Multiple PL tones on a single frequency

[W3AWF]

I have a question about utilizing multiple PL tones on a single frequency. The borough that I am employed for as an Emergency Management Coordinator and Fire Marshal has tasked me with solving some communications issues. Being that the borough is 1.2 square miles, and is relatively flat, we have a single VHF frequency licensed to us that we utilize as a simplex frequency due to the small size of the municipality. This frequency is currently only utilized by the public works department however we are currently in the process of adding more users to provide more efficient interoperability. The current idea is to utilize the single frequency that we have licensed to us with multiple PL tones to separate the fire department, police department, public works, and the office of emergency management. The issue that I am concerned about is that in the event that all agencies are utilizing there respective channels, would we experience any issues such as receiver overloading? This may be a simple question however without having a background in electrical engineering I am unable to intelligently answer the question with 100% certainty.

Thank you in advance for any assistance provided!

 

[buddrousa]

Most scanners I own I can have the same frequency with several tones
Ch 1 Police 1 460.350 127.3
Ch 2 Police 2 460.350 203.5
Ch 3 Police 3 460.350 100.0

 

[wtp]

the problem will come

when groups try to call each other at the same site.
with a pl tone you can't hear the other guy and will try to get your guy.
the two options are separate frequencies for each or about 2 miles apart (just a guess).
it would sound like CB channel 6 to someone with a scanner and no tone, everybody all at once.

 

[KB7MIB]

In order for this to work, every radio would need to have a busy channel lockout programmed in to prevent one department from transmitting at the same time that another department is already transmitting.
This presents a safety issue for the police officers and firefighters who may need to communicate NOW, and not when the dog catcher or trash truck driver or water meter reader is done talking.

I would strongly suggest, if for no other reason than officer and firefighter safety, that at least those two departments are not included in this scheme. Those two departments should have their own separately assigned, and licensed, channels.

The only reason for every department and every employee assigned a radio to be on the same channel, should be for inter-departmental communications during a major event requiring it. And then everyone needs to have the same CTCSS or DCS (PL or DPL) programmed into their radio.

John
Peoria, AZ

 

[mmckenna]

Yes, it can be done. No, you should't do it.

Not really sure what you mean by "receiver overloading" in this sort of installation, though.

Mixing public safety and public works on a simple frequency with PL/DPL tones as the separator can lead to issues.
Busy lock out on the radios can prevent "collisions", however people will not know why it's doing it if they cannot hear the traffic. You'll get told "The radios never work". Or, "There's something wrong with my radio", and you'll either spend a lot of time trying to explain why it's set up this way, or trying to track down nebulous radio issues that your users will not be able to effectively explain.

At minimum, you should have your public safety on a separate system. Fire and PD don't always work together well, so you might have some issues there, but at least there is some divider.

Since it sounds like you really only need a simplex system, adding an additional channel isn't really that hard. Ideally, separate site so you have some survivability. If funding is the reason for not doing this, then the Borough needs to really rethink their priorities. They probably shouldn't be in the public safety business if they cannot afford or will not provide suitable systems.

 

[KC3ECJ]

I have a question about utilizing multiple PL tones on a single frequency. The borough that I am employed for as an Emergency Management Coordinator and Fire Marshal has tasked me with solving some communications issues. Being that the borough is 1.2 square miles, and is relatively flat, we have a single VHF frequency licensed to us that we utilize as a simplex frequency due to the small size of the municipality. This frequency is currently only utilized by the public works department however we are currently in the process of adding more users to provide more efficient interoperability. The current idea is to utilize the single frequency that we have licensed to us with multiple PL tones to separate the fire department, police department, public works, and the office of emergency management. The issue that I am concerned about is that in the event that all agencies are utilizing there respective channels, would we experience any issues such as receiver overloading? This may be a simple question however without having a background in electrical engineering I am unable to intelligently answer the question with 100% certainty.

Thank you in advance for any assistance provided!

Can't the police,fire,and EMA use interop frequencies any public safety agency can use? Could you clarify more on what you are asking?

 

[buddrousa]

Yes but not for regular dispatch use. Multiple agencies working the same scene is the intent of Interop.

 

[lmrtek]

I have many small towns and repeater systems utilizing up to 8 different PL tones and they get by just fine most of the time.

All radios need to have busy channel lock out enabled, time out timers
set to 60 seconds or less, and everyone will need to be trained to keep their transmissions as short as possible and listen for and yield to emergency communications.

 

[SCPD]

I wouldn't do this for police and fire. WhIle it could serve as a police side channel with different tone you would want fire and police having their own channels. A fireground channel on its own also.

 

[SCPD]

I have many small towns and repeater systems utilizing up to 8 different PL tones and they get by just fine most of the time.

All radios need to have busy channel lock out enabled, time out timers
set to 60 seconds or less, and everyone will need to be trained to keep their transmissions as short as possible and listen for and yield to emergency communications.

While it works it opens up a can of worms when a officer needs backup or fireman goes down trying to key out getting a nice bonk. It'll never happen here its too small here cannot be used as a excuse.

 

[NC1]

Assuming there are no repeaters, all that is needed is a couple more frequencies allocated to your town.

Where I grew up, about 3 square miles for the Borough, all they needed was 4 simplex frequencies. Police, Fire, Ambulance, and Public Works. No repeaters.

Since there was a lot of overlap where people from one department also belonged to another, only one radio was needed for each person and/or vehicle. This served the town very well because the guy sweeping the streets was also on the Fire Dept, so all he needed to do was switch to the FD Channel. Some on the FD were also EMT's who could just change channels if the ambulance was short handed.

Now this also had a big advantage as far as having spare equipment available and ready should it be needed at a moments notice. All the chargers and accessories would fit on any radio because they were all the same across the board. Nothing went to waste because everything could be used.

It's a win/win all the way around.

 

[Danny37]

Police and fire should have their own separate respective frequency. Emergency communications need to be stable and I think even tho you say repeaters aren't necessary they still should be implemented in case of dead spots and out of bound incidents that may take place or lead to another location such as a police pursuit etc.

Public works on the hand can work simplex with different pl tones but a busy channel lockout would be a good idea.

 

[PrivatelyJeff]

I would also say talk to neighboring communities and see if you couldn’t work together on something. If your fire and EMS have a mutual aid agreements, maybe maybe you can share radio services as well.

 

[mdsxfire]

I would also caution against the “small town” argument. My town is just over 4sq miles and while the FD only averages about 3 calls a day a lot of those calls the Pd is operating with us to close roads or other valuable ops on top of regular patrol MV stops alarms etc and with any major calls ems is also on scene. Yes in between those fire calls it would be the pds channel solely but I have enough problems tryin to get an urgent transmission out with responding units talking at a fire


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