What does Dec/Hex mean?

[Jeremy1873]

The Wildland Fire Operations you show are a CONVENTIONAL system. In the conventional system, a separate frequency is dedicated for each group of users (channel).

Talk Groups are used in TRUNKED systems. In a TRUNKED system, a larger number of users/groups share a smaller number of frequencies. Each time a member of a talkgroup starts to transmit, a central computer assigns all members of that talkgroup to an available frequency. Unlike a conventional system, each frequency/channel is not dedicated to any particular group of users. Instead, a pool of frequencies is shared among a larger number of users. In a typical trunked system, frequencies may be shared among police and fire departments, utilities, buses, dog catchers, etc. It is very unlikely that all users in each agency will transmit at the same time, so the trunked system can get by with fewer frequencies than users. Users in a trunked radio system are organized into groups known as talk groups. A large agency like a police department may have numerous talk-groups organized similarly to the channels in a conventional system.

Above is derived from:

Radio Scanner Guide - Part 3A: Monitoring Trunked Systems - Police, Fire, Medical, & Business

A guide to selecting Radio Scanners; divides both new and used radio scanners into 6 categories, based on their specifications and features - e.g. analog trunking scanners, digital trunking scanners, etc; provides specifications on each model

radio-scanner-guide.com

Hello, I just want to start off and say this was very helpful. My question however is when you say "Unlike a conventional system, each frequency/channel is not dedicated to any particular group of users" you're trying to say for example PD assiagned channel 1 and that's it, while trunking PD can go from channel 1 2 3 right?

 

[Jeremy1873]

yea, could be 2 or more users, could be a paging only channel, could be a dispatcher talking a unit, really anyone who needs to talk. In the most simple way and I'm sure you already heard this in different ways. The deal is since trunking is a pool of frequencies which the computer system selects the next available free freq from the pool, there needs to be a way to distinguish the voices or else everytime someone presses the mic it would be like scanning all the frequencies hearing everything. So a talkgroups individual hexadecimal address becomes what was once individual frequencies and separate the voices on all the freqs so you only hear the voices you want to hear in your same group(talkgroup)

First off this was very helpful so thank you in advance, So in summary a conventional system it will broadcast to every frequency for example if E1 transmits on 782.213 people on the frequency 732.321 can hear them? While in a talkgroup for example 729 only people in that talk group can hear you.

Again I'm so confused on this pool/trunking part. So when you say "the computer system selects the next available free freq from the pool", here's where I get confused. Let's say Dec 727 is occupied by dispatcher 1 dispatching E1 to a medical aid, then Dispatcher 2 needs to dispatch E2 to a fire would that Dispatcher be moved? ( the computer system selects the next available free freq from the pool) If you understand where I'm confused. Or Engine 3 is transmitting on 723 to dispatch then E4 needs to transmit on 723 as well the zone channel would they get switched to "an available frequency from the pool". I hope you can see my confusion

 

[RMason]

Hello, I just want to start off and say this was very helpful. My question however is when you say "Unlike a conventional system, each frequency/channel is not dedicated to any particular group of users" you're trying to say for example PD assiagned channel 1 and that's it, while trunking PD can go from channel 1 2 3 right?

I think you are starting to get it.

In your Conventional example, 154.175Mhz is always assigned to County Wide Fire Command 1.

In the San Diego Trunked System, Northern Dispatch 1 (TG-208) can be assigned to any voice channel. For the San Diego Simulcast site, there each time a user of TG-208 keys up, there are 19 frequencies the call can be assigned to. (any frequency not used as the control frequency).

 

[Jeremy1873]

I think you are starting to get it.

In your Conventional example, 154.175Mhz is always assigned to County Wide Fire Command 1.

In the San Diego Trunked System, Northern Dispatch 1 (TG-208) can be assigned to any voice channel. For the San Diego Simulcast site, there each time a user of TG-208 keys up, there are 19 frequencies the call can be assigned to. (any frequency not used as the control frequency).

View attachment 109649

So is DEC 723 one channel or are there multiple frequencies within that one DEC channel 723?

 

[RMason]

First off this was very helpful so thank you in advance, So in summary a conventional system it will broadcast to every frequency for example if E1 transmits on 782.213 people on the frequency 732.321 can hear them? While in a talkgroup for example 729 only people in that talk group can hear you.

