VHF Trunking

[kyparamedic]

Many agencies go from VHF to an 800 MHz trunked system only to have a lot of coverage gaps that they didn't have before while operating on VHF. I know this is due to budgets and poor planning and not inherent of 800 MHz but why don't more VHF trunking systems exist? Sorry if this is a dumb question. Is it a technological reason or have to do with the FCC and frequency crowding? I'd think a 400 MHz trunked system would be a good compromise between the two but I'm no radio expert.

Thanks.

 

[N4DES]

Many agencies go from VHF to an 800 MHz trunked system only to have a lot of coverage gaps that they didn't have before while operating on VHF. I know this is due to budgets and poor planning and not inherent of 800 MHz but why don't more VHF trunking systems exist? Sorry if this is a dumb question. Is it a technological reason or have to do with the FCC and frequency crowding? I'd think a 400 MHz trunked system would be a good compromise between the two but I'm no radio expert.
Thanks.

Well one thing for sure, the utilization of trunking does zero to an agencies coverage footprint. It is the dramatic change of spectrum location that can affect it one way or the other.

We found an increase in talk-out coverage and in-bound reliability when we went from a VHF/UHF conventional single site transmitter configuration to a simulcast 800MHz configuration over our 2500 square mile county, but then again ours was engineered correctly and money wasn't an issue,

 

[boomboy64]

I know of at least one upcoming system on the east coast of Canada that is going from VHF to 700 MHz. This is going to raise the infrastructure costs as they have to go from 34 sites to 80+, but trying to implement a trunking system in VHF just wasn't possible due to the VHF congestion coming up from the US seaboard. They could actually do it with their current allocated VHF frequencies, but it would've had no chance of getting extras for any future expansion.

 

[studgeman]

Well you pretty much have it figured out. Coordination wise, except for certain circumstances VHF is pretty much fair game for any users. There is also no band plan where inputs and outputs are sperated by x amount of distance, (5 meg UHF, 3 Meg T-Band, 45 Meg 800) propagation is better over longer distances, VHF narrow-band still has adjacent channel overlap problems. Essentially this all adds up to a very difficult time obtaining VHF spectrum for trunking. Ironically some of the same problems that make VHF hard to trunk on at a local level, make it desirable at a state level, adding to that certain frequencies are for state police licenses ONLY, so it can sometimes be eaiser on a statewide basis.

UHF doenst have the same extent of coordination issues, and doesnt suffer from adjacent channel overlap, Many counties in New York State are implimenting UHF trunking systems, you will have to examine frequency availability for your region.

There is no technolgical limitation to trunking in any frequency band, trunking protocols are essentially frequency agnostic, the limits are hardware (does someone make a radio?) and regulatory.

You are right in your assumption about frequency vs coverage. UHF is generally a good compromise, and is praticularily effective in urban areas. UHF also more easily gets into and out of masonary/steel buildings. As with any radio system design, it all comes down to design, a poorly designed system will operate poorly.

 

[Grog]

I want to see a trunked system on 42mhz

 

[citylink_uk]

We have several MPT1327 systems here in the UK which operate on 82 to 87mhz.

 

[a1emt]

Washington County, WI is currently in the planning stages of a VHF P25 Simulcast Trunking system (to be built by M/A-Com). They are still putting together all of their frequencies, as another post mentioned there are no pre-set input / output frequencies in VHF. The State of WI is also in the planning stages of a Statewide VHF P25 Trunked System.

Jim

 

[RLADY22]

Trunking..frequencies

Trunking was origionally started as a way to provide several different "groups or companies" a way to "talk privately" on frequencies (in the begining it was usually five or so, and with in these five were usually -depending on manufacturers with in these five frequencies there were additional codes -each could be a separate "talk group"-por prvate conversation group)So these five frequencies could actually accomidate several different private groups(five frequencies times how many ever codes per repeater)even though the frequencies (repeaters) were really being used by several other people, only those with the same identical repeater and code would hear themselves..no eavesdropping, little to no busies etc....much like moving from prty line phones to the "trunked"telephone systems of today. With trunked radio multiple conversations took place at the same time without people on the same repeaters(or system) hearing the conversation..or not being able to talk..trunking was hard to scan because conversations that might have started on repeater one talk group 18 might after a transmission "move"to amother repeater within the trunk to accomodate other traffic, so the more users on a system the harder to scan or listen in on a conversation...computers became a larger part of radio technology ans spectrum usage...some manufactures..would use a computer on the first repeater...while others used computers on all repeaters..which in my opinion was best for users in that losing one repeater didnt mean the whole system went down..now aas with digital anything it is clearer..however fringe or staticy receptions are competely dropped..which may seem like insignificant until you are in upstate New York with loads of trees and hills and you cant communicate at all because your on the fringe...

Frequencies..the lower the frequency the farther it goes, the less predictable it is..today you might hear syracuse only..then suddenly because of changes in weather etc.(leaves on trees) you might hear California smog control(actually happened long before I was in the business)As you progress up the scale the higher the frequency the more repeaters or towers you need to cover an area(ever notice the number of cell towers needed to cover an area).Manufacturers and the fcc wag this business and the migration of trunking 800(900?in cities),vhf..uhf..never in my opinion was as planned as one would think(nextel is another betime story you might like)and truth be told the layout of the land..and local dealers could save a lot of heartache..what talks in Florida on eight sites would probable need five times that many in upstate new york...well night night..hope I didnt confuse you more than help...

 

[RadioGuy7268]

Short answer - VHF trunking rocks once it's up & working.

Much longer answer - it's darn near impossible in any metro area to get enough clear channels to build a VHF system with more than a few channels and more than 2 or 3 site locations. VHF works well for high powered mobiles, but portable range is lacking, especially for in-building coverage and talk-back. VHF would work much better if you can get some paired frequencies, and also get exclusivity.

You need experienced help to set up a proper VHF trunking system. Even someone who has done a UHF LTR system with success is going to have a learning curve when it comes to VHF. Find an old radio guy who lived & breathed VHF..... you'll find a fountain of knowledge about cavities, piezo filters, propogation, and antennas.

 

[RLADY22]

Short answer - VHF trunking rocks once it's up & working.

Much longer answer - it's darn near impossible in any metro area to get enough clear channels to build a VHF system with more than a few channels and more than 2 or 3 site locations. VHF works well for high powered mobiles, but portable range is lacking, especially for in-building coverage and talk-back. VHF would work much better if you can get some paired frequencies, and also get exclusivity.

You need experienced help to set up a proper VHF trunking system. Even someone who has done a UHF LTR system with success is going to have a learning curve when it comes to VHF. Find an old radio guy who lived & breathed VHF..... you'll find a fountain of knowledge about cavities, piezo filters, propogation, and antennas.

Yes us old geezers..do have info.. you need to find one that is not interested in telling you specifically what to do..but to have someone willing to tell you their stories...and then look to other geezers for additional stories. Preferably people who arent consultants or have...no monetarily or political reasons to "provide information"... kick the tires its usually free...then talk to those who "are special consultants" etc...with the knowledge that the "homework"you have done has taken years of trial and error...and is a foundation for todays technologies...Good Luck

 

[zerg901]

Alaska, North Dakota, and South Dakota have statewide VHF TRS. Virginia, Montana, Wyoming, and Nebraska are building their VHF TRS. Wisconsin apparently has a VHF TRS on the drawing board. (That info might not be 100% accurate - but I know for a fact that Montana and Wyoming have licensed multiple VHF trunked sites in 2008.) I think that Nevada had a VHF TRS until they "realized" that it was not licensed by the FCC.

West Virginia is adding more UHF TRS sites this year.

Peter Sz