Monitoring CHP

[Sac916]

I've been a scanner enthusiast for a couple decades now, but I think it's about time a get educated.

I don't listen to CHP very much, mostly due to the excessive amounts of uninteresting chatter. The other reason is the inability to hear mobile transmissions. I have found it nearly impossible to hear a CHP patrol unit's transmission unless they are nearby. With various scanners and antennas, catching a patrol units transmission is not an easy task.

Now please educate me.

Why? Why is it so difficult to monitor CHP mobile units?

It boggles my mind that a CHP unit can transmit and hit a tower that is farther away than I am, yet I can't hear the CHP unit at all.

Excluding the mobile repeater, how do YOU monitor CHP?
What antennas do you use?
Metal whip? Rubber whip? A spider web of copper wire?
Do I need a discone antenna on top of a two story house?
100ft radio tower with an antenna that reaches the moon?

Educate me.

-Ant-

 

[bhesson]

I believe your best bet is to have an antenna that is matched for 42 mghz. short of that nothing beats altitude. but I do not think you will be able to compete with the altitude of the base units antennas. My mobile antenna is the same one the chp units actually use on their cars. I can't remenber the name of it but I bought it from Mudd Shack in La Mesa ca. Even with that antenna I still have to be reletively close to hear the mobile units. I guess it all comes down to PFM (Pure F***ing Magic)

 

[HBdigital1]

For some reason, the OC CHP offices have a repeater function on dispatch frequencies, where you can hear each unit's reply; why this isn't so in other surrounding counties, I don't know. It is interesting and fun though, with CHP's low band frequencies, to think how far the signal travels. Back in my days in Galveston, TX, attending school there, I was able to "snag" some CHP traffic via skip waves, and sure made me homesick, hearing of the "405" or "10" freeway, while spending time in "Longhorn" land. And all this low band skip was obtained thru my radio's telescoping antennae!!!!

 

[Spec]

Having lived in Northern California for a number of years I always found CHP system to be a fairly well thought out system. Now before some starts with not so....I'm speaking of before the last 20 yrs. Set up as a semi-duplex system it allowed for units to not interfere with base units on the same "channel" set up. It also allowed for much long range in and around hills etc. Mountain top recieve / transmit sites became more and more as time progressed. All in all it was and still is a pretty good system. Living on the east coast I compare the California coverage to NY to Ga. Each car / unit can go anywhere in California for the most part and talk with another unit. Try that on the east coast. lol OES also had a unique system. Lo band to the mountain and Hi band to the unit. I've always favored the lo band stuff. While 800 is good for urban areas it rots in the hills. I could go on and on, but your chances of snagging signal here on the east coast only makes my heart flutter when radios were radios. lol

Spec

 

[Kirk]

I'm lucky, I live in an area where CHP mobiles are patched into the base frequencies.

It's not a repeater system. A repeater would mean the signal goes up to the mountain on one frequency, goes through a set of duplexers, and comes out the same machine on a different frequency. CHP does things differently, in that the patching is done at the console, and the signal is sent out on only some of the mountaintops. It's low tech, but it works.

The other neat thing about CHP radios is that the microphones have a dual PTT (push to talk), where pushing one button results in contacting dispatch, and the other is car to car mode.

The best way to monitor them in an area where they don't patch the audio to the station freq is to have a good low band antenna as high as you can get it. They run quite a bit of power on those GE Rangr radios, but they switched to shorter loaded antennas (I thought the fender mount whips worked better), and can be hard to copy.

If they're real close you can listen on the mobile extender frequency (154.905 in most areas), but that's not very reliable.

 

[n4voxgill]

If you hook your scanner up to an frequency specific antenna that is on atower that is 300 to 400 tall, and fed with hardline that costs a couple of several per foot, then you could pick the cars up more often. This is why the base stations can hear the cars.

Of course with a scanner you might also be overloaded with garbage and not hear much after all.

 

[ray smith]

I use a Larson 6 meter ant in the car for CHP and works real well (works well for civ air too). The house I use a Discone up about 20 feet.

 

[DPD1]

Do I need a discone antenna on top of a two story house?
100ft radio tower with an antenna that reaches the moon?

As you go lower in the bands, having the proper antenna for that band becomes much more important. Unlike when you are dealing with normal UHF/VHF... You can say, have an antenna for VHF, and it will still pick up UHF stuff pretty well. But that doesn't happen when you start to go down into the single and double digit freqs. Having a vertical tuned for 42 MHz is the way to go, and wide band stuff like a discone isn't going to do very well. If you're just using a handheld antenna, then you will barely get anything. The base stations they use are probably running some pretty heavy power. You have me curious what they use now... I might drive by and see.

