Batboard

For decades police and fire agencies in the LA area have used activity beeps on the base frequency when mobiles are talking on the mobile frequency in order to let users know the channel is busy. The repeaters usually do not repeat the mobile traffic unless it is enabled by the console operator.

The question has arisen as to how and by what are the tones generated. Are they generated by the repeater itself when activity from the voter is detected or does it come from the console?

I seem to recall seeing this option in the Quantar RSS before I retired, while our agency didn't use it I have listened to LAFD, LACSO and CHP for years especially when Low Band was hopping.

Maybe you're thinking of 'channel marker?' I know an Orbacom TDM console I was dealing with once that the channel marker function got accidentally enabled on a channel, and it continued to put out a beep on the channel, and confusing every body until we could get out there, find it on the one console that had activated it and turn it off. It was a pretty new system, so dispatchers weren't familiar with all the ins & outs of the screen yet.

I'm pretty sure I've heard it on channels, UHF analog PD & I think 800 MHz trunked system here in Raleigh & Wake County.

No, the channel marker is a different animal altogether, intended for use when the channel is reserved for an incident and activated by the console operator manually. We too had that issue, someone activated it and didn't know it and couldn't figure out where it came from. The channel marker is typically a longer beep but spaced out further while the activity marker is shorter beeps closer together.

What they have in California is automatic, a low level beep from the repeater that, while similar to the channel marker, is active whenever the mobile channel is busy. The repeater is not active unless specifically enabled by the console operator so the beep reminds mobile units that the channel is busy. I *think* that it is activated by the voter being active but was wondering if the tone itself is generated by the console or repeater. Could it be generated by the voter?

Okay, it may be an SP or homebrew thing then (just guessing, like any good 2M repeater rat; talk at length about something I know little about).

BMT (before my time) - 30 plus years ago - a club repeater here would turn on a beep if AC maind dropped & it was running on battery. Homebrew controller plus not reliableble power.

Not sure what exactly you're mentioning - but I am used to hearing the "channel hold tone" when a console or emergency button is depressed and "locks" the trunked system to prioritize that emergency talkgroup. You'll hear a periodic beep until the emergency is cleared.

These are actually on conventional repeaters. Back in the Low Band days CHP on 42 MHz. and LASO on 39 MHz. used to use them all the time, currently LASO still uses this system on UHF T-Band conventional repeaters. I don't know if CHP still uses it or not on low band.

Interesting.I know the "channel hold open" can be on conventional as well, but you'd hear audio over it as well not just a dead channel.
I've heard beeps come from simulcast, tone remotes, voted receivers, etc... but never like I said on a dead channel.

This is a fun mystery.

OK, now I think I understand; you said it's on the base frequency (output) when the mobiles are transmitting (on the input). Linding blash of flight.

So it acts like a remote base, half-duplex (2 frequencies), but does not (just like you said, but I glossed over!!) repeat the mobile traffic unless enabled by the console.

Backing out. I'll be interested to learn how this is done. Enlighten us, oh wise ones.

Exactly! While they are repeaters, the mobile audio is not actually repeated during routine operations, just a low level beep to indicate the fact that a mobile is talking. Since the other mobiles are listening to the base channel they would not hear the other mobiles and this prevents them from talking over each other.

LASD does have an interesting system design.

19 conventional dispatch repeaters.
16 "L-TAC" (local tactical) repeaters.
4 "A-TAC" (area tactical) repeaters.
30 "S-TAC" (star tactical) channels (simplex and repeated.)

All channels are on the 470-490 T-Band range

Portables are a mix of GE MR-K, XTS3000 and XTS5000 using pre GE-Star or MDC1200. APX8000s are being handed out slowly.

Each area has its own analog sloppycast unsynced simulcast (hence no PL/DPL is used on the output) dispatch repeater with a second L-TAC repeater channel for coordination during incidents.

During normal operation, audio is NOT repeated by the system. Instead a "busy tone" is injected into the repeater. When a pursuit or some other emergency situation arises, the dispatcher will initiate "the patch" which then repeats mobile units.

With 19 dispatch areas to monitor, LASD didn't want to employ 19 dispatchers. The reason behind the busy tone is dispatchers are essentially trunked.

Using this example:

It's a slow Sunday night, 3 dispatchers are working.


Dispatcher "A" is working Ch 3 "East LA" with a light call load.

Dispatcher "B" is working Ch 12 "South LA" with a moderate call load.

Dispatcher "C" is working Ch 9 "Compton" with a heavy call load.

Ch 10 "Malibu" is having a slow night with no calls whatsoever. Because of that, the repeater is "unmanned" and no traffic is heard.

A deputy decides to make a traffic stop and keys up on Ch 10.

The computer finds the least busy dispatcher of the three available, and assigns Ch 10 to her console. Now Ch 3 and Ch 10 are linked together. Users on both channels hear the same dispatcher, but only hear beeps when a mobile unit is speaking. This allows one dispatcher to handle multiple channels with light call volumes simultaneously. In an effort not to confuse deputies from different areas, the busy tone is used.

During slow nights, it's not unusual to have 4 or more channels linked together.

Let's say the deputy gets into a pursuit on Ch 10. Dispatcher "A" will "turn on the patch" on Ch 10, which will offload Ch 3 to another dispatcher. Now Dispatcher "A" is handling Ch 10 exclusively, and all audio is repeated.

Here's an example of Ch 10 and Ch 3 being linked together, then separated when "the patch" is turned on. You'll notice when I hit nuisance delete (before the patch,) the beeps continue on the linked channel.

https://www.youtube.com/watch?v=8yWNarbVb4k

Channels time out after a predetermined amount of inactivity, and will be removed from an assigned dispatcher. Some deputies will kerchunk their radios occasionally to make sure they're working properly.

One of my favorite things about living in LA is most of our public safety is still analog UHF T-Band, so it's still wideband. Gonna miss the DigiTAC clicks and SpectraTAC chirps when they're gone. The county is slowly replacing them with SNV-12s.

mikegilbert wrote:Gonna miss the DigiTAC clicks and SpectraTAC chirps when they're gone. The county is slowly replacing them with SNV-12s.

SNV-12's still chirp if the dip switch to disable it hasn't been flipped.

I put in a lot of the infrastructure in some of the small cities in LA County.