Again I'm so confused on this pool/trunking part. So when you say "the computer system selects the next available free freq from the pool", here's where I get confused. Let's say Dec 727 is occupied by dispatcher 1 dispatching E1 to a medical aid, then Dispatcher 2 needs to dispatch E2 to a fire would that Dispatcher be moved? ( the computer system selects the next available free freq from the pool) If you understand where I'm confused. Or Engine 3 is transmitting on 723 to dispatch then E4 needs to transmit on 723 as well the zone channel would they get switched to "an available frequency from the pool". I hope you can see my confusion

The system you are referring to here is San Diego-Imperial County RCS NextGen Trunking System, Various, California - Scanner Frequencies

TG-727 is Dispatch 1A ("Heartland"). If Dispatcher 1 is talking on TG-727, Dispatcher 2 will have to wait until Dispatcher 1 completes. On a trunked system only one user at a time can talk on a talkgroup. The system prevents all other transmissions on that talkgroup. If another user keys up they get a busy tone and their radio won't transmit and interfere with the transmission in progress.

Each time a user keys up, the controller will assign a frequency to the Talk Group.

An example:

Dispatcher 1 on TG-727 dispatches E1 to a medical aid; Call could be assigned to 851.0375 (available voice channel)
Dispatcher 2 on TG-727 dispatches E2 to a fire (waits until Dispatcher 1 completes); Call could be assigned to 841.4125 (any available voice channel)

E1 moves their traffic to TAC 1D (TG-27). Controller will assign new voice channel for each transmission.

E2 moves their traffic to TAC 1E (TG-53). Controller will assign new voice channel for each transmission.

The frequencies available on each site are shown in the System Frequencies portion of a Trunked System in the RR database.

 

[RMason]

So is DEC 723 one channel or are there multiple frequencies within that one DEC channel 723?

DEC 723 is a Talk Group. The controller will assign each transmission to an available voice channel (frequency).

 

[Jeremy1873]

TG-727 is Dispatch 1A ("Heartland"). If Dispatcher 1 is talking on TG-727, Dispatcher 2 will have to wait until Dispatcher 1 completes. On a trunked system only one user at a time can talk on a talkgroup. The system prevents all other transmissions on that talkgroup. If another user keys up they get a busy tone and their radio won't transmit and interfere with the transmission in progress.

So on a trunked system Dispatcher 2 can't interfere if TG727 is occupied while on a conventional Dispatcher 2 could interfere on that frequency.

Dispatcher 1 on TG-727 dispatches E1 to a medical aid; Call could be assigned to 851.0375 (available voice channel)
Dispatcher 2 on TG-727 dispatches E2 to a fire (waits until Dispatcher 1 completes); Call could be assigned to 841.4125 (any available voice channel)

So for this if Dispatcher 2 can't interfere with Dispatcher 1 and has to wait then why would Dispatcher 2 move to a new frequency "841.4125" if the frequency dispatcher 1 used "851.0375" would be free because they finished their transmission.

E1 moves their traffic to TAC 1D (TG-27). Controller will assign new voice channel for each transmission.

E2 moves their traffic to TAC 1E (TG-53). Controller will assign new voice channel for each transmission.

Then after the dispatch channel E1 would move to TAC 1D and that TG "TG-51" will still use that frequency pool in the picture, it's just that they're not on the TG 727 anymore they're on the TG-51 and any unit on TG-51 will be moved to that frequency if E1 transmits anything

 

[RMason]

So for this if Dispatcher 2 can't interfere with Dispatcher 1 and has to wait then why would Dispatcher 2 move to a new frequency "841.4125" if the frequency dispatcher 1 used "851.0375" would be free because they finished their transmission.

There are many Talk Groups on the system. Another user on another Talk Group may have keyed up before Dispatcher 2. The original frequency (851.0375) may not be free.

 

[Jeremy1873]

There are many Talk Groups on the system. Another user on another Talk Group may have keyed up before Dispatcher 2. The original frequency (851.0375) may not be free.

So trunk is sort of like one line at the bank that turns into 3 bankers while a conventional system is 3 lines 3 bankers. It's just which ever is available

 

[RMason]

Then after the dispatch channel E1 would move to TAC 1D and that TG "TG-51" will still use that frequency pool in the picture

The frequency pool shown in that picture is used for all Talk Groups that are affiliated with that site. A site can can support many more Talk Groups than the number of frequencies in the pool.

 

[Jeremy1873]

The frequency pool shown in that picture is used for all Talk Groups that are affiliated with that site. A site can can support many more Talk Groups than the number of frequencies in the pool.

So basically all those talkgroups are affilated within those frequencies and question, is a primary control channel and alt. control channel off limits?

