California Highway Patrol scanner info

Discussion in 'CB & Scanner Discussion' started by OpenRoad, Nov 29, 2014.

  1. OpenRoad

    OpenRoad Must go faster Advanced User Premium Member

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    I've put together a bit of info on scanning for California Highway Patrol, for those that are interested.

    Programming for CHP is easy, they use single frequency analog in the 42 mhz range (as opposed to trunking systems which use banks of frequencies and talkgroups). To get the most out of mobile scanning CHP, you need a 49 inch whip, like this one.

    CHP splits channels into pairs, Mobile and Base (dispatch). Mobile units always transmit on the M channel, and receive on the B channel, and of course dispatch is the flip side of that, receiving M frequency and transmitting B.
    A series of localized repeaters are used throughout the system, the more difficult the terrain, the more densely packed the repeaters. Mobile units transmit around 100 watts.

    CHP almost always (99% of the time) simulcasts the mobile radio traffic over the Base channel, so when you are scanning, you need only program the B channel and hear both sides of the conversation. The simulcast of mobile radio traffic is a safety feature in case dispatch goes away, that all mobile units can hear one another, even if they are in different areas. (I heard this happen twice now, where dispatch was MIA for the better part of an hour, with some sort of equipment problem, but mobile units could hear one another over the simulcast).

    The other thing that occurs, is that the mobile simulcast is re-transmitted on all local repeaters. In flat terrain like the central valley, Los Angeles, SF Bay Area counties, you typically hear crisp reception for both mobile and base. In other areas where the dispatch zone covers mountainous areas, like the coastal hills, Sierra Nevada, you typically hear all mobile units clearly, but dispatch may be scratchy or not heard at all for all conversations. What happens is that the radio system chooses the closest repeater to the sender, based on signal strength received from the mobile unit. So when the dispatch is talking to a unit, it is only transmitting on the single repeater that is closest to that unit. If you are on the other side of the mountain, or too far away from that repeater, you will not hear, or hear scratchy dispatch calls - but only when dispatch is communicating with a distant unit. Because the MOBILE traffic is simulcast on all repeaters, you will hear the distant mobile unit as if he were next to you. If a mobile unit is within a few miles of you, or reasonably close, then when dispatch is communicating with that unit, you'll be getting clearer reception since the repeater chosen will be close to you.

    It's an odd system for sure, because the dispatcher might be talking to a lot of units, and you'll hear her/him clearly one second, then scratchy or not at all the next, due to this ping-pong of repeaters being active and not - again only for the base channels.

    Because CHP also use CTCSS tone frequencies, you can dial squelch to zero, as the (assuming you have a radio that can program the tone) radio will auto-squelch when the transmission ends.

    For car-to-car, the mobile units transmit low power (5 watts) on the BASE channel. Since dispatch is listening only on the M channel, they will not hear any low power base traffic (there are special cases to this, but mostly). In order to hear car-to-car, you need to be physically near them, within 1 or 2 miles, since none of these transmissions will be broadcast on the repeaters.

    I've not covered digital extenders, since they are not much use for mobile scanning as the base channel always simulcasts anyway, its a wasted effort IMHO to try and snag the close digital extender transmissions. Digital extenders may or may not be in use on a traffic stop.

    http://www.wb6nvh.com/CHP2001.htm
    CVANT2010.jpg


    From radioreference for CHP, Monterey Dispatch Center. Note the 'color' names given by CHP, which are paired mobile-base frequencies. These same pairs exist in other areas in the state, but spread far enough away to avoid interference. Monterey itself contains 2 pairs for 2 geographically different areas, but are served from the same physical dispatch center. In this example, the Black "channel" covers an area contained within the Monterey County, while the Green channel covers Santa Cruz County, and the southern half of Santa Clara County and northern San Benito County.

    chp.png
     
    Last edited: Nov 29, 2014
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  2. OpenRoad

    OpenRoad Must go faster Advanced User Premium Member

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    Other references:

    http://wiki.radioreference.com/index.php/Department_of_the_Highway_Patrol_%28CHP%29_%28CA%29

    http://www.chp.ca.gov/prog/emailCCP.cgi

    http://www.freqofnature.com/index.php?m=California&p=Cal%20Highway%20Patrol

    http://www.radioreference.com/apps/db/?aid=995

    Also note when using radioreference, a lot of the 'extra' channels that are not paired M+B sets, you can ignore them. I've had many of them on my scanner, and have yet to hear a peep. So to avoid scanning nothing, just leave them out.
     
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  3. andresg

    andresg What is PSL? Advanced User Premium Member

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    I wonder if TX state troopers use the same technology.
     
  4. ggarrett

    ggarrett Premium Member Advanced User Premium Member

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  5. OpenRoad

    OpenRoad Must go faster Advanced User Premium Member

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    CHP are upgrading their equipment, though not changing this basic scheme and using the same 42mhz radios. A program tag named "CHPERS" started 4 years ago supposedly upgrades repeaters, adds new repeaters.

