PL code

[turtle9832]

I have a question regarding pl codes and their use on a single frequency.

My agency has a UHF system where HT1000's are used along with various mobiles.

We have one channel that goes through a repeater system on pl code 146.2.

We have a back up channel that is on the same frequency but does not go through the repeater and also is on pl code 146.2.

We programmed some of our HT1000's on a different channel with our the same frequency with a different pl code of 77.0.

We were able to talk on the channel with the pl code of 77.0 and not be heard on the main channel.

My question is, why does the traffic on the channel with a pl code of 77.0 sound, "stepped on" when there is traffic on the channel programmed with the pl code of 146.2 at the same time?

[Jim202]

I have a question regarding pl codes and their use on a single frequency.

My agency has a UHF system where HT1000's are used along with various mobiles.

We have one channel that goes through a repeater system on pl code 146.2.

We have a back up channel that is on the same frequency but does not go through the repeater and also is on pl code 146.2.

We programmed some of our HT1000's on a different channel with our the same frequency with a different pl code of 77.0.

We were able to talk on the channel with the pl code of 77.0 and not be heard on the main channel.

My question is, why does the traffic on the channel with a pl code of 77.0 sound, "stepped on" when there is traffic on the channel programmed with the pl code of 146.2 at the same time?

It's real simple, remember the law of physics where it says that 2 bodies can't occupy the same space at
the same time. Well in radio it's the same way. You can't have two conversations going on at the same
time on the same frequency in the same close area.

The different PL tones only mute the receiver. It doesn't let you hear what else is going on on the channel
if you don't hit the monitor button. Back in the deep bowls of part 90 of the FCC rules and regulation it
says that your suppose to monitor the frequency before transmitting. Maybe you should go back to the
clown that did the frequency coordination and ask why multiple users are on the same channel with
different tones. Wait, let me guess, the tones were just picked because some radio guy said it would work.

Jim

[turtle9832]

Im the clown

I read and did research here first.

I posted the question before moving forward.

Thanks for the physics lesson.

Our agency like others is short on cash, that's why I came here for answers.

My boss came to me looking for alternatives to what we have now,

Thanks again

[Tom in D.C.]

The stuff we do here ain't rocket science, usually, but you must have more than a sketchy knowledge of how
radio systems operate before you start working on them. Your boss should know better than to treat a service that's
moderated and controlled by the FCC like it's something than can be casually fiddled with. Following orders and
doing your best probably wouldn't get you in trouble but it could mean trouble for the agency. Call in the people
who built the system, even though it costs a few bucks, and get things sorted out properly, and if your boss
complains tell him you got professional advice and you're just trying to save him possible embarrassment.

[Bill_G]

By his description, it's simply a misunderstanding of what PL does.

t9832 - PL allows you to hear traffic specifically for you on a shared channel. It is a secondary qualifier. The first qualifier is on frequency transmitter energy. All rcvrs within range will pick that up. If the correct PL (or DPL) is detected, then the rcvr will unmute. If not, then the rcvr will remain muted, and you will not be disturbed by co-channel users.

All frequencies are shared to some extent, and for a long time PL was the only method available to keep your radio quiet while others used the channel. You didn't have to, or want to, listen to all the traffic. You could easily miss a call for you as your ear sifted through the chaff. The higher the population density, the worse the problem got. PL helped you hear just your traffic. As already pointed out, only one user could transmit at a time. PL does nothing to prevent that. Hence the requirement to monitor before transmitting.

[turtle9832]

Thank you Bill.

I appreciate you seeing my question and my misunderstanding.

We have had our uhf system for about 20 years. When I learned about mdc, i wondered why our agency didnt have it. This board helped me learn about mdc and put into place (by a professional mss). My boss now comes to me with radio questions becuase I have taken an interest in radios now.

I have now gone to him and explained how pl codes work.

Thanks.

Respectfully,

Turtle

[Bill_G]

You're welcome turtle. It sounds like what your agency needs is another frequency - a local car to car, or tac channel - that doesn't go through the repeater so you can conduct your business without disturbing, or being disturbed by, the main traffic. Depending on your location, that may or may not be easy to do. The closer you are to a major metro area, the harder it is to find an open channel. But, it is not impossible. Talk to your radio shop.