the system here uses Vhf repeaters there are 5 of them on the same channel and offsets all with diffrent pl tones.The problems has started in the last few months that sometimes when the dispatcher is transmitting the dispatcher is cutting in and out and is very distorted.This only happens every so often it is not on every transmission but I would say it happens everyday.
Now another agencie is also having problems they have two repeaters on the same frequencie and diffrent pl tones 75% of their transmissions are un readable.They can not use portables at all
Has anyone ever had this problem.This system has been in place for sometime and is primary Fire/Ems/Police communications.
Repeater Problems
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firefighter13669
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Repeater Problems
KC2VHB
Re: Repeater Problems
Curious as to what agencies this is setup on? I think this is a poor way to setup any system for Emergency services. Five different repeaters all on the same frequincies with only differnt PL tones!!! All in the same general area. This wil cause huge interference issue and these should have been evident from the beginning of the system. Now you can do one repeater with a community tone panel, but this is not a good idea for Public Safety either.
Was this done for coverage issues?
Are there actually different repeater or is it a community tone panel?
I find it strange that they would have all been licensed in the same area on the same frequencies.........
Was this done for coverage issues?
Are there actually different repeater or is it a community tone panel?
I find it strange that they would have all been licensed in the same area on the same frequencies.........
Scott B.
"Never argue with seven men when you are carrying a six shooter..."
"Never argue with seven men when you are carrying a six shooter..."
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firefighter13669
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Re: Repeater Problems
What it is is the county emergency services they do all the fire and ems dispatching.The repeaters are spread out through out the county there are some miles away 10 20 40 miles away.They are all diffrent repeaters at diffrent locations one the rx and tx frequencie the only diff is the pl tones 136.5 179.9 167.9 192.8 127.3
KC2VHB
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psapengineer
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Re: Repeater Problems
Here's a recommendation:
I'd take a look/listen to the "input" frequency and maybe put a Rx on it and listen to it closely. This sounds like co-channel interference on the input frequency with PL different from the PL the dispatcher has selected.
This is a common problem in wide area coverage systems that use multiple repeaters with different PLs. Units in different coverage areas don't hear the distant repeaters and attempt to key up.
Just a guess.............
Bob
I'd take a look/listen to the "input" frequency and maybe put a Rx on it and listen to it closely. This sounds like co-channel interference on the input frequency with PL different from the PL the dispatcher has selected.
This is a common problem in wide area coverage systems that use multiple repeaters with different PLs. Units in different coverage areas don't hear the distant repeaters and attempt to key up.
Just a guess.............
Bob
Re: Repeater Problems
Just forget trying to make this "rig" work. Put the departments on separate channels, like should have been done in the beginning and eliminate a never-ending headache.
I've seen a few plants and companies try to work the "different code-one repeater" set-up and it always boiled down to trying to go on the cheap or a salesperson's ignorance. I usually heard, "well I was told I had my own private channel..."
I've seen a few plants and companies try to work the "different code-one repeater" set-up and it always boiled down to trying to go on the cheap or a salesperson's ignorance. I usually heard, "well I was told I had my own private channel..."
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psapengineer
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Re: Repeater Problems
Ummm,
I guess we should have asked if the repeaters all use the same Tx PL code for "outbound" traffic. Normally in public safety dispatch systems all of the repeaters (on a given channel) for a given dispatch area use a common-single Tx PL. Then each repeater's Rx has it's unique PL so the mobiles and portables can select the closest repeater.
How's your system configured? Is it just differnt inbound PLs or are the outbound PLs different too, or is it carrier squelch Rx for the mobiles.
I do have to say that putting all agencies (areas) on different channels is a nightmare for the dispatch center, frequency coodination, console configuration, and the dispatcher having to listen to 5 channels instead of 1.
I guess we should have asked if the repeaters all use the same Tx PL code for "outbound" traffic. Normally in public safety dispatch systems all of the repeaters (on a given channel) for a given dispatch area use a common-single Tx PL. Then each repeater's Rx has it's unique PL so the mobiles and portables can select the closest repeater.
How's your system configured? Is it just differnt inbound PLs or are the outbound PLs different too, or is it carrier squelch Rx for the mobiles.
I do have to say that putting all agencies (areas) on different channels is a nightmare for the dispatch center, frequency coodination, console configuration, and the dispatcher having to listen to 5 channels instead of 1.
Re: Repeater Problems
Our county fire channel is done the same way. Even better, our firegrounds are simplex on the repeater out with different PLs. It really sucks...