    In addition (something I was not aware of) is that not all regions do the simulcasting, so they want to add that do the entire state. It also sounds like they will begin simulcasting the BASE (dispatch) channel to all repeaters, which would make life great for scanning, as you'll be able to hear clear reception of both ends of a conversation all the time. (There are few radio dead zones in very remote areas, I surmise the goal is to fix that as well).

    http://www.wb6nvh.com/2009rpt.pdf

    ---------- Post added at 02:01 PM ---------- Previous post was at 01:13 PM ----------

    btw, you CAN scan CHP using a handheld scanner with a reasonable antenna, like the Diamond RH77CA. It's not going to give you the range of an external whip, but when you are in a metro area, you're probably already close to a repeater.
     
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  6. Benji

    Benji Premium Member Advanced User Premium Member

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    If only Uniden would hurry the **** up and release Siren..... I'll buy a scanner and set it up at home as high as possible with an insane antennae.
     
  7. CRS123

    CRS123 Premium Member Intermediate User Premium Member

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    Very helpful information and nicely put together...thanks. Back in the day, I used to have my CB w/ single side band and linear amp, along with a scanner and my mobile ham radio. Your post makes me want to set up a good scanner for CHP.
    CRS
     
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  8. GTO_04

    GTO_04 Premium Member Advanced User Premium Member

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    I'll take monitoring a low band state police/highway patrol system ANY day of the week! Needless to say I am jealous.:cool: ISP used to be on VHF Lo and I miss that! When Ohio was on low band I could pick up their air enforcement planes 20 miles away with a stock antenna on my Bearcat!

    GTO_04
     
    Last edited: Nov 29, 2014
  9. OpenRoad

    OpenRoad Must go faster Advanced User Premium Member

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    With height I can hear them really far away. When I am coming down out of the Sierra on I-80 overlooking the Central Valley at around 3500 feet elevation, I can hear the Golden Gate Dispatch channels, which are another 100 miles away.
     
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  10. NPark

    NPark -NNJCTG- Rollin', windows down, music up Advanced User Acceptus Premium Member

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    Good write-up OR! Very well said.


    Sent from my iPhone using Tapatalk
     
  11. OpenRoad

    OpenRoad Must go faster Advanced User Premium Member

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    LOL, from 3 years ago, but still valid.
     
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  12. NPark

    NPark -NNJCTG- Rollin', windows down, music up Advanced User Acceptus Premium Member

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    Maybe old, but I bet their system is still the same.


    Sent from my iPhone using Tapatalk
     
  13. Tregar

    Tregar Premium Member Beginner User Premium Member

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    Is there a distinct advantage of having an actual scanner over using an app like Scanner Radio (assuming cell service is not an issue) for CHP?
     
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  14. fitz4321

    fitz4321 Running With Scissors Advanced User Premium Member

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    I do t know the answer as far as function, but I’d say the advantage of the app is less scrutinization by an officer if you are pulled over. There would be no “why do you need a scanner” conversation.
     
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  15. GTO_04

    GTO_04 Premium Member Advanced User Premium Member

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    Yes, there are distinct advantages. You get the radio traffic in real time without any delay. With apps there is often a lag time, and it may be significant. The biggest advantage is that with a scanner, you get to pick which LE agencies you want to monitor. I can't get an app around here that lets me listen to what LE agencies I want to monitor.

    I have a ham license so I am legal to carry a scanner. Even if you're not it is still not much of an issue IMHO. If you're a "professional speeder" like most of us here :), you know when a LEO is coming after you. There is plenty of time to stash your handheld scanner under the seat or pull a jacket over it before he gets right behind you.

    GTO_04
     
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  16. Tregar

    Tregar Premium Member Beginner User Premium Member

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    If you had to estimate this is it longer than a minute? I had thought I needed a 42" antenna in order to run a scanner for CHP which I'm personally not ready to install onto my car. I'm not opposed to getting an amateur radio license though.
     
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  17. GTO_04

    GTO_04 Premium Member Advanced User Premium Member

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    Yes. Scanners are legal in CA no ham license required IIRC. While you will get better reception with a 42" whip, there are antennas you can place in the back windshield that will work very well. When Ohio Highway Patrol used VHF-Lo for air enforcement, I could pick them up 10 miles out with the stock antenna on my handheld Bearcat scanner.

    GTO_04
     
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  18. Tregar

    Tregar Premium Member Beginner User Premium Member

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    So I'm currently planning to use the app for now to see how I like using a scanner, but assuming I do decide to make the jump I'd be getting the antenna you linked me to and either looking at a BC125AT for a handheld analog scanner just for CHP or if I wanted to just go whole hog a BCD996P2 which it's understanding would allow me to scan fire/ems.
     
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