CHP Base Channel vs Mobile Channel (and Mobile Extenders)

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CopperWhopper67

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What is the functional difference between the base channel of a certain color and the mobile channel of that certain color?

Also, what's the difference between the 700 MHz extender listed with each color channel, and the universal VHF mobile extender listed after the Division listings?

Thanks!

P.S. Can someone also describe the usage of the Remote Links?
 
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kma371

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The base/mobile is exactly that. The base talks on the base and the mobile talks on the mobile. Some divisions have gone to repeaters and the base is now the outout and the mobile is the input.

700 extenders replaced the vhf extenders for much of the state. Each office uses a specific 700 extender.
 

CopperWhopper67

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The base/mobile is exactly that. The base talks on the base and the mobile talks on the mobile. Some divisions have gone to repeaters and the base is now the outout and the mobile is the input.
So, if I'm understanding correctly then an officer would use the Base to talk to Control, and the Mobile to talk to another car?
 

scottyhetzel

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So, if I'm understanding correctly then an officer would use the Base to talk to Control, and the Mobile to talk to another car?
No mobile is the tx from car to station... dispatch uses base to tx to the units. Cruisers listen on base...transmit on mobile...

Remote links are repeater to repeater.. not used by units...just for dispatch to cover larger areas...
 

Station51

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CHP

The "BASE" is in effect the DISPATCH channel and the "MOBILE" is the frequency that the vehicle transmits on or answers dispatch.
If you were close to a mobile unit and listening only to the mobile frequency you would hear only the unit.

As pointed out some areas now use repeaters enabling listeners to hear both sides of the conversation.

In previous years a scanner listener would only hear the BASE or dispatch channel and would have to scan the MOBILE freq and hope that the unit was nearby in order to hear that side of the conversation.

The extender basically is a handheld radio that transmits to the vehicle and is relayed thru the low band vehicle radio.( An extension of the mobile radio) They are actually called "mobile extenders" This was set up because low band handheld radios are cumbersome and require a long antenna and even then aren't too efficient.

The old extender freq of 154.905 could be monitored while driving and if you heard a strong signal you could be sure a unit was close by.

They (Uniden) came out with a "bear tracker" that monitored that freq so that drivers could take advantage of the signal, somewhat like a radar detector.

In response the CHP modified the extenders to emit a loud beep once the vehicle was rolling so that the officer would turn off the extender thereby removing the possibility to know that they were close by.
 

zz0468

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To put it another way, the base stations transmit and receive on different frequencies. A "channel" (copper, for example) will have two frequencies associated with it, not just one. The base station transmits on one frequency, which the mobile listens to. The mobile transmits on the other frequency, which the base listens to.

The base may or may not be a repeater. The hardware is essentially the same, but as a repeater, the base station transmits what it hears on it's receiver at the same time. Then, mobiles would hear other mobiles as well as the dispatcher does.
 

allend

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So this is how the CHP Cruisers work. They use the mobile input frequency to hit The CHP voter repeaters which are radio over IP back to dispatch consoles or Microwave linked. Most chp base frequencies are repeated in the metro areas. In the desert stretches or communities the CHP base frequencies are not repeated. You will have to program in the mobile input frequencies to hear them if they are close. The HT APX portable radios that they carry on their waist are 700 mhz radios. They transmit on 700 mhz back to their vehicles in simplex direct mode into a 700 mhz radio in their cruisers. Then the 700 mhz transmissions get converted and transmitted out of their cruiser on VHF low band back to dispatch.

Now the car to car function is either transmitted on Channel 1 which is their main dispatch channel which is either repeated in metro areas. But most of the time the car to car is transmitted on Channel 2 and the channel 2 frequency is programmed this way. Usually units lets say are transmitted on lets say RED Indio system. The base frequency is 42.44 and the mobile transmit input frequency is 42.28. They transmit on 42.28 which is input and received and dispatch transmits back on 42.44.

Car to car works this way. Most of the time you can't hear car to car most of the time unless you are close within a few miles. They would not transmit on the input frequency. They will use simplex which is setup on Channel 2 and they transmit car to car on 42.28. So transmit and receive is all done on 42.28. And also, I am not sure if dispatch can even hear them on Channel 2 unless they have a way to listen since I am not sure how their dispatch consoles are setup.
 

