Hearing only one side of CHP

Status
Not open for further replies.

Gbcue

Member
Joined
Apr 8, 2008
Messages
139
Location
CA
I think I remember something about this, but I can only hear one side of CHP conversations, mostly only dispatch, even though I'm scanning every frequency in the database.

Does the dispatch not repeat out car transmissions?

Thanks!
 

1979lee

Member
Joined
Jun 24, 2005
Messages
368
Location
bakersfield, california
A Beginner's Guide to the CHP Radio System:
The CHP employs two frequencies for communications between units in the field and their dispatch centers. One frequency is used by base stations, located at electronic sites, most of which are placed on mountain peaks or other high positions. Cars, or mobile units, use a second frequency to talk with these base stations. On the list below the base frequency is shown as the "frequency" and the mobile frequency is shown as "input." It is important to realize that base stations transmit from higher elevations and at much greater power than mobile units do. For this reason the base frequency can be heard over long distances, while the lower powered ground level mobile units can only be received if they are close by. The dispatch centers use one or more electronic sites to communicate with mobile units. Remember that high locations are ideal for radio reception as they can "see" more territory than ground level sites. This is why the dispatcher can receive most of the mobile traffic, while the scanner listener cannot. Electronic sites are linked via microwave or 72 MHz frequencies and the dispatcher's console is controlled by a type of computer that chooses the best signal to send to the dispatcher if more than one site is receiving a mobile unit's signal at the same time. This computer is called a voter, as the selection among multiple sites is "voted" for the best signal. When transmitting to a mobile unit the dispatcher can choose the electronic site they want to use, and normally choose the same site the voter chose when replying to a mobile unit. This is why you may hear the base frequency come in well at times when a nearby site is being used and not so well when another, more distant site is being used. When units want to communicate directly with each other, commonly referred to as "direct" or "car to car", they both switch their radios to another channel where the radio is both receiving and transmitting on the base frequency. One disadvantage to this is the cars can have the same experience that scanner listeners have, which is that they cannot hear other mobile units that are located some distance away.

In some locations within the state, mostly in urban areas, and mostly in southern California, the mobile frequency is patched to the base frequency on the most often used electronic site within a dispatch area. Cars are now able to hear each other from longer distances that they could before. This works the best in dispatch areas that are small and mostly urban as in these areas most mobile units can receive the same electronic site. In rural areas the dispatch area can be quite large with as many as 6-12 sites and mobile units may only be in range of one of those sites. Since the advantage of having the other mobile units hear each other is lost, the mobile traffic is not transmitted over the base frequency in rural areas.

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

Mick

Member
Joined
Dec 19, 2002
Messages
2,475
Location
Western U.S.
Both mobiles and mountain tops are licensed for 100 watts in most locations. It's the height of the dispatch transmitter primarily that makes it easy for a scanner to hear them.

It is important to realize that base stations transmit from higher elevations and at much greater power than mobile units do.
 

ridgescan

Member
Joined
Apr 1, 2008
Messages
4,669
Location
San Francisco, Ca.
A Beginner's Guide to the CHP Radio System:
The CHP employs two frequencies for communications between units in the field and their dispatch centers. One frequency is used by base stations, located at electronic sites, most of which are placed on mountain peaks or other high positions. Cars, or mobile units, use a second frequency to talk with these base stations. On the list below the base frequency is shown as the "frequency" and the mobile frequency is shown as "input." It is important to realize that base stations transmit from higher elevations and at much greater power than mobile units do. For this reason the base frequency can be heard over long distances, while the lower powered ground level mobile units can only be received if they are close by. The dispatch centers use one or more electronic sites to communicate with mobile units. Remember that high locations are ideal for radio reception as they can "see" more territory than ground level sites. This is why the dispatcher can receive most of the mobile traffic, while the scanner listener cannot. Electronic sites are linked via microwave or 72 MHz frequencies and the dispatcher's console is controlled by a type of computer that chooses the best signal to send to the dispatcher if more than one site is receiving a mobile unit's signal at the same time. This computer is called a voter, as the selection among multiple sites is "voted" for the best signal. When transmitting to a mobile unit the dispatcher can choose the electronic site they want to use, and normally choose the same site the voter chose when replying to a mobile unit. This is why you may hear the base frequency come in well at times when a nearby site is being used and not so well when another, more distant site is being used. When units want to communicate directly with each other, commonly referred to as "direct" or "car to car", they both switch their radios to another channel where the radio is both receiving and transmitting on the base frequency. One disadvantage to this is the cars can have the same experience that scanner listeners have, which is that they cannot hear other mobile units that are located some distance away.

