Need help (please!) with CHP

[LIScanner101]

I need a little help understanding how the CHP system works…

I looked at the database on this site and noticed a large number of low band frequencies, but ALSO a number of 700MHz band frequencies listed as “extenders”.

My questions are:

1. In order to follow a CHP conversation properly on the low band, do I need to program-in both the base AND mobile frequencies?
2. Related to #1, are the 700MHz frequencies listed as “extenders” really just “repeaters” that “repeat” what the low band Rx/Tx is? If that is the case, would I have to even bother listening to CHP on low band?

Thanks for any help!!

-John

 

[CHPMustang]

The "Extenders" are merely just Portable to Mobile when the officer is out of his/her patrol car. You can receive the VHF extender transmissions if you're within a mile of them as they are low powered less than a watt off the portable, but I would just scan the standard low band frequencies as their coverage is much more receivable.

There are many areas in California that CHP has their frequencies on repeaters thus you'd only need to monitor the base frequency but I would program both base and mobile in.

 

[mkewman]

Also try scanning the 72 mhz links listed. They are extremely powerful and in many areas, I receive them better than the 42 mhz repeaters.

 

[LIScanner101]

Also try scanning the 72 mhz links listed. They are extremely powerful and in many areas, I receive them better than the 42 mhz repeaters.

Sounds good. Can it be an "either/or" situation? In other words, is there stuff I'll here on the 30is/40is range that I won't hear on the 72 mhz links (or vise versa), or would I be missing stuff if I DON'T use the 72 mhx links? I just figured it would be best not to have too many duplicate sources of data.

 

[mkewman]

it's not an either/or situation, it's basically a link from the receive sites and repeaters to the comm center. It's the same stuff you should hear on 42mhz (in theory) it's just that you don't have a hilltop reception site with extremely expensive (military spec) equipment that picks up those units deep in the canyons and urban jungles. They've got the prime real estate and equipment, but at least they re-transmit it at 72mhz at high enough power for us to pick it up! hope that helps

 

[russianspd]

From my listening to my local CHP I have been able to listen to 90% just using the base frequencies. I can pick up mobile if the unit is really close to me, somewhere between 2-3 miles. Using just the base channel I can pick up both sides of the conversation between the two closest offices in my district. I can listen to one side usually whether it be the unit or dispatch of the two other offices that are out and east from my location. Also depends on if the dispatcher has their repeater turned on at their console from what I have read. (it re transmits the units transmissions)

I'd say for 90% converage having just the base and mobile channels will do fine. To get 100% plug in everything you can for your area and the rest is up to your location and the units and how the units and dispatchers have their systems configured at that given time.

 

[ScannerDude244]

where are you located at?

 

[gmclam]

CHP

I need a little help understanding how the CHP system works…

It really depends on WHERE you want to monitor, and how much of the traffic you want to hear. It is getting easier than it used to be to monitor both sides of each conversation, but not guaranteed by any means.

I see that you are in NY, so I wonder if you're trying to understand this from a technical point of view, or if you're planning a trip to California and don't want to miss anything. If you don't want to miss anything, it takes a LOT of effort. Heck, dispatchers and officers miss traffic from each other due to the vastness of this state and the fact no technology is 100%.

As I casual listener, just program in the BASE low band VHF frequencies and you're good. If you've got a proper antenna (which you really need anyway) and want a better chance of hearing mobiles, program in the MOBILE frequencies too. If you yourself are mobile AND have a digital scanner, then why not add in the 700 MHz Extender frequencies. That way you'll pick stuff up more clearly that you are close to.

There is a page in the Wiki that describes how the CHP system works. Each channel (pair) typically has multiple receive sites (on mountain tops) and a "voter system" to elect who is receiving the best signal. That signal is typically routed to the dispatcher who then typically replys on the same repeater, but can override it. That's the simple version. :lol:

 

[LIScanner101]

Hi gmclam,

Thanks for the great post. I do live in NY, but as I mentioned earlier I travel on business to CA a couple tines a month and have a lot of down-time while there. I plan on putting "an" antenna on a window sill of the hotel window and connecting it to my scanner via a run of coax. Hertzian gave me some great antenna tips, but I'm stuck on the actual understanding of what I really need to listen to.

I will focus on plugging in all the low-band base frequencies for now, since I came up with about 80 that should be plenty to listen to.

 

[LIScanner101]

where are you located at?

I'm going to be listening almost exclusively in San Francisco or San Jose. Once in a while I'll be in Los Angelos.

