Can Barely Hear California Highway Patrol (Low Band)

[zz0468]

Simulcasting is attractive for scanner listeners, but has little utility for the CHP. Aside from problems keeping transmitters synchronized there is no need for all cars to hear all transmissions.

What problems synchronizing transmitters? GPS disciplined reference sources are quite affordable, and modern transmission equipment (microwave radios, multiplexers, etc.) are extremely stable.

Having been involved in engineering and maintenance of analog simulcast systems since the 1970's, I really don't understand the source of the myths that low band simulcast is difficult to get right. It's not.

Low band has plenty of other problems, but synchronizing transmitters is not one of them.

The need is simple... a large coverage area with a single common channel. It's a spectrum conservation technique.

 

[uman18]

A year or two ago I noticed the same. Before you would hear everything off the simulcast system but it has been re-designed since they added a new frequency in the county and it's not simulcast anymore. (Ventura County)

 

[krazybob]

VHF low-band is unique because of the longer-wavelength. It bends around objects such as rock formations and trees and all the things that you would consider in a rural area. This is known as refraction. It has what is known as TDI. Signal distortion in simulcast overlap regions is referred to as time delay interference.

TDI occurs when two or more simulcast signals arrive at the user’s radio antenna with comparable amplitude and relatively large delay. Adding to this is you have "skip" interference on low band. Right now we're at the low of a very low sunspot cycle and it's not showing itself. But as we start climbing into the sunspot cycles high we will start hearing interference. When a sunspot cycle is high is when low band signals especially go up to the ionosphere and reflect back down at an equal but opposite angle. What this means is that you may hear Los Angeles CHP in Kansas City just fine but not in Los Angeles. Building antenna systems with sharp 90° nulls on low band is extremely difficult and in part because of this phenomenon. I still don't understand why CHP decided to go repeater simulcast.

The best I ever heard was when I was stationed as a military policeman in Germany. We were listening to a high speed chase somewhere in the south. I can only tell by the accent. We were only getting the officer side which suggested that it was a repeater. It was strong enough to match your cover our local traffic. Sure was a rip-roaring pursuit at 4:30 a.m. FRG time... and then it was just gone. That's the nature of skip interfering with VHF low-band.

As an amateur radio operator that works these bands I can tell you that you can have somebody 5 miles away on the other side of your town and you can have your beams pointed directly at one another and still you cannot hear one another. This effect or issue is not prevalent at VHF high band and above. It's very rare that you even have ducting.

This is to say that simulcasting on low band is not impossible as we already know from CHP. But it requires more in-depth attention such as making sure that the transmitters are exactly on frequency and firing off at exactly the same nanosecond as all other machines.

Sent from my SM-G965U using Tapatalk

 

[PCTEK]

As of today, I'm still not hearing any traffic from Golden Gate or Redwood City centers. Is there anyone with ties to the CHP Comm department that can determine if the voting system is down, or what else might be the change? This morning out of my office, I saw CHP stop all 101 north traffic. I had my scanner on and it heard nothing. I even had close call on and still nothing. Something has changed.. just trying to figure what... Thanks

 

[IcomIcR20]

Is California the last state to keep the low band

Sent from my moto e5 play using Tapatalk

Not really. Many rual Virginia police departments still make use of low band. Around here, some school buses, DOT, and a few other state agencies still use low band for some comms.

Some counties in PA were still using low band a while back when I caught a band opening that way. It is quickly being phased out, but low band is still in use in certain places. For instance, the plug was just pulled on the NC Highway Patrol low band network and is now full time 800 MHz trunking.

 

[krazybob]

Not really. Many rual Virginia police departments still make use of low band. Around here, some school buses, DOT, and a few other state agencies still use low band for some comms.

Some counties in PA were still using low band a while back when I caught a band opening that way. It is quickly being phased out, but low band is still in use in certain places. For instance, the plug was just pulled on the NC Highway Patrol low band network and is now full time 800 MHz trunking.