In some locations within the state, mostly in urban areas, and mostly in southern California, the mobile frequency is patched to the base frequency on the most often used electronic site within a dispatch area. Cars are now able to hear each other from longer distances that they could before. This works the best in dispatch areas that are small and mostly urban as in these areas most mobile units can receive the same electronic site. In rural areas the dispatch area can be quite large with as many as 6-12 sites and mobile units may only be in range of one of those sites. Since the advantage of having the other mobile units hear each other is lost, the mobile traffic is not transmitted over the base frequency in rural areas.

http://www.radioreference.com/apps/db/?aid=995
I wish there was rep to give you on this forum. Thank you much for that perfect explanation:) I was wondering about it too.
 

SCPD

QRT
Joined
Feb 24, 2001
Messages
0
Location
Virginia
So you say your located in santa rosa !
I do not have any prolem picking up mobile and base.
what frequency you listen to in Santa Rosa ?
From my house or when I'm local I can hear both mobile and dispatch.
I pick up napa with no problem then Marin comes in slightly stronger the Santa Rosa, also I can pick up from my home somewhat weak Oakland , howard
do you have any of the extender freq. programmind ?
 
Joined
Mar 24, 2006
Messages
55
Both mobiles and mountain tops are licensed for 100 watts in most locations. It's the height of the dispatch transmitter primarily that makes it easy for a scanner to hear them.

I remember studying "Transmitter Power Output X Height Above Average Terrain = Effective Radiated Power." It's the ERP that gives RF it's distance and since dispatch is higher than mobile, it has more ERP.
 

SCPD

QRT
Joined
Feb 24, 2001
Messages
0
Location
Virginia
Both mobiles and mountain tops are licensed for 100 watts in most locations. It's the height of the dispatch transmitter primarily that makes it easy for a scanner to hear them.

I remember studying "Transmitter Power Output X Height Above Average Terrain = Effective Radiated Power." It's the ERP that gives RF it's distance and since dispatch is higher than mobile, it has more ERP.
I just looked up a couple of the licenses for the remote bases in the eastern Sierra and most of them show an output power of 120 watts with the ERP the same with one exception. That one had an ERP of 190 watts with an output power of 120 watts. That location is probably not any higher above the average terrain than the rest, in fact, it is much less above the average terrain than at least one of the sites where the ERP and output power are shown the same in the license. The difference at that site must be in the antenna. That site (Pine Grove near Yerington, Nevada) may have a directional antenna and the gain might be picked up because of that.

On the statewide mobile license (KA4993) the output power and ERP are listed as 100 watts, so at least here in the eastern Sierra the remote base stations are more powerful.
 
Last edited:

Norman

Member
Joined
Dec 19, 2002
Messages
294
Location
N CA
You didn't say what kind of antenna you were using with your scanner. Maybe the telescoping one that came with it? To really hear the CHP, you will need an antenna that covers that part of the band (42 MHZ).
An omni ground plane with 3 or 4 long drooping radials will work just fine. Mount outside as high as practicable, and you should hear them quite well. Some base stations repeat the mobile units. Also, you should hear some on the extender freq of 154.905. Hope this helps.
Norm kc6zwt.
 

WayneH

Forums Veteran
Super Moderator
Joined
Dec 16, 2000
Messages
7,501
Location
Sitting in an airport somewhere
I remember studying "Transmitter Power Output X Height Above Average Terrain = Effective Radiated Power." It's the ERP that gives RF it's distance and since dispatch is higher than mobile, it has more ERP.
In context of licensing, ERP is the wattage in to the antenna with the antenna gain applied to it.