 

[oracavon]

All the channels in Los Angeles and Orange County have repeaters on the base frequency, so those are all you will need in Southern California. You should also include Southern Blue 3 for LA (45.42). LA uses it for sigalerts and pursuits that cross office boundaries.

 

[gmclam]

CHP

Get yourself a good VHF LOW band antenna. I just use MAG mounts and they are great. It really is the key.

The good news is that the Bay Area and Los Angeles are both in repeat mode most of the time and that will enable you to hear both sides of the conversation on the BASE frequency alone. Now if you're just "in the city" I don't expect problems. But if you should get in a hilly area or fringe part of the coverage, that's when having the mobile or extender frequencies programmed help.

 

[SCPD]

If you travel in areas away from the urban areas you won't hear the mobile traffic carried through on the base frequency. This is done because the units are more widespread and in topography where hearing the repeated base station is not possible for the majority of units. California is more than the megalopolis of southern California, the Bay Area and Sacramento. It is more than Disneyland and freeways. California has the tallest, oldest and largest trees in the world. It has the lowest point in the nation and the highest point in the lower 48 and incredible diversity in landscapes. I

I hope you have the time on one of your trips to see more of the state. When you do program the base and mobile frequencies!

 

[slo_z28]

The 700mhz is the repeater channel. The repeater repeats all traffic that the low band transmits, and can be tuned on manually or automatically turns on when any door is opened (and is very frequently never turned back off). This is of course only on the new "CPVE" crown vics (of which there are very few). Some of the old GE radio head cars had their extenders changed to meet with the new narrow banding requirements, and some (including my fleet) didn't.

Im just a mechanic , not a radio tech, but I did stay at a holiday in express a few weeks ago.

So, I am assuming somewhere on this site I can find out why new Bearcat 996XT scanners wont clone?

 

[LIScanner101]

If you travel in areas away from the urban areas you won't hear the mobile traffic carried through on the base frequency. This is done because the units are more widespread and in topography where hearing the repeated base station is not possible for the majority of units. California is more than the megalopolis of southern California, the Bay Area and Sacramento. It is more than Disneyland and freeways. California has the tallest, oldest and largest trees in the world. It has the lowest point in the nation and the highest point in the lower 48 and incredible diversity in landscapes. I

I hope you have the time on one of your trips to see more of the state. When you do program the base and mobile frequencies!

Thanks! Unfortunately when I do travel to CA it's all business and even with the downtime I can't wander too far, most likely it's just catching up on some office work in the hotel room (hmmm, doesn't sound like downtime to me LOL!)...

 

[gmclam]

Extender vs Repeater

The 700mhz is the repeater channel.

We call it an "Extender channel" which has a different definition than a repeater. Certainly it repeats what the officer's radio is selected to, but only for a short distance so as to extend his ability to use his/her radio when away from the vehicle.

A repeater typically has a high antenna (mountain top, tower, etc) which creates broad coverage of an area for a signal for which would otherwise not have the same coverage area (such as from a vehicle).

 

[commstar]

The extender is the CHP replacement to the 15' mic cord, radio traffic over PA, and microphone clips on pushbars.

Where lowband portable radios require rubber duck antennas the length of Florida (or worse yet metal antennas) and were not reliable.

So, CHP elected to go to a low-power crossband vehicle based repeater system deemed an 'extender'.

Extenders were utilized by many agencies on often on lowband and generally in rugged terrain or covering long distances where mobiles functioned far better than portables.

When lowband systems were common, so where extenders.

Extenders 'extended' the communication capability of CHP Officers beyond the length of the radio microphone cord of their mobile radio.

Mic cords were often so long that one could take the mic out to the pushbars and use the hood as a de-facto desk and leave the radio audio on PA repeat.

Often, patrol cars had microphone clips on the pushbars in part to keep the then metal bodied microphones abit cooler and to avoid open mics.

Certainly not a better time, but definitely a different time in LE communications.

Extenders have certainly saved many lives in public safety.

Mike
.

 

[SCPD]

While we are getting technical as to what an extender is and that it is not a repeater, lets remember that the CHP does not use repeaters at all. The CHP uses remote bases linked by microwave in most cases and 72 MHz links in some locations. The mobile frequency audio is patched over to the base frequency of a remote base. This is done at the option of the radio operator by using a feature that consoles have. The operator has the option of dropping the patch or patching the mobile audio through another remote base.

