How come i only get one side of CHP conversations?

[mattfox27]

I'm in Los Angeles i programmed CHP from database, how come i only hear one side of the conversation?

[Mick]

In L.A. County the CHP has duplex channels for each office. You hear the dispatcher on one channel, the mobile unit on another channel.

Go to http://www.radioreference.com/apps/d...1&aid=995#cats
and then click on Frequency Display Options to have it show "Input Frequencies" (this is such a hassle) then go to Southern Division for the L.A. County CHP frqs.

Originally Posted by mattfox27

I'm in Los Angeles i programmed CHP from database, how come i only hear one side of the conversation?

[mattfox27]

So how do you listen to them? You have to keep switching back and forth?

[Delldell26]

Program them in and hit scan ;-)

[gmclam]

Originally Posted by mattfox27

So how do you listen to them? You have to keep switching back and forth?

Yes. Not only do you have to switch back and forth between the two frequencies, you need a VERY GOOD low band VHF antenna (or be in an awesome location) to pick up the cars.

I have several tricks for listening to CHP. One is to dedicate one scanner for just this purpose. If you only want to hear one channel (two frequencies) set the delays to OFF. I you want to hear more than one channel, you might have to keep hitting scan to get back to the conversation you just heard the first half of. Another thing I sometimes do is to put one of the two frequencies into the PRIORITY channel and leave the scanner in MAN mode and parked on the other (again only works with one channel). But none of that matters if you do not have a good enough signal to pick up the cars.

[ac7xc]

Originally Posted by mattfox27

I'm in Los Angeles i programmed CHP from database, how come i only hear one side of the conversation?

The CHP uses two channels. One for base and one for mobiles. You need a good and high antenna for VHF-Lo. If you have a good antenna then considering buying a dedicated scanner for VHF-Lo to monitor the CHP. Since VHF-Lo requires no trunking or digital modulation decoding scanners that cover this band are cheap and plentiful. When I lived in CA I made sure the delay was off so that I could hear the base and mobile stations without any cutting out.
CHP mobiles use mobile extenders also in the VHF-Hi band so you can also program that into your scanner to hear close by hand held and mobile communications. This is the freq used by mobile extenders
154.905

Here is the CHP page at radioreference.com:
http://www.radioreference.com/apps/db/?aid=995

[KMA367]

Agree completely with "gmclam." Unless (or perhaps I should say until) CHP puts their L.A. area channels on repeaters, hearing the mobiles will remain difficult and all but impossible without your having a first-rate low-band antenna in a first-rate, high-elevation location. It's been that way since they took over the Los Angeles freeways in 1968-69, and it's something we've just had to adjust to for these 40 years. And in most of the state the problem is the same.

CHP's dispatchers can, of course, hear their cars, which is the goal of their or any radio system, and we scanner listeners' preferences are no doubt way down on their list of things to do. Probably not even on it. Having said all that, they do have grand plans for major modifications of their radio system statewide over the next several years, so eventually we may get what we've been waiting for.

Your question, mattfox27, is probably the one most common one that comes up repeatedly (so to speak ) in the California forum, for the many areas of the state in which CHP isn't repeated. Maybe there should be a wiki or a sticky for this right up at the top of the CA Forum page. Or a link to the one or more pages on and off RR which discuss the issue.

As an aside, gmclam's technique of using a second, dedicated receiver and or the PRIORITY function can also be useful for hearing LASD mobiles, whose transmissions are almost always covered by their age-old "busy-beeps." But again, you need a good antenna (UHF in their case) and a good location to do it. And since many if not most of their units' transmissions are from their HTs, they're usually only putting out 2- or 5-watt signals, which makes your proximity to the mobiles even more important than with the CHP's higher powered low-band signals.

Originally Posted by gmclam

Yes. Not only do you have to switch back and forth between the two frequencies, you need a VERY GOOD low band VHF antenna (or be in an awesome location) to pick up the cars.

I have several tricks for listening to CHP. One is to dedicate one scanner for just this purpose. If you only want to hear one channel (two frequencies) set the delays to OFF. I you want to hear more than one channel, you might have to keep hitting scan to get back to the conversation you just heard the first half of. Another thing I sometimes do is to put one of the two frequencies into the PRIORITY channel and leave the scanner in MAN mode and parked on the other (again only works with one channel). But none of that matters if you do not have a good enough signal to pick up the cars.

