Trunking system inputs?

[Pr999]

Does anyone know how the inputs for trunked repeaters work? Because I really struggle with this. So this will be a pretty loaded question but I'll ask anyway.

1. Input Frequencies - Setup
When setting up a system for the first time, is there a ratio to how many outputs = input frequencies? also, how are these inputted transmissions tracked and put into their respective talkgroups?

2. Duplexing
Considering all repeaters need to be duplexed, how can one repeater repeat more than one channel? Do you need multiple duplexers or will just one do?

3. Licensing (non-700/800/900mhz)
How can I get licensed for this, not in the 700-900 MHz spectrum? will I have to get each frequency individual licensed?

Sorry if some of the questions seem stupid or misleading, I'm trying my best to ask questions like these correctly.

These questions aren't just for me though, they are so anyone who also stumbles upon this when wanting to know this type of stuff whether just by search or reference.

Thank you!

 

[KevinC]

Does anyone know how the inputs for trunked repeaters work? Because I really struggle with this. So this will be a pretty loaded question but I'll ask anyway.

1. Input Frequencies - Setup
When setting up a system for the first time, is there a ratio to how many outputs = input frequencies? also, how are these inputted transmissions tracked and put into their respective talkgroups?

2. Duplexing
Considering all repeaters need to be duplexed, how can one repeater repeat more than one channel? Do you need multiple duplexers or will just one do?

3. Licensing (non-700/800/900mhz)
How can I get licensed for this, not in the 700-900 MHz spectrum? will I have to get each frequency individual licensed?

Sorry if some of the questions seem stupid or misleading, I'm trying my best to ask questions like these correctly.

These questions aren't just for me though, they are so anyone who also stumbles upon this when wanting to know this type of stuff whether just by search or reference.

Thank you!

I may be a little odd, but I always shoot for the same number of inputs that I have outputs. It makes the repeaters work much better that way.

 

[mmckenna]

Does anyone know how the inputs for trunked repeaters work? Because I really struggle with this. So this will be a pretty loaded question but I'll ask anyway.

1. Input Frequencies - Setup
When setting up a system for the first time, is there a ratio to how many outputs = input frequencies? also, how are these inputted transmissions tracked and put into their respective talkgroups?

The frequencies are paired. One input frequency and one output frequency each pair. Ratio is 1:1 for TX:RX
When designing the system, they'll look at the number of users and can figure out how many talk paths are needed. Depending on the type of system, (FDMA vs. TDMA), it's some maths used to figure the amount of paths you need.

2. Duplexing
Considering all repeaters need to be duplexed, how can one repeater repeat more than one channel? Do you need multiple duplexers or will just one do?

On multichannel systems, they use a transmit combiner feeding a transmit antenna, and a receive multicoupler that used one RX antenna to feed all the receivers.

3. Licensing (non-700/800/900mhz)
How can I get licensed for this, not in the 700-900 MHz spectrum? will I have to get each frequency individual licensed?

You work through a frequency coordinator. The frequency coordinator will work with you to figure out how many pairs you need. They'll find suitable frequencies and help you file for the FCC license. Multiple frequencies can be licensed under one call sign.

 

[Pr999]

Here's another question: how does dual or triple band multi-site trunking work on single band radios?

 

[GTR8000]

Here's another question: how does dual or triple band multi-site trunking work on single band radios?

Well, it doesn't, because the single band radio is only aware of the band it's capable of. So it can only operate on infrastructure that matches whatever band it's capable of.

 

[kayn1n32008]

Here's another question: how does dual or triple band multi-site trunking work on single band radios?

If you have a single band radio, it will only use in band sites. Keep in mind that although 700 amd 800MHz are separate bands, they are treated as one band by most modern radios. Example, a 'U' split APX6000 single band portable will cover both 700MHz and 800MHz LMR bands.

I live in Alberta, and our province wide Harris trunk system uses 700MHz for the majority of the systems sites, but in western Alberta, there are a bunch of VHF sites in the mountains due to propagation/terrain and a lack of grid power to VERY isolated mountain top sites. If you are using a multiband radio that is configured to use the VHF sites, it will roam seamlessly to them from a 700MHz site, and back. If you are only capable of using 700MHz sites, it won't even know there are VHF sites.

 

[Pr999]

Well, it doesn't, because the single band radio is only aware of the band it's capable of. So it can only operate on infrastructure that matches whatever band it's capable of.

The reason I mention it in this way is that when I look at a lot of P25 and Motorola systems, depending on state and terrain, I see half of them are on a completely different band. It could be any of the combinations; VHF/UHF, VHF/700-800-900, UHF/700-800-900, VHF/UHF/700-800-900. So I just wonder how the radios stay on these systems while they roam. One thing I forgot to mention is that most departments use single-band radios, so it makes me curious when they need to travel around the state or to another region (namely DNR, State Police, and Fire.) This also applies to California's low band system, like how do they attach to a trunking system, if not at all.