Our school district is one that still uses low band. From the altitude that we are at they have a tremendous distance so that when buses go down to Disneyland or various other places they can be picked up by the bay station loud and clear. Have a very similar range to my 2 meter repeater and perhaps even greater. California Department of Forestry known as CDF or Cal Fire still maintains an active license so numerous low-band frequencies that are still active just not used. I'm guessing that these your Fail-Safe frequencies as used by the state for interoperability somehow. I would only be guessing if I tried to figure it out.

The characteristics of skip as it's known are so pronounced that when we're in a good sunspot cycle I'm encouraged to put a 6 meter repeater up. What many repeaters Runners do on 6m is they turn off PL which allows stations that can hear the repeater to get into it. You would be surprised how many people around the country and around the world for that matter can get into your 6 meter repeater and hold a conversation. If this can be done in the amateur radio frequencies directly adjacent to Public Safety you know that Public Safety has an issue with signals that are doubling and in most cases are some cases taking out legitimate traffic the dispatcher has to try to figure out what's going on.

 

[IcomIcR20]

If this can be done in the amateur radio frequencies directly adjacent to Public Safety you know that Public Safety has an issue with signals that are doubling and in most cases are some cases taking out legitimate traffic the dispatcher has to try to figure out what's going on.

Thank goodness for PL tones

But yes, from here in NC, I once heard numerous loud VHF Low band signals from MD and PA using a tiny whip antenna from the middle of the house. Needless to say, that must have been some opening! And it was in the dead of winter when skip is rare.

 

[zz0468]

I still don't understand why CHP decided to go repeater simulcast.

You can probably infer the reasoning by the problems that particular type of system solves. Simulcast solves wide area coverage while conserving spectrum. A single RF frequency can talk out to a large area with reduced dead spots. You can do the same thing with multiple channels, but then you have large overlaps with similar coverage but on different frequencies, and with the skip potential of low band, you can interfere with many systems, not just a few. So, simulcast can make sense.

As for the repeater, that one is simple. Car to Car communications.

They clearly saw the benefit to their particular operation. One of the reasons it might sound bad to some folks is, they may be listening from outside the design coverage area. It might be strong signals there, but if the timing is off, it'll sound pretty cruddy.

 

[krazybob]

Thank goodness for PL tones

But yes, from here in NC, I once heard numerous loud VHF Low band signals from MD and PA using a tiny whip antenna from the middle of the house. Needless to say, that must have been some opening! And it was in the dead of winter when skip is rare.

You've just proving my point. How awesome to be listening on just the whip antenna on the back of the radio in here Los Angeles coming in. We were in patrol cars that had four and a half foot tall whip antennas on the back - about half the length of a CB radio antenna. Pretty cool! Could you tell which Los Angeles agency was coming in?

Sent from my SM-G965U using Tapatalk

 

[IcomIcR20]

You've just proving my point. How awesome to be listening on just the whip antenna on the back of the radio in here Los Angeles coming in. We were in patrol cars that had four and a half foot tall whip antennas on the back - about half the length of a CB radio antenna. Pretty cool! Could you tell which Los Angeles agency was coming in?

Sent from my SM-G965U using Tapatalk

I've never heard LA from all the way over here. It was PA and MD that I was hearing...

 

[krazybob]

I've never heard LA from all the way over here. It was PA and MD that I was hearing...

My apologies. I thought I was replying to somebody that mentioned they were hearing Los Angeles. None the less, from North Carolina you're still picking up Maryland and Pennsylvania. That's a common 6 meter opening in amateur radio. Short hauls of 500 miles or so. I have been a ham radio operator for more than 40 years and done a lot in that amount of time. Both private and Commercial.

Others are much greater. I recall once working a mobile in Kansas City and I was using a 10m antenna. I hadn't checked the switch position and loaded up just fine and held a 5-9 conversation with the mobile. My apologies for getting your details incorrect.