[drsl2000]

Originally Posted by mattfox27

I'm in Los Angeles i programmed CHP from database, how come i only hear one side of the conversation?

The data base is in error for a lot of the CHP. In this regard, I submitted two database updates for LA CHP, noting that the sites erroneously show as repeated(R). My submissions are "complete". However, the database for LA CHP is still in errorr and are shown as repeated.

[brandon]

You can also scan the 72 or 75 MHz range (in some areas) to pick them up. I used to do this in the old days before the San Diego CHP offices switched to 39 MHz repeaters.

[gmclam]

Originally Posted by drsl2000

The data base is in error for a lot of the CHP. In this regard, I submitted two database updates for LA CHP, noting that the sites erroneously show as repeated(R). My submissions are "complete". However, the database for LA CHP is still in errorr and are shown as repeated.

I can understand that most people could care less about "input frequencies". However, considering how the CHP system really works, I don't think cars should be listed as input frequencies. There should be TWO entries for each channel; for example:

42.12000 KDE678 BM179.9 PLGOLD North Sacramento Office FM Law Dispatch
42.20000 KDE678 BM179.9 PLGOLD North Sacramento Mobiles FM Law Dispatch

[KMA367]

Originally Posted by gmclam

I can understand that most people could care less about "input frequencies". However, considering how the CHP system really works, I don't think cars should be listed as input frequencies. There should be TWO entries for each channel; for example:

42.12000 KDE678 BM179.9 PLGOLD North Sacramento Office FM Law Dispatch
42.20000 KDE678 BM179.9 PLGOLD North Sacramento Mobiles FM Law Dispatch

Excellent idea, IMHO.

The only tweak I'd suggest is that the "base" side be listed as "North Sacramento Dispatcher" (rather than 'Office", since they're not really dispatched from the office). The mobile side would be fine just as you have it

Good thinking, and the only change to the "standard' freq display in the database would be that for CHP there would be little need or use for the "Frequency Display Options (Input Frequencies Shown/Hidden)" dropdown.

[Mike_G_D]

All of which is why I still maintain that the scanner manufacturers should add a duplex-specific channel feature to their units. With the proliferation of multi-frequency trunking systems the association of "channel" with only one specific frequency as in the old pre-trunking scanner days is no longer fixed in stone. It is obvious that they have essentially nailed multi-frequency systems so why not do the same with a simple two-frequency duplex system?! I envision the GRE version of this as a "DSYS" (Duplex SYStem) to go along with the current TSYS (Trunking SYStem) options. It would simply be a channel which contains two frequencies. When the unit scans that "channel" it listens on both of the assigned frequencies (scans rapidly between the two) for a user set time delay and will unsquelch on receipt of a signal on either frequency. There would be no delay, of course, for each frequency so as to allow rapid switching between the two during a normal conversation, only an overall channel delay (user set and/or a default just as in normal simplex/repeater conventional channels) for the duplex channel. From a user perspective, the channel would seem to be no different from any other single frequency conventional channel. Of course this doesn't assuage the need for a decent antenna and location but it greatly simplifies the programming and reception of such two-frequency systems especially when you have multiple two-frequency channels programmed!

-Mike

[cousinkix1953]

Originally Posted by brandon

You can also scan the 72 or 75 MHz range (in some areas) to pick them up. I used to do this in the old days before the San Diego CHP offices switched to 39 MHz repeaters.

You can do the same thing in Monterey county. The black mobile 42.70 is repeated on 72.24 mhz.

The San Jose office used to have a mobile link on 900 mhz. It was replaced by a repeater; so both sides of the conversation is heard on 42.50 mhz and miles beyond their coverage area. Sometimes it is also simulcast on 453.825 mhz. You don't even need low band receivers or antennas.

Most of the state is still stuck trying to deal with an obsolete duplex system stuck on a skip infested low band. I just don't pay much attention to them any more...

[Exsmokey]

Keep in mind that the 72 MHz frequencies are links between two fixed points. Each point has a vertically polarized antenna so the path is relatively narrow. Before it was removed I could pick up a 72 MHz link from 40 miles distant that was aimed about 160 degrees in the other direction. This in mountainous terrain. My antenna is quite good and was essential for receiving this signal. Your results may vary!

This link was removed when the CHP managed to put in enough solar power to add the site to the state's microwave network.

