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

    Messages:
    14,412
    Likes Received:
    11,944
    Country:
    United States
    Joined:
    May 17, 2011
    Location:
    Surf City ---------------> Santa Cruz <-------
    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.


    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.
     
    Last edited: Nov 29, 2014
    NPark, K2theFEA, BrownOut and 12 others like this.
  2. OpenRoad

    OpenRoad Must go faster Advanced User Premium Member

    Messages:
    14,412
    Likes Received:
    11,944
    Country:
    United States
    Joined:
    May 17, 2011
    Location:
    Surf City ---------------> Santa Cruz <-------
    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.
     
    Last edited: Nov 29, 2014
    NPark, BrownOut, GTO_04 and 3 others like this.
  3. andresg

    andresg What is PSL? Advanced User Premium Member

    Messages:
    5,356
    Likes Received:
    3,574
    Country:
    United States
    Joined:
    Nov 28, 2013
    Location:
    San Antonio, TX.
    I wonder if TX state troopers use the same technology.
     
  4. ggarrett

    ggarrett Premium Member Advanced User Premium Member

    Messages:
    1,124
    Likes Received:
    927
    Joined:
    May 24, 2013
    Location:
    NC
    Last edited by a moderator: Nov 29, 2014
    Benji, OpenRoad and andresg like this.
  5. OpenRoad

    OpenRoad Must go faster Advanced User Premium Member

    Messages:
    14,412
    Likes Received:
    11,944
    Country:
    United States
    Joined:
    May 17, 2011
    Location:
    Surf City ---------------> Santa Cruz <-------
    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.
     
    GTO_04 likes this.
  6. Benji

    Benji Premium Member Advanced User Premium Member

    Messages:
    4,596
    Likes Received:
    2,358
    Country:
    United States
    Joined:
    Mar 17, 2012
    Location:
    San Antonio, TX.
    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

    Messages:
    630
    Likes Received:
    459
    Country:
    United States
    Joined:
    Nov 27, 2013
    Location:
    California
    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
     
    OpenRoad likes this.
  8. GTO_04

    GTO_04 Premium Member Advanced User Premium Member

    Messages:
    3,390
    Likes Received:
    2,608
    Country:
    United States
    Joined:
    May 21, 2011
    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

    Messages:
    14,412
    Likes Received:
    11,944
    Country:
    United States
    Joined:
    May 17, 2011
    Location:
    Surf City ---------------> Santa Cruz <-------
    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.
     
    K2theFEA and GTO_04 like this.
  10. NPark

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

    Messages:
    5,687
    Likes Received:
    5,299
    Country:
    United States
    Joined:
    Nov 10, 2015
    Location:
    Northern NJ
    Good write-up OR! Very well said.


    Sent from my iPhone using Tapatalk
     
  11. OpenRoad

    OpenRoad Must go faster Advanced User Premium Member

    Messages:
    14,412
    Likes Received:
    11,944
    Country:
    United States
    Joined:
    May 17, 2011
    Location:
    Surf City ---------------> Santa Cruz <-------
    LOL, from 3 years ago, but still valid.
     
    NPark likes this.
  12. NPark

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

    Messages:
    5,687
    Likes Received:
    5,299
    Country:
    United States
    Joined:
    Nov 10, 2015
    Location:
    Northern NJ
    Maybe old, but I bet their system is still the same.


    Sent from my iPhone using Tapatalk
     

Currently Active Users Viewing This Thread: 0 (Users: 0, Guests: 0)