Dave
-DPD Productions - Custom Scanner, MURS, & Ham Antennas-
http://eje.railfan.net/dpdp/

 

[Mick]

It is a great thing for officers to not have to switch channels by having a rocker switch button on the microphone, push down to talk to dispatch, push up to talk car to car. With this there's no chance of forgetting to go back to the primary channel after being on a car to car channel.

I'm lucky, I live in an area where CHP mobiles are patched into the base frequencies.
The other neat thing about CHP radios is that the microphones have a dual PTT (push to talk), where pushing one button results in contacting dispatch, and the other is car to car mode.

 

[Kirk]

It is a great thing for officers to not have to switch channels by having a rocker switch button on the microphone, push down to talk to dispatch, push up to talk car to car. With this there's no chance of forgetting to go back to the primary channel after being on a car to car channel

Yeah, as far as I know, they're the only agency with such a setup. It's pretty neat. I think I have one of the old dual-ptt Micor mics in my garage somewhere.

 

[mkewman]

Try getting an antenna tuned spacifically to the CHP's frequencies... also, the higher up you are the better, chp's radiation angle is over your head not out to the sides, so the higher the better in most cases.

also, depending on your terrain, it may be impossible to recieve mobile transmissions.

some people find that a cheap rs discone outside, about 10 to 25 feet of the ground works good, but it's definitly something you must experiment with.

while it's a little longwinded, mike derryberry on the SCANnorCAL listserv summed it up best back in march (yeah i had to dig, but i found it):

Listening to CHP is probably one of the hardest agencies to listen to in
California. With their low band non-repeated system you need to be
within 10-15 miles to hear the cars talking to dispatch or car to car.
If you are mobile with a handheld you just about have to be on top of
them. I use a low band whip on my Bronco cut for 42mhz and can normally
hear the cars up to about 10 miles away.

For home listening I am using a modified 6m ham antenna on a 30 foot
tower on my roof and I live in the highest part of town. With this set
up I can normally hear the cars up to 20-25 miles away. Hear in
Bakersfield they have a 900 link from 1 of the mountain tops to the
local office that I am able to listen to almost all of the car traffic
on. Most of what I can't hear on the 900 link I can hear on low band.

I have spent hundreds of dollars over the years trying different
antennas and different types of coax cable trying to find what works
best. My home set up allows me to hear most all of Bakersfield cars on
the Brown, all of the Turquoise for I-5, Fresno on the Pink, San Luis on
the White, LA on the Tan, LA Altadena on the Brown (thankfully different
PL from Bakersfield), Bishop dispatch on the Gold for Mojave Desert,
occasionally Barstow on the White and normally Inland dispatch on the
Copper-1. Not too bad for being in the far south end of the valley.

Just try some experimenting, and don't get discouraged. CHP is very hard
to listen to. Depending on where you live, there are some areas of the
state where you may never hear a car unless they are in your area.

Hope this helps ... sorry if I was a little long winded ....

Mike

--

miked911@pacbell.net
Mike Derryberry

Dispatcher II
Kern County Sheriff's Department
Bakersfield, CA

so to conclude. there are three key things,

experimentation, height, and having an antenna tuned to the 42 mhz.

 

[1979lee]

great info, i live in bakersfeild, and i can't get the Copper-1 channel.

 

[Tweekerbob]

You can try building a coaxial dipole cut for 42 MHz. There are several great examples of these antennas floating around on the web. This is also the antenna that CHP uses at their offices and probably their towers as well.

You will not get great results with a discone, and for that matter, a ground plane 1/4 wave vertical tuned to 42 MHz will not yield as good of results as a coaxial dipole. This is due to the lower radiation angle exhibited by the coaxial dipole.

For your vehicle, the best suggestion would be the fender mounted true 1/4 whip, but these are pretty long and may be hard to find. I would then go with a loaded 1/4 whip, cut to 42 MHz. If you want to get down right quick and dirty the next best alternative would be this antenna http://www.antennawarehouse.com/Scanner/wep300.htm It's not pretty, but it is an excellent low band antenna. With this antenna stuck to the trunk of my car, parked in my driveway in El Dorado County, I am able to receive every CHP frequency from Eureka down to Monterey. About 13 CHP dispatch frequencies in all. Needless to say, it does a pretty good job with the mobiles, on average about 10-15 miles, although terrain can be a big factor up here in the hills.

Another alternative to hearing the mobile sides of transmissions is to use the 72-75 MHz links. Not all areas use these frequencies for their links, more and more are going to microwave, but there are still some areas that use them. These links will be able to hear 90+% of all of the mobile traffic.

Ryan

 

[sacscan]

I live in an apartment so I've been using the Radio Shack mag-mount antenna with the two center loads. I set it in the middle of the metal ducting that comes off the top of the heater/air conditioner. It seems to be a pretty good ground plane as I hear quite a few mobiles.