Sent from my SM-G965U using Tapatalk

 

[scottyhetzel]

Here in the Central Valley, they still use low band. I can get the pink, silver, blue and maroon with just an outside ST-22 antenna that is sitting on the ground. They do use multicast or simulcast, I am not sure what to call it to broadcast the mobiles. I have heard the Coalinga units on their new 700 MHZ from time to time.

It’s a vote steer system. Mobil’s hit certain repeater... based on what is closer.

 

[kg6nlw]

I've had little issues with a Kenwood TK690-H and a Larson NMO tuned to Lowband on the mobile. The house is the same but with a dedicated mountaintop site antenna at the house. I'm in the Golden Gate region.

Regards,

-Frank C.

 

[dhalbasch]

As of today, I'm still not hearing any traffic from Golden Gate or Redwood City centers. Is there anyone with ties to the CHP Comm department that can determine if the voting system is down, or what else might be the change? This morning out of my office, I saw CHP stop all 101 north traffic. I had my scanner on and it heard nothing. I even had close call on and still nothing. Something has changed.. just trying to figure what... Thanks

What tone are you using?

 

[Oakland_Tower]

As of today, I'm still not hearing any traffic from Golden Gate or Redwood City centers. Is there anyone with ties to the CHP Comm department that can determine if the voting system is down, or what else might be the change? This morning out of my office, I saw CHP stop all 101 north traffic. I had my scanner on and it heard nothing. I even had close call on and still nothing. Something has changed.. just trying to figure what... Thanks

I just tuned in 42.08 and heard 91 units being simulcast. I only listened for a few minutes and it seemed the same site was being heard. So I can confirm the Redwood City office is still on 42.08. I should add this was heard from Fremont with a clear view of the peninsula.

 

[krazybob]

Others appear to be hearing traffic on the frequency and you are not. If you are using an outside antenna make sure that your cable is still good. If that's good try checking the various blue frequencies as well as the green frequencies. If there frequencies are under maintenance they will usually go to one of the blue repeaters for the duration. I don't monitor the green frequencies and thought that they were only simplex. But simplex from the base station when they're antenna 60 feet in the air would cover quite nicely. Just giving you options. I don't listen to the green frequencies at all.

Sent from my SM-G965U using Tapatalk

 

[Sshalita]

I can confirm that CHP Redwood City and San Jose are working on their regular frequencies. There has been no interruptions for the past two weeks.

Check your antenna cables. Also check if you might have programmed the wrong PL tone in error. I don’t use PL, but that would definitely block receiving transmissions if it’s wrong.

.

 

[PCTEK]

Looking out at Highway 101/92 in San Mateo, I see two CHP SUV's and 1 motorcycle unit with their lights on and several civilian cars pulled over. I switched on my scanner (Uniden 536HP) and I can hear their traffic to and from the Golden Gate center on.... the Extender 700MHz channels. I am hearing the "Black", "Turquoise", "Amber" and 1 other stations all using what RR lists as "700MHz Extender" channels. One is using the "VRS" channel. Perhaps CHP has moved off of low band (at least in my area San Mateo 101/92). Seems RR may need to update the data base??

 

[Oakland_Tower]

Please read the posts above. There is something wrong with your programming. They are still on 42.08. Perhaps you have the wrong CTCSS programmed. I would turn the CTCSS off and stop your scanner on 42.08 and have a listen. It is possible that your antenna will receive UHF much better than VHF low band...especially if it is indoors...but they are still on 42.08.

 

[6079smithw]

I80 over Donner was a mess for the past few days because of the weather and CHP Tahoe Grey2 was going full blast. I went to Truckee last Monday with the exact same vehicle and setup I used last summer when reception was zilch and this time it was 99% DFQ. Even copied Green from Auburn at times, and I was never farther west than Exit 180/Donner Lake.
Beats the Hail outta me...