trunked system they also have some simplex UHF channels used for localized on-scene operations. All are digital P25. There are no Fire, EMS, Law Enforcement, or Public Works left in Broome County using VHF low or VHF high frequencies with the exception of NY State DOT and NY State Police. The state police are using the P25 system but they are also simulcasting on their legacy VHF high channels. More information can be found here: Central New York Interoperable Communications Consortium (CNYICC) Trunking System, Regional, New York
 

bcrmc

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NY
See this thread for the latest info on the system:
Low Band and most VHF is dead except for links to the P25 system dispatch. New UHF conventional channels are used for tactical, on-site, operations to supplement the P25 trunked talk groups which will be where most communications will occur.
I failed to mention that Broome County still uses low band 45.88 (LFIRE4D) for interop communication with surrounding NY Counties.
 
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