Dispatch centers receive and transmit directly from the radio site.
 

Harlute

Member
Joined
Dec 28, 2005
Messages
24
my two cents

I think the number one problem with people being able to hear CHP is using a poor antenna for low-band, or not having it in a good position.

On the CHP page in the RR database there is this paragraph or two about how the mobile CHP traffic is not repeated. Well it SURELY is in the Chico Dispatch center and the five counties served (all of the time, it seems). Yes, the dispatcher has remote transmitters available and that is what they primarily use, however, if you have a good enough antenna, or are close enough to the repeater, you only need to listen to one frequency to hear all of the traffic.

I used to never be able to hear anything but the dispatcher and I even posted about it some time ago; I can now hear all of it.
 
Last edited:

Sac916

Member
Joined
Dec 19, 2002
Messages
1,402
Well, I'm usually mobile when I'm listening to the CHP...
You'll hear a world of difference with an Antenex antenna like this
( example ony - I have never shopped wpsantennas.com )

http://www.wpsantennas.com/browsepr...(40-47MHz--Unity-Gain--49--Tapered-Whip).html

Also need NMO magnet mount with BNC connection like this....

http://cgi.ebay.com/Tram-NMO-Magnet...VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247

ebay item # 220147331867

With those two items you'll hear a TREMENDOUS difference while driving around town. It's not descrete, it'll scape the roofs of many fast food joints and you can't go through a car wash - but it works nicely.

It'll work well with 150MHz, 450MHz and other bands simply because it's a big antenna mounted outside, but you'll see the biggest improvement with CHP 40MHz freqs.
 

WayneH

Forums Veteran
Super Moderator
Joined
Dec 16, 2000
Messages
7,501
Location
Sitting in an airport somewhere
On the CHP page in the RR database there is this paragraph or two about how the mobile CHP traffic is not repeated.
In context it is technically not repeated in the traditional sense. The mobile audio is the audio the dispatch center receives and is then rerouted back to the site and retransmitted.

This is versus it being immediately retransmitted at the site like a traditional repeater.
 

WX5JCH

Completely Banned for the Greater Good
Banned
Joined
Dec 7, 2004
Messages
941
Location
Elk City, Oklahoma
I heard CHP gold just fine the other morning. From here in Oklahoma. Good skip conditions I assume.
 

gmclam

Member
Premium Subscriber
Joined
Sep 15, 2006
Messages
5,700
Location
Fair Oaks, CA
Isn't low band VHF more fun?

I heard CHP gold just fine the other morning. From here in Oklahoma. Good skip conditions I assume.
Are you sure it is not CHP Bronze? Yeah the skip can be wild sometimes as I've been able to hear CHP with CT of 107.2 while in southern California, and CHP with CT of 131.8 while in northern California.
 

gmclam

Member
Premium Subscriber
Joined
Sep 15, 2006
Messages
5,700
Location
Fair Oaks, CA
CHP channel confusion

and CHP Gold in nor cal valley is pl of 179.9
Uh huh. And CHP GOLD BASE in other parts of the state can be 118.8, 162.2 or 192.8. But if the CT is 131.8, then the same frequency is called BRONZE BASE. The mobile frequency also uses 118.8, 179.9 & 192.8 for GOLD MOBILE, but 131.8 is EMERALD MOBILE. And if 162.2 then it is GOLD 1 MOBILE.

So when talking about CHP channels, it is fairly important to include the CT (and frequency) in order to be sure of the correct channel.
 

FmrNYkr

Member
Premium Subscriber
Joined
May 3, 2008
Messages
26
Location
S.F Bay Area
Can't hear Oakland Dispatch, but hear mobile units 5X5

I'm in the Oakland Hills and with my BC785D, I can hear San Francisco, San Jose, Redwood City and Marin dispatch and with two way traffic in most instances. My problem is I cannot receive Oakland dispatch but can hear the mobile units 5X5. I have an antenna hanging in the window, with a clear shot to the south west with a line of sight to Twin Peaks.

Any ideas or people with the same problem?

Tnx,

FmrNYkr
 
Status
Not open for further replies.
Top