ME801

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The VHF extender frequency of 154.905 is no longer in use, they migrated to the 700 MHZ band for the extenders when CHP got the APX's.
 

kma371

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The VHF extender frequency of 154.905 is no longer in use, they migrated to the 700 MHZ band for the extenders when CHP got the APX's.
I don't know if that's entirely true. I believe some northern rural officers still use 154.905.
 

norcalscan

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Car to car works this way. Most of the time you can't hear car to car most of the time unless you are close within a few miles. They would not transmit on the input frequency. They will use simplex which is setup on Channel 2 and they transmit car to car on 42.28. So transmit and receive is all done on 42.28. And also, I am not sure if dispatch can even hear them on Channel 2 unless they have a way to listen since I am not sure how their dispatch consoles are setup.
Correct me if I'm wrong, their "Channel 2" would actually be their base channel setup in simplex mode, so they actually transmit on the "base" channel 42.440 so other units who are normally listening on base would hear them. There is no "car-to-car" ever done on the "mobile" 42.280 side of their radio system. This is why dispatch doesn't hear them, they aren't listening on Base. I've heard officers mocking their dispatcher or other snide remarks on car-to-car that the dispatcher would have personally hunted them down had they heard it. :roll:

One nice benefit to how their radios are setup is at any given moment, dispatch can talk and have precedence on everyone's radio. A mobile transmitting will never 'tie up" a repeater like a mobile on a normal repeater would. If a mobile is talking, dispatch can still hear the mobile WHILE transmitting on base, and in car-to-car mode, dispatch would typically override the mobile by sheer power.

On areas where the mobile is "repeated" on base, it is simply an audio patch at the dispatch console, not an actual "repeater" as you and I typically understand them.
 

techman210

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This is why dispatch doesn't hear them, they aren't listening on Base.
This is not entirely true everywhere in the state. I have heard the dispatchers respond to units that are on "Channel 2" or mention "Unit xx-xxx, You are on Channel two". This is likely done by a local antenna and radio at the dispatch center.

BTW, A lot of the analog 72 MHz links have gone away, and moving to traditional microwave or the 900 MHz MAS spectrum - both digital.
 

techman210

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72MHz links alive and well in northern and central California.
That's good to know. A lot of the Calif State infrastructure is amazingly old and getting harder to support. It seems the path to upgrade is to "wait for it to fail and then replace it", rather than having systematic, planned upgrades. The only downside of the midband VHF stuff is single-channel audio transport for a pretty sizable antenna on the tower when low-density mux radios are available that carry 12x or more of the traffic.
 

scannerboy02

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I am trying to program a Unication G5 with the 16 VRS frequencies and the Unication PPS is requiring me to input a TGID for the channels.

For now I have used TG 'FFFF' but I'm not sure if that will actually work. Does anyone happen to know the TGID(s) used by the VRS system?
 

kma371

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I am trying to program a Unication G5 with the 16 VRS frequencies and the Unication PPS is requiring me to input a TGID for the channels.

For now I have used TG 'FFFF' but I'm not sure if that will actually work. Does anyone happen to know the TGID(s) used by the VRS system?
There isn't a specific talkgroup. Just use the default and it will open the squelch. That's what I do. I use 65535 DEC
 

scannerboy02

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That's what I will do for now.

I guess I will make finding the TGID(s) part of my vacation fun next month.

My guess is they are using TGID to steer the VRS to the appropriate mobile radio and channel, depending on what "channel" the portable is tuned to. It is my understanding that they use the same frequency and NAC for all "channels" in the portable so something is making the audio go to the correct radio/channel in the car.
 

drsl2000

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Correct me if I'm wrong, their "Channel 2" would actually be their base channel setup in simplex mode, so they actually transmit on the "base" channel 42.440 so other units who are normally listening on base would hear them. There is no "car-to-car" ever done on the "mobile" 42.280 side of their radio system. This is why dispatch doesn't hear them, they aren't listening on Base. I've heard officers mocking their dispatcher or other snide remarks on car-to-car that the dispatcher would have personally hunted them down had they heard it. :roll:
.
This is not entirely correct, Channel 2 is the BASE frequency. Car to car simplex is done via channel 2 (the base frequency).

Also, the dispatch monitors Channel 2, because:
1) They want to avoid stepping on mobile communication (if possible) ,
and
2) They listen to monitor for tactical information, and many times will comment " Copy traffic on Channel 2" . I've heard this when the mobiles communicate on their location and offer to take each others calls based respective locations...
 

kma371

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That's what I will do for now.

I guess I will make finding the TGID(s) part of my vacation fun next month.

My guess is they are using TGID to steer the VRS to the appropriate mobile radio and channel, depending on what "channel" the portable is tuned to. It is my understanding that they use the same frequency and NAC for all "channels" in the portable so something is making the audio go to the correct radio/channel in the car.
That's not how it works. VRS is driven by input NACs, not talkgroups of any kind.
 
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