 

[qc]

Im using a Channel Master 5094A Base Antenna mounted 8 feet above the roof line and I can her the mobiles pretty clear

 

[CZ]

I live about 100 yards from a major freeway in Fresno County, and even the "extenders" are nearly impossible to hear.
No reception of cars on either the 785D, or246T from apartment with stock antennas, OR a antenna set in the window that I can see cars going by on on the Freeway from.

NO outdoor antennas allowed, so can't put anything outdoors.

 

[Tweekerbob]

CZ,

Try the antenna I mentioned in my previous post. I didn't mention that I heard 11 out of the 13 CHP frequencies with the antenna in my trunk laying flat! I forgot that I pulled it off the trunk and put it in the trunk when I started my "experiment". Try putting that antenna in the window and see if that helps.

Keep in mind that the CHP extenders use somewhere around a watt (I think it's less) for their extenders. Typically they are fed into a 5/8 wave antenna, so the ERP is around 1.5-2 watts. Point is, the signal is not very strong unless they are very close to you, maybe within a mile.

It would be bonus time if you have a balcony/porch that faces the freeway too! The antenna I mentioned is only 2 feet tall so no one will see it. Place it as high as you can (I don't think that anyone would question it if they saw up to 6-10" of it) in that porch area and run the coax in through a window. This is temporary enough to set it up and take it down within a minute or two.

HTH,

Ryan

 

[ssmith39]

Good CHP radio reference

See http://www.mbay.net/~wb6nvh/chpradio.htm.

Mobiles are repeated in the San Mateo county area. Makes listening to the CHP a pleasure. I am using a RS Discone feeding a PCR1000 with good results.

There is some speculation that the CHP may be buying new radios (I would imagine the the Rangr mobiles are getting elderly).

Mentioned in the site above, CHP has done some tests with the Kenwood product line.

 

[OpSec]

The current CHP mobile radio, the GE Rangr with S815 control head, was made specifically for CHP based on a contract with GE back in 1988. The firmware that controls the radio operation is custom to CHP. They were so popular that GE marketed a generic version to public safety and sold a lot of them with the similar S285 control head. That said, they are 17 years old and getting wore out. None of the major componets are made anymore, and CHP is being forced to beg/borrow/steal/part out radios to keep the fleet operational.

As Geoff Fors' page mentions, they switched from the fender-mounted fullsize 1/4w ball mount antenna to the rooftop base-loaded 1/4w NMO antenna in 1998 because of interference concerns with the new laptops in the cars.

The mobile repeaters ("extender" in CHP-ese) are ancient GE Mastr-Executive II's that have been around since the Micor days. I've got an operational Rangr/Mastr Exec II setup in my former Missouri HP car, and it's a solid platform that works great. The CHP extenders have a transmit power of a few 100 milliwatts, into the glass mount VHF antenna on the center of the rear window.

In order to listen to CHP effectively in a mobile scanner application you need to use a 1/4w ball mount or a base loaded NMO antenna like the lowband Antenex they use, or something like a Larsen NMO50 (even an NMO150 for VHF-Hi works great as a 30-50 MHz antenna) or MaxRad lowband antenna.

For a home application the coax dipole is great, but you need to have enough antenna in the air to capture the longer wavelength signal. Some people use the mutliband Comet/Diamond ham antennas that cover 6m/2m/70cm or even a commercial lowband folded dipole.

As for the replacement for the Rangr's, it looks like Kenwood is out front in the running with the TK-x90 series radio. I foresee CHP equipping their cars with more than just the lowband radio, since the need for mutual aid comms is readily apparent in a state so big. They could probably get a sweet deal from Kenwood for an x90 system that has lowband and highband VHF drawers with dual contol heads that take up the same room as the huge S815 heads now. My only question is how they will control the lights/siren, since the Kenwood has no interface to the Federal Signal equipment like the GE does.

The Visteon Corporation (a dvision of Ford) has an intergrated computerized system that CHP is testing, but it costs bucko $$ and is very complicated...it combines the 2-way radios, MDC, emergency equipment, radar, scanner, in-car camera and who knows what else into a single user interface in the car. Personally, I think it makes the car into a video game and I wonder how it performs in the real world during Code 3 driving or other stressful events.

If you look at the interactive demo on the site, you'll see the screen shots are cleary of the CHP system.

http://www.evisteon.com/prod_serv/tacnet/index.shtml

Here is a trunk photo of the Visteon system, as viewed on the Police Car Web Site that was taken by "rwcar4" (http://www.geocities.com/policecarsite/). I added the red boxes and text.

 

[RolnCode3]

That's funny. It had an "AM/FM" button. Are they going to put stereos back in the patrol cars?