When I received my GRE-600 I was disappointed to see that it did not include the 72 MHz range. Although there are a limited number of links in the 72 MHz area, they can come in quite handy in a number of places.

I like the idea Mike put forth. I don't see it happening, unfortunately, because there are fewer of these types of systems than there used to be.

Finally, I wish the administrators of this site would add an explanation of the CHP's system in a sticky thread. This is probably the most often asked question in the California forum. Beginners with this question don't always look at the database when they find they can't hear the mobile side. They may see a sticky thread more often. I like the idea of showing the CHP differently as well. Many folks don't choose to change from the default setting of not showing "input" frequencies.

[Chauffeur6]

The NYSP suffers from the same terrible problem in the database. They also use a duplex system with the base transmitting CSQ, while the mobiles use differing PL's based on zones within each Troop. Unfortunately, they are listed as if they are repeaters, with the mobiles listed as "input" with the PL. So what happens is, someone unfamiliar with the way they operate will wind up with what looks like a repeater output with PL, and they'll never hear a thing!

The entries really ought to be broken down and listed exactly as gmclam illustrates, separate entries for the base and mobiles. It's the only way to ensure people will enter both frequencies with the proper PL/DPL tones (or lack thereof)

[gmclam]

Originally Posted by Exsmokey

When I received my GRE-600 I was disappointed to see that it did not include the 72 MHz range.

I just got a PSR-300 which is an analog scanner and has 700 MHz capability, but not 72 MHz. GRE's "logic" escapes me.

I like the idea Mike put forth. I don't see it happening, unfortunately, because there are fewer of these types of systems than there used to be

I have scanners that I modified in the 1970s (added CPUs to PRO-77s/etc) which do this. I plan to put one online in a couple of weeks.

Finally, I wish the administrators of this site would add an explanation of the CHP's system in a sticky thread.

There is an explanation of this at the top of the page when you select "CHP" from the DB. The problem is that people are using the IMPORT function of their software and no longer accessing the DB via human means. Stickies are just as easily overlooked.

I like the idea of showing the CHP differently as well. Many folks don't choose to change from the default setting of not showing "input" frequencies.

I understand that either people don't want to see the input frequencies, or are confused when they are shown. I never liked the change where they now have to be "selected". I check in here a lot and don't want to always have to log in to get my default setting that shows them.

More importantly however; the CHP channels DO NOT USE INPUTs!!!! They are a full duplex channel using two separate frequencies. Showing each frequency with an input it TOTALLY INCORRECT.

[Chauffeur6]

Originally Posted by gmclam

More importantly however; the CHP channels DO NOT USE INPUTs!!!! They are a full duplex channel using two separate frequencies. Showing each frequency with an input it TOTALLY INCORRECT.

Something has got to be done with both the CHP and NYSP systems to address this issue. I'm quite sure they're not the only two duplex systems in the RR database that are essentially incorrectly listed as if they were repeaters. I'm not sure about the CHP system, but this problem is even more glaring with the NYSP given that the base transmits SQL while the zone patrols transmit back with three or more unique PL's. Anyone entering or importing the NYSP system, and not having the knowledge of how it works or how to correct the entries, would literally hear nothing if they have a scanner with PL enabled. Even without PL enabled, they would still only hear the base, which is the same issue with the CHP system as it stands now.

This current entry:

Troop F (Middletown)
155.53500 154.93500 BM 127.3 PL F ZONE 1 Dispatch FM Law Dispatch
155.53500 154.93500 BM 146.2 PL F ZONE 2 Dispatch FM Law Dispatch
155.53500 154.93500 BM 167.9 PL F ZONE 3 Dispatch FM Law Dispatch
155.53500 154.93500 BM 110.9 PL F TROOP Dispatch - Non-NYSP units FM Law Dispatch


Really needs to be listed as such for it to make sense and work properly:

Troop F (Middletown)
155.53500 B CSQ F TROOP Base to Mobiles FM Law Dispatch
154.93500 M 127.3 PL F ZONE 1 Mobiles to Base FM Law Dispatch
154.93500 M 146.2 PL F ZONE 2 Mobiles to Base FM Law Dispatch
154.93500 M 167.9 PL F ZONE 3 Mobiles to Base FM Law Dispatch
154.93500 M 110.9 PL F TROOP Mobiles to Base (Non-NYSP units) FM Law Dispatch