VHF TRS options

[kcfm6]

What options, system types, are available for VHF trunking ? I work for an agency which has several paired VHF repeater frequencies and thought there might be a way to combine and trunk them.

Any thoughts or ideas ?

 

[N4DES]

Your first step would be to check with a frequency coordinator to check to see if you can trunk them. THe FCC has specific requirements for trunking under 512MHz. that must be adhered to....

http://a257.g.akamaitech.net/7/257/2422/13nov20061500/edocket.access.gpo.gov/cfr_2006/octqtr/47cfr90.187.htm

 

[studgeman]

Well the one trunking technology that gets around the cooridnation requirements is LTR, when programmed correctly. Other trunking technologies which require a dedicated control channel, EDACS, MPT-1327, P25, etc. require special coordination on any frequency below 512. The coordination mostly has to do with exclusive use provisions, since the control channel is active constantly and the system will assign a channel reguarless of wether it is in use by another co-channel licensee. Trunking below 512 is not impossible, but requies jumping through a few extra hoops.

If you are a public safety agency you may want to check with your regional National Law Enforcement Corrections Technology Center http://www.justnet.org they can give you a quick sanity check on the possibility of trunking those frequencies. The NLECTC centers are a free service funded by the National Institutes of Justice.

On a second note, I NEVER recommend LTR or similar technologies for public safety applications. The simple reason is the lack of rude preemption. Public Safety requires channel access when the emergency button is pressed. LTR does not handle emergency notifications, or allow for any type of rude preemption.

 

[kcfm6]

Thank you for all the info. I was unaware of the rude pre-emption issue and will contact our frequency coordinator. I will have to check out the referenced link, it sounds like they might have some interesting tips.

 

[studgeman]

yeah if you dont see anything that quite has what you are looking for, dont hesitate to call them. Its your tax dollars at work, might as well get some use outta them. btw, if you dont mind, what state are you in?

 

[kcfm6]

I am located in Knoxville, TN.

 

[RadioGuy7268]

VHF trunking with LTR is a pretty good setup. There's a few sites up across the country. MRT magazine did a write up a while back on a guy who has a setup in Texas - http://mrtmag.com/mag/radio_making_vhf_trunking/index.html

I agree with the other posters, you have to watch the way you set things up, but once you can get a clear open channel set up as your main "home" channel, you can do some pretty good things.

Tips - use Crystal filters on the receive side. Make sure the mobile transmit frequencies are as clean and clear as possible, and make sure you license them as FB8 so you don't end up with other co-channel or adjacent users. Do all you can to protect the receive side of the repeaters, and you'll have good performance.

I'd think you can get some nice clear freq's still in Knoxville. Good luck

 

[N_Jay]

If you have not already narrow-banded, it is a good time to look at upgrading your radio system beyond just adding trunking.

There are a number of good consultants that can help you through the process.

 

[ChooChooCharlie]

The only narrowband VHF trunking system in operation right now is Cecil County Maryland. You may want to look them up. I believe they are running EDACS. I saw on Incident Broadcast Network, they have a webpage www.ccdes.org.

 

[902]

The only narrowband VHF trunking system in operation right now is Cecil County Maryland. You may want to look them up. I believe they are running EDACS. I saw on Incident Broadcast Network, they have a webpage www.ccdes.org.

The trunked VHF P25 systems in the north central US are narrowband (1 voice path in a 12.5 kHz channelspace).

 

[902]

What options, system types, are available for VHF trunking ? I work for an agency which has several paired VHF repeater frequencies and thought there might be a way to combine and trunk them.

Any thoughts or ideas ?

If you are the person responsible for making this decision, I strongly suggest you contact "J.J." (John Johnson) to discuss the matter.

As others have stated, there are a number of complexities involved in trunking below 512 MHz. It is incumbent upon your agency to protect co-channel and adjacent channel operations from interference. As you can't control emissions by monitoring any longer, the only protection is to either design the system where it does not affect others, or to get their written permission stating they don't care if they get potential interference. This may mean reaching out and getting letters of concurrence from your co-channel and adjacent channel neighbors. From personal experience, I do my own engineering studies and will not issue an LOC for the systems I'm responsible for unless there is NO possibility of interference.

If you narrowband during the transition, two things will happen - your adjacents change from 15 kHz to 7.5 kHz (your real-world interference may remain until all systems are narrowbanded, and, since each VHF channel impinges on the next adjacent, possibly even afterwards) and your usable range will be truncated, necessitating some means of range recovery. Many choose to implement P25 as a range recovery mechanism. Your system may also become "right-sized" during the process. By right-sized, I mean subjected to Safe Harbor ERP limitations and other restrictions that may require you to have lower sites with lower ERP in simulcast configuration.

In other words, it may be very elaborate. As much as most of the advice you'll get here is valid, we are anonymous and have no obligation to be correct. John should be able to provide you with facts and guidance.