 

[kayn1n32008]

The reason I mention it in this way is that when I look at a lot of P25 and Motorola systems, depending on state and terrain, I see half of them are on a completely different band. It could be any of the combinations; VHF/UHF, VHF/700-800-900, UHF/700-800-900, VHF/UHF/700-800-900. So I just wonder how the radios stay on these systems while they roam.

Well I doubt there are any muktiband public safety systems running on 900MHz, but to be using multiple bands, you need a multiband radio. Lots exist these days.

Each site has a control channel, and the controller sends out a neighbor lots, with channel numbers to the subscribers.

The subscriber radios have a preset signal strength roaming threshold. When the signal strength falls below that threshold, it will scan the neighbor list for the strongest neighbor, and then roam to that site, register, and affiliate to its selected talkgroup.

 

[Pr999]

Well I doubt there are any muktiband public safety systems running on 900MHz, but to be using multiple bands, you need a multiband radio. Lots exist these days.

Each site has a control channel, and the controller sends out a neighbor lots, with channel numbers to the subscribers.

The subscriber radios have a preset signal strength roaming threshold. When the signal strength falls below that threshold, it will scan the neighbor list for the strongest neighbor, and then roam to that site, register, and affiliate to its selected talkgroup.

And how does the radio's input get affected by this?

 

[kayn1n32008]

Each site with in the system will only be on a single band. VHF or UHF or 7/800MHz. I have yet to see, or hear of a multiband system that uses 900MHz

 

[kayn1n32008]

And how does the radio's input get affected by this?

I don't understand what you are asking.

 

[Pr999]

I don't understand what you are asking.

Well, you need to have the input frequency to access a repeater right? So when roaming, what happens with the input frequencies of the repeaters, how do they switch around? Or are they all the same between every repeater, coz you'd have to think that it would change per site right?

 

[dickie757]

And how does the radio's input get affected by this?

When a call is made on the active talkgroup, the subscriber allows the audio to go through.

The control channel tells the subscriber what frequency to transmit

 

[kayn1n32008]

Well, you need to have the input frequency to access a repeater right? So when roaming, what happens with the input frequencies of the repeaters, how do they switch around? Or are they all the same between every repeater, coz you'd have to think that it would change per site

each site will have assigned frequencies.

On 700MHz the inputs are fixed, 30MHz above the repeater output.

On 800MHz the inputs are fixed, 45MHz below the repeater output.

On UHF-low the inputs are 5MHz above the output.

On UHF T-band they are(I believe) 3MHz above the output.

On VHF-hi the input can be any split, depending on what is licensed for the site.

The input frequencies on a site don't change. With in the programming of the subscriber radio, there is a band plan that the radio uses to calculate the transmit and receive frequencies for each RF band rhat uses FDMA phase 1 trunking, and if capable, each band that uses TDMA trunking. On 700 and 800MHz these bands are fixed, on UHF and VHF these are custom set based on the frequencies assigned to the network operator. There can be multiple band plans for UHF and VHF trunking systems.

 

[Pr999]

When a call is made on the active talkgroup, the subscriber allows the audio to go through.

The control channel tells the subscriber what frequency to transmit

So the control channel controls also control the input frequencies as well? I only thought it controlled the output and middle.

Basically what your saying is, the system controls the radios?

 

[mmckenna]

Basically what your saying is, the system controls the radios?

Now you're getting it!

 

[Pr999]

Now you're getting it!

I just never knew it before since I still know little about trunking.

 

[kayn1n32008]

So the control channel controls also control the input frequencies as well? I only thought it controlled the output and middle.

Basically what your saying is, the system controls the radios?

On a P25 trunk system(and other control channel based trunking formats) when you key a subscriber radio, it transmits on the input frequency of the control channel repeater. In that transmission, it sends its RID, TG and requests a voice channel. It then un-keys, and if the RID is valid, and the TG is valid the controller will assign a voice channel and tell the subscriber to change frequencies to that assigned voice channel and transmit. The controller also tells all radios affiliated to that same TG, to go to the same voice channel and start passing receive audio from the transmitting subscriber. The subscriber will then change channels and begin to transmit on the assigned voice channel, and the transmitting subscriber(if its a Motorola radio) will emit the classic 'triple beep' talk permit tone.

 

[dickie757]

Here's where I get fuzzy.... Each site has, for example, 8 channels. Those are all repeater pairs? And the controller decides what call, on what TG, goes to which repeater? So that site has a total of 16 freqs, with one repeater acting as the control?

 

[kayn1n32008]

Here's where I get fuzzy.... Each site has, for example, 8 channels. Those are all repeater pairs? And the controller decides what call, on what TG, goes to which repeater? So that site has a total of 16 freqs, with one repeater acting as the control?

Correct. Each repeater has 2 frequencies. One is an input(receive) the other is an output(transmit) so a site with 8 repeaters will have 8 pairs of frequencies. A site with 20 channels, will have 20 pairs of frequencies.

Yes, the controller decides what channels get used, and does this by listening to the subscribers on the control channel input, and sends commands to control the subscribers on the control channel output. One repeater is used for the control channel.