CHP Golden Gate-SF Region

[gmclam]

CHP

why was I hearing base and mobiles corresponding solely on the 42.440 frequency since like forever,

The mobiles could have been talking car to car or you could be hearing the mobiles "repeated" through the dispatcher's console.

then in the last couple weeks, it's base on 42.440, and now weak mobiles responding on 42.760?

Which is quite normal. As mentioned, don't expect to pick up mobiles (even if you are 'behind' them) with your rubber stock antenna. At the very least you need an antenna outside of the vehicle, and ideally tuned for low band VHF.

 

[ridgescan]

ok gmclam-appreciate all the answers here BTW my observations of this issue were mainly on the home base scanner on the d130j. I run a Larsen Tribander in the truck but rarely listen to CHP on it. When I do, I run 42-43megs into search mode and I'll pick up reliable CHP base comms, but mobiles only if I'm very near them. In the truck, I won't be paying attention to what frequency I'm getting them on as I'm busy driving if I hear CHP mobile when on the road, it's safe to assume I had better be going the limit.

 

[scottyhetzel]

They have to repeat what they said to the other unit. I've heard it happen. They know the drill and it's no big deal. The dispatcher has no way to to know if anyone is talking car-to-car at the time.

The CHP mobile radio microphones actually have two transmit switch positions. One labelled "C-S" and the other "C-C."

C-S stands for "Car-to-Station", which means the mobile radio is listening on the Base frequency and transmitting on the Mobile frequency (which is what the dispatcher hears).

C-C stands for "Car-to-Car", which means the mobile radio is both listening and transmitting on the Base frequency.



There is simply no way this is true, because that's not how the CHP radio infrastructure works. If the dispatcher hears the unit, they must be transmitting on the mobile frequency because that's what is monitored by the dispatcher. If you didn't hear them on the mobile, perhaps you weren't behind the right unit, or the mobile frequency was programmed incorrectly? Antenna also plays a huge role when monitoring CHP. If you don't have a low-band external scanner antenna on your vehicle (like the mag-mounts sold at radioshack for example), it's very easy to miss traffic on the mobile frequency even when the unit is very nearby. Stock rubber duck antennas are terrible for monitoring CHP, and barely receive the base frequency in many areas.

I thought i was listening to The red being repeated in my area, but now i think of it it was mobile to mobile on the base freq.? I do have an 15x with an bad a$$ austin spectra roof mounted. It pullS in vhf low awesome. Thanks for the info. Very interesting.... I thought the C-C switch was for the VrS ...but i was wrong.

 

[inigo88]

I thought i was listening to The red being repeated in my area, but now i think of it it was mobile to mobile on the base freq.? I do have an 15x with an bad a$$ austin spectra roof mounted. It pullS in vhf low awesome. Thanks for the info. Very interesting.... I thought the C-C switch was for the VrS ...but i was wrong.

For the GE/Pyramid Extenders (now being phased out by the 700 MHz VRS system), there was a RPT button on the GE RANGR mobile radio so the officer could turn it on while exiting the vehicle while on portable. The VHF portable extenders had several channels, including one that controlled the vehicle's mobile radio in C-S mode, another that controlled it in C-C mode, and a third that was simply portable to portable. With only one extender frequency for most of the state (I think there was a second one in the NE corner of CA), these modes were controlled with different PL tones, and portable to portable was just CSQ. CLEMARS (now CALAW) was also programmed along with local agency channels for that area office.

One cool thing about the old extenders that I only recently learned, was that every time they were turned on they sounded a long beep tone. This tone told any other extender in range to switch off, and was important to prevent interference when multiple patrol vehicles were on scene at the same incident. Thus as each new patrol vehicle arrived on scene, their vehicle became the new extender... But this system wouldn't work if the officers forgot to turn their extenders OFF the last time.

I think gm already posted, but this website is excellent for CHP radio history:CALIFORNIA HIGHWAY PATROL MOBILE RADIO EQUIPMENT 2001

 

[ridgescan]

It sounds to me like what you were hearing originally was the mobile re-transmit on the base channel, and you were within range of the transmitter site. The second instance the mobile re-transmit has been turned off, and you are only hearing the mobiles on their mobile frequency, and since (as explained above) they are lower power, you are not hearing them as well (or at all).

See my next post for a more detailed explanation of how the mobile re-transmit system works.

A bit of explanation on how the mobile re-transmit works:

The mobile repeat function is not routed through every transmitter site in each area. The mobile repeat in each area is routed through only select mountaintop transmitters to avoid simulcast problems.

For example: Here in my area (I-80 corridor Roseville to Truckee), CHP Green has eight transmitters on the Green channel scattered through El Dorado, Placer, and Sierra counties. The mobile audio is routed out through only one of these towers, Banner Mountain in Nevada City. This site wase chosen to give the widest coverage for the area without causing feedback problems common with simulcasting audio without synchronizing the patterns (I know I am not using the correct terminology, but the theory is sound). It is possible there is one more re-transmit site down in El Dorado County, but I'm not certain of it.

For the Truckee channel (Gray), they use two mobile audio re-transmit sites: Howell Hill in Colfax for the Dutch Flat units west of Donner Summit, and another site (unk which) in the Truckee area for those units east of the summit. Due to terrain, synchronization is not an issue.

This information came from one of our state radio techs, who maintains both our system and the CHP system.