Re: Repeater Problems
Using the repeater output as a fire ground channel is a common practice. The big question
come now on how the PL tones are set up. Once had a radio shop convince the fire chief
of a department that by going to a different PL tone, the department created a new channel.
This didn't work at all since once the users went to the simplex channel use on the repeater
output, they couldn't hear the dispatcher. If a call came in while the users were on the
simplex use, they didn't hear the call.
The common way of doing this is to use the same PL as the repeater while on the simplex
use of the channel. This way everyone hears what is coming out of the repeater as well
as the local fire ground simplex use. If another call comes in and is dispatched, everyone
still hears the new call being sent out over the repeater.
Jim
come now on how the PL tones are set up. Once had a radio shop convince the fire chief
of a department that by going to a different PL tone, the department created a new channel.
This didn't work at all since once the users went to the simplex channel use on the repeater
output, they couldn't hear the dispatcher. If a call came in while the users were on the
simplex use, they didn't hear the call.
The common way of doing this is to use the same PL as the repeater while on the simplex
use of the channel. This way everyone hears what is coming out of the repeater as well
as the local fire ground simplex use. If another call comes in and is dispatched, everyone
still hears the new call being sent out over the repeater.
Jim
tvsjr wrote:Our county fire channel is done the same way. Even better, our firegrounds are simplex on the repeater out with different PLs. It really sucks...
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psapengineer
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Re: Repeater Problems
Jim (etal),
We did a similar thing here in our county. We have separate fire tatical frequencies for the two populated areas of our county. But, for the repeater output, we program one of the modes in the mobile radio to Tx/Rx simplex on the repeater output with the repeater output Tx PL and Carrier Squelch Rx. In this mode they can hear everything on the channel, it works for simplex interoperability during mobilizations when our units encouter other units that use the same frequency, and finally, our units can use it to hail each other if our repeater (voted five site simulcast) goes down or they wander out of coverage.
We did a similar thing here in our county. We have separate fire tatical frequencies for the two populated areas of our county. But, for the repeater output, we program one of the modes in the mobile radio to Tx/Rx simplex on the repeater output with the repeater output Tx PL and Carrier Squelch Rx. In this mode they can hear everything on the channel, it works for simplex interoperability during mobilizations when our units encouter other units that use the same frequency, and finally, our units can use it to hail each other if our repeater (voted five site simulcast) goes down or they wander out of coverage.
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chpalmer
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Re: Repeater Problems
Id look at your input freq to see if any one else in the area has started using it. Even the output for that matter...
We have a customer with the same thing here with 5 fire repeaters, all out on 110.9 but different inputs. Were looking to simulcast later but we need the infrastructure to allow that first.
We have a customer with the same thing here with 5 fire repeaters, all out on 110.9 but different inputs. Were looking to simulcast later but we need the infrastructure to allow that first.
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firefighter13669
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Re: Repeater Problems
The way the system is set up is that rx is 154.355 tx 151.355 with all diffrent pl tones.The system has been in use for many years and keep adding diffrent repeaters.The dispatch centers changed all their consoles over and since they did this they have had several problems.The sheriffs dept has the same problems they run two repeaters on the same tx rx channels.But the covrage has gone down hill and alot of transmissions are distorted.They have also had alot of problems with one car on one repeater and another car on another its will distort the first 3 secs of the transmissions ect lots of problems with both systems but they all started with in the last 5 to 6 months
KC2VHB
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kb4mdz
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Re: Repeater Problems
If a lot of this started when the consoles got changed, maybe that's a clue to other problems. What consoles were they using, what did they go to, or how else did things change?
Prime example of why a proper program of preventative maintenance, and using a good two-way radio shop, are important to operation of a Public Safety system. Right now, it could be one or a dozen problem aspects to the system.
psapengineer has a good idea, if you're close enough, and dispatch talks thru control stations; listen on the input frequency, and esp. for any differences in audio between different repeaters; that brings up another point; do the repeater outputs all sound pretty much the same, or are they wildly different? If they're different, I'm willing to bet dollars to (Dunkin' ) donuts that audio levels are all squee-hawed, too.
Prime example of why a proper program of preventative maintenance, and using a good two-way radio shop, are important to operation of a Public Safety system. Right now, it could be one or a dozen problem aspects to the system.
psapengineer has a good idea, if you're close enough, and dispatch talks thru control stations; listen on the input frequency, and esp. for any differences in audio between different repeaters; that brings up another point; do the repeater outputs all sound pretty much the same, or are they wildly different? If they're different, I'm willing to bet dollars to (Dunkin' ) donuts that audio levels are all