I was in a restaurant in the far north portion of Mono County one day and a CHP officer was sitting a couple of tables away. His extender (on 154.905) was fairly quiet. As happens so often the officer was called to a traffic collision before finishing his meal. He responded to the dispatcher in Bishop without taking the handheld off his belt.

After he left the people sitting between me and the officer remarked that the officer was able to talk to Bishop without even having to take the radio off his belt. They wondered why their CBs could not do that. I offered to explain the process and they were interested. I told them how the extender reached the car, which in turn was received by the nearest remote base. Then I explained how a 72 MHz link took the signal to the nearest microwave site and that three additional hops were required to get the signal to the dispatcher's console. I told that their CB would not even be able to make it to the nearest remote base in most conditions.

I then showed him my ham "extender," that connects the handheld to my mobile, which then worked a repeater linked to two others, allowing me to speak with my nephew on the west shore of Lake Tahoe and then demonstrated it. He was pretty impressed. I remember my first tunable scanner in 1968 and how I had no idea how VHF radio worked. The people who don't have much knowledge of radio, just like I was many years ago, don't understand why public safety agencies, like the CHP, need the budgets they do. I didn't even want to try to explain how a simulcast trunked system worked!

 

[scottyhetzel]

While we are getting technical as to what an extender is and that it is not a repeater, lets remember that the CHP does not use repeaters at all. The CHP uses remote bases linked by microwave in most cases and 72 MHz links in some locations. The mobile frequency audio is patched over to the base frequency of a remote base. This is done at the option of the radio operator by using a feature that consoles have. The operator has the option of dropping the patch or patching the mobile audio through another remote base.

I was in a restaurant in the far north portion of Mono County one day and a CHP officer was sitting a couple of tables away. His extender (on 154.905) was fairly quiet. As happens so often the officer was called to a traffic collision before finishing his meal. He responded to the dispatcher in Bishop without taking the handheld off his belt.

After he left the people sitting between me and the officer remarked that the officer was able to talk to Bishop without even having to take the radio off his belt. They wondered why their CBs could not do that. I offered to explain the process and they were interested. I told them how the extender reached the car, which in turn was received by the nearest remote base. Then I explained how a 72 MHz link took the signal to the nearest microwave site and that three additional hops were required to get the signal to the dispatcher's console. I told that their CB would not even be able to make it to the nearest remote base in most conditions.

I then showed him my ham "extender," that connects the handheld to my mobile, which then worked a repeater linked to two others, allowing me to speak with my nephew on the west shore of Lake Tahoe and then demonstrated it. He was pretty impressed. I remember my first tunable scanner in 1968 and how I had no idea how VHF radio worked. The people who don't have much knowledge of radio, just like I was many years ago, don't understand why public safety agencies, like the CHP, need the budgets they do. I didn't even want to try to explain how a simulcast trunked system worked!

Curious...why microwave a link via towers when you can use a T-1 ( hi-speed circuit) circuit from one tower to another. Which generally is less maintance and will stay in tact in a earthquake. Hence how parabolic dishes need great alignment to work. I understand some tower don't have dial tone... So in that case microwave will have to take priority. This is basically how most cellular towers work.. Most towers have only a T-1 circuit. Not sure if I'm hi jacking this post are not.

 

[mkewman]

Simply put, T-1 is much more expensive to install, operate and maintain. Also, as you said, the best hilltop sites, don't always have telco services.

Since there are CTA offices everywhere, and they all have tower climbers (they don't have to sub-contract out) all it takes after an earthquake is a quick phone call and someone's on their way to fix it.

Even though this is California, it's in better hands too. If they had T1, they'd have to call the phone company, who is too busy installing consumer level services to fix an "ancient" T1 line right away. I'm being slightly over the top here, but my point is, AT&T would take longer to fix a T1 line, than a trained State worker would take to climb a tower and move an antenna 3 degrees.

The other part of it is that T1 is not exactly Disaster proof. The CHP would be relying 100% on an infrastructure that isn't theirs. If that infrastructure were to go down, (as it has, as recently as a year or so ago in Nevada County... a telco line was snapped and half the county had no dialtone, internet, or t1 for more than a day) they'd be at the mercy of a publicly traded company, whose first priority is $$$ and not connectivity (they operate under the idea "eh, let's wait until 9am when the tech goes on duty, we don't wanna pay any overtime if we don't have to.")

Whereas with plain ole RF, it's fixed faster, and cheaper.

That's just my take. I could be wrong.