I'm sorry I missed your posts in here Duster-I do this too often for some reason (brain getting rusty)
Good info you put here

 

[inigo88]

inigo88-to add your theory to my OP, how about taking a crack at MY original question with your expertise:
why was I hearing base and mobiles corresponding solely on the 42.440 frequency since like forever, then in the last couple weeks, it's base on 42.440, and now weak mobiles responding on 42.760?

My best guess is this...

You've already seen duster and gmclam explain that the CHP system uses console repeat most of the time, which allows the dispatcher to route what the officers say on the mobile frequency back through the base frequency (as if it's a repeater). You no doubt understand repeater operation, by which a mobile transmission on the input frequency is boosted in power and repeated on the output frequency over a wide area.

Your scanner has a delay time built in. This delay exists so that if the scanner stops on an active frequency, it has time to hear a reply before it continues scanning. I would imagine that when your scanner would stop on the base frequency while the dispatcher was transmitting, that delay time would keep it on the base frequency long enough for you to hear the officer's reply repeated over the base frequency. It appears that they are both on the base frequency (and the officer is high power), but knowing what we know about the CHP radio system you are actually hearing the officer's reply on the mobile frequency being repeated over the base frequency at high power.

Fast forward to when they turned console repeat off. Now your scanner stops on the dispatcher, waits that pre-programmed delay time, then resumes scanning when it doesn't hear anything else on the base frequency. The next frequency it stops on is the mobile frequency, where you hear the officer replying. This gives the illusion that the officer moved from the base frequency to the mobile.

In actuality, the officer was always replying on the mobile frequency, but your scanner stayed on the base frequency due to its pre-programmed delay time. The only thing that changed was that the console repeat mode was turned off, causing the scanner to continue scanning and find the officer's low power transmission on the mobile frequency.

Does this make sense now?

 

[ridgescan]

makes sense but doesn't pertain in this instance.
Firstly, I hate delay so I leave it off. Secondly, it all started when, because I always got base/mobiles on 42.440, I was listening one day a couple weeks back and started noticing only one side (base) so I sat at the radio and started up 42.760 and sure enough, the mobiles were and have been since, only on 42.760 and seemingly on simplex. Thanks for responding here just something to have to adjust to. It's not drastic, just was wondering if anyone here was privvy to why the obvious change.
Thanks all-dead horse now.

 

[kma371]

Still doesn't seem like your understandng. The mobiles have, and will always be on 42.760. That is the input for the dispatch to hear them. UNLESS they are talking simplex to another unit, then they will be on 42.44. It has always been this way. There hasnt been a change to operations except the relay is off.

The reason you heard the mobiles so clearly on 42.44 before is the dispatch can repeat the mobiles onto the base freq. In the situation now it seems like that relay is OFF and you aren't hearing the mobiles as clear as you used to be.

makes sense but doesn't pertain in this instance.
Firstly, I hate delay so I leave it off. Secondly, it all started when, because I always got base/mobiles on 42.440, I was listening one day a couple weeks back and started noticing only one side (base) so I sat at the radio and started up 42.760 and sure enough, the mobiles were and have been since, only on 42.760 and seemingly on simplex. Thanks for responding here just something to have to adjust to. It's not drastic, just was wondering if anyone here was privvy to why the obvious change.
Thanks all-dead horse now.

 

[inigo88]

My head hurts. If you turn a repeater off what do you have? Dispatch talking on the repeater output frequency and mobiles talking on the repeater input frequency. That's what happened here, only CHP uses a more convoluted repeater process by relaying the mobile audio through their dispatch consoles.

They were always on 42.76!
You were hearing mobile repeat on 42.44, until it was turned off by the dispatcher.
Before you didn't need to listen to both. Now you do.

 

[ridgescan]

KMA371 you remember in post #7 your answer to me-I accepted that in post #8 as what's going on. Then others chimed in. Then I made the mistake of asking inigo88 for his thoughts. Now his head "hurts". Please. Wish I didn't ask.
In post #1 I say that I'm aware that 440 and 760 have always been base/mobile.
I understand perfectly what you stated in post #7 KMA and accept it as the answer. I am done with my thread as I wanted to be in post 27.
Inigo88-won't bother you in the future.

 

[inigo88]

Just a humorous comment, since we were obviously going around in circles beating the dead horse. No need to take offense. In #27, you disagreed with me, yet you accepted KMA's answer... yet he and I were both explaining the same thing. Surely you could see why this is frustrating. In any case, I'm glad we could help explain the system better.

 

[gmclam]

CHP

I thought i was listening to the RED being repeated in my area, but now i think of it it was mobile to mobile on the base freq.? I do have an 15x with an bad a$$ austin spectra roof mounted. It pullS in vhf low awesome. Thanks for the info. Very interesting.... I thought the C-C switch was for the VrS ...but i was wrong.

The first clue as to what you were hearing is to look at the CT value. IMHO a scanner with CT decoding is a requirement for CHP listening/scanning.

I listen heavily to CHP, whether base or mobile. I have the entire state programmed because VHF low band signals can travel quite the distance and I do pick up distant stuff. I also program the MOBILE frequency immediately following the BASE frequency for every pair. This way when the repeat function is turned off, I'll pick up the mobile on their native frequency if within range.

Another trick I'll do; when the repeat function is off, and there is an incident going on, I'll set the base channel to the priority channel and park the scanner on the mobile freq (or visa versa) with PRI on. It's like just scanning two freqs (but not as elegant) and let's me hear both sides on modern scanners. My PRO-77 handles this stuff automatically.