 

[RMason]

So basically all those talkgroups are affilated within those frequencies and question, is a primary control channel and alt. control channel off limits?

Any frequency not being used as the control channel can be used as a voice channel (assigned to an active Talk Group). The control channel is off-limits. The primary control channel frequency is usually used as the control channel. The site may switch to an alternate control channel if the primary channel fails, if doing maintenance, etc.

 

[Jeremy1873]

Any frequency not being used as the control channel can be used as a voice channel (assigned to an active Talk Group). The control channel is off-limits. The primary control channel frequency is usually used as the control channel. The site may switch to an alternate control channel if the primary channel fails, if doing maintenance, etc.

So instead of 19 frequencies it’s really just 3 because of the control channels right?

And what’s a site?

 

[RMason]

So instead of 19 frequencies it’s really just 3 because of the control channels right?

And what’s a site?

In this example, the site has 19 frequencies. One frequency will be used as the control channel. 18 are available for voice channels.

A trunking system is typically composed of multiple sites to cover a large area. Think of a site as a tower that has its own set of trunked frequencies.

 

[Jeremy1873]

In this example, the site has 19 frequencies. One frequency will be used as the control channel. 18 are available for voice channels.

A trunking system is typically composed of multiple sites to cover a large area. Think of a site as a tower that has its own set of trunked frequencies.

Okay so the control channel is the one off limit but the alternate is available. Also does radio reference provide what department or TG uses which simulcast?

 

[RMason]

In general, RR does not provide what Talk Groups are affiliated with each site.

(Simulcast is a whole different topic.) Some sites are simulcast - multiple towers broadcasting the same traffic on the same frequencies

 

[Jeremy1873]

In general, RR does not provide what Talk Groups are affiliated with each site.

(Simulcast is a whole different topic.) Some sites are simulcast - multiple towers broadcasting the same traffic on the same frequencies

Thanks for the info. I’d just like to define everything I’ve learned and let me know if I need to correct or not

trunking: a system to not interrupt transmissions and assigns units to frequencies automatically

TG: a pool of frequencies

Simulcast: ?

Site: tower

Dec/hex: talkgroup?

 

[RMason]

Key Definitions

• Trunking: Trunking is a way to use a relatively small number of available radio frequencies in such a manner that allows a compartively larger number of distinct user groups to have their own "channels" of communication without assigning them to one exclusive specific radio frequency (that never changes, as in "conventional" radio systems). A trunked radio system allows conversations between many more groups of users (Talk Groups) than the number of frequencies.

• Talk Group: A 'talkgroup' is an assigned logical group of users on a trunked radio system.

• DEC/HEX: A numerical identifier for a Talk Group. (This can be represented in either Decimal or Hexadecimal format)

• Simulcast: Simulcast refers to the process of transmitting the same signal from different tower locations over the same frequency at the same time. A simulcast site is composed of multiple tower locations.

 

[Jeremy1873]

Key Definitions

• Trunking: Trunking is a way to use a relatively small number of available radio frequencies in such a manner that allows a compartively larger number of distinct user groups to have their own "channels" of communication without assigning them to one exclusive specific radio frequency (that never changes, as in "conventional" radio systems). A trunked radio system allows conversations between many more groups of users (Talk Groups) than the number of frequencies.

• Talk Group: A 'talkgroup' is an assigned logical group of users on a trunked radio system.

• DEC/HEX: A numerical identifier for a Talk Group. (This can be represented in either Decimal or Hexadecimal format)

• Simulcast: Simulcast refers to the process of transmitting the same signal from different tower locations over the same frequency at the same time. A simulcast site is composed of multiple tower locations.

Just want to thank you for all this information. I’ve been confused for days but the pictures you provided to give me that visual idea really helped so thank you for helping me on that. If I have any more questions I’ll make sure to reach out. Thank you

 

[Jeremy1873]

The system you are referring to here is San Diego-Imperial County RCS NextGen Trunking System, Various, California - Scanner Frequencies

TG-727 is Dispatch 1A ("Heartland"). If Dispatcher 1 is talking on TG-727, Dispatcher 2 will have to wait until Dispatcher 1 completes. On a trunked system only one user at a time can talk on a talkgroup. The system prevents all other transmissions on that talkgroup. If another user keys up they get a busy tone and their radio won't transmit and interfere with the transmission in progress.

Hey I had a question about the interference part. So lets say someone is talking on TG-727 then a unit on TG-729 needs to transmit will they still not be able to transmit or will they just get assigned an available frequency? Or would the unit on TG 729 have to wait until the unit on TG 727 is done