Changes to Clovis and Fresno

[GrumpyGuard]

I noticed that new frequencies have been added to the City of Clovis. I am somewhat confused, as some frequency assignments are duplicates. Channel one and channel two are the same with the same pl. Also channel three and channel four are the same with the same dpl.

How can they be two different channels if all of the information is the same?

 

[Kirk]

I didn't make the changes, but I'm assuming a database administrator received information that those channels are being used in both repeater and direct (simplex) modes. You would program a scanner the same way you always have, with just one of them, but you may notice them reference two different channel numbers on the air. Putting it in both ways adds clarity so when an officer says "Go to channel 4" on the air, you know what's going on. Many departments program radios this way as it's less confusing for them than having a talkaround/direct button on the radio.

 

[GrumpyGuard]

If the same frequencies are being used in both repeater and simplex as two different channels then the pl tones would have to be different. Otherwise the if the dispatcher were using the radio and two officers were to go to channel two they would be talking over each other (doubling), this would cause issues. I have been monitoring this system for the past fifteen years and they have never had anyone request channels two, four or six. I will put the frequency for channel six in my scanner and monitor it.

 

[kma371]

If the same frequencies are being used in both repeater and simplex as two different channels then the pl tones would have to be different. Otherwise the if the dispatcher were using the radio and two officers were to go to channel two they would be talking over each other (doubling), this would cause issues. I have been monitoring this system for the past fifteen years and they have never had anyone request channels two, four or six. I will put the frequency for channel six in my scanner and monitor it.

This was a submission from someone who monitors the frequencies. The PL's don't have to be different. If units are close enough, they would overpower the repeater anyway. The dispatchers wouldn't hear the units on the output anyway, but the units do.

Just so you know, it's common with a lot of agencies for guys to just switch to the output channel and use it as a talk around. They don't have to actually "request" it. It is also a common way of programming for many agencies. And if you haven't heard them, it's possible you weren't close enough to hear them.

 

[Mike_G_D]

If the same frequencies are being used in both repeater and simplex as two different channels then the pl tones would have to be different. Otherwise the if the dispatcher were using the radio and two officers were to go to channel two they would be talking over each other (doubling), this would cause issues.

Completely incorrect! As kma371 stated - this is a VERY common practice and has been since the early days of repeater usage with CTCSS (aka "PL") tones. It's an easy and cheap way for the users of a particular system to have a "car-to-car" channel along with the main dispatch channel without actually having to license a wholly separate frequency. As kma371 said, the dispatchers usually do not monitor the output frequency so will not typically hear the mobiles even if they are close to the receiver antenna used by the dispatcher. Talking on the "car-to-car" channel which uses the repeater output frequency is not frequent enough to cause significant interference to a substantial number of mobiles especially given the relatively low effective radiated power of the mobile transmitters. Using the same CTCSS ("PL") as the main repeater is convenient so as to allow nearby mobiles to hear when another mobile is calling them without even having to be on the actual "car-to-car" channel and also allow the mobiles to still listen for urgent traffic from the dispatcher when on the "car-to-car" channel. This practice, however, is effective pretty much only for analog FM traffic as it depends on the "FM Capture Effect" to work effectively. It does not work so well with the newer digital P25 modes as the LA Police discovered requiring a change in procedures for mobile-to-mobile traffic initiation (dedicated mobile-to-mobile frequency channels and procedures to initiate such traffic) and, of course, it is not used in normal analog or digital trunking operation (at least using the primary trunking system).

-Mike

 

[fresnostatevb13]

Channel 2 and 4 are just the simplex of 1 and 3 which are repeated. Channel 2 is never used and is in place solely for a radio system failure for unit-to-unit comm's if this were to happen. Channel 4 is used as a unit-to-unit channel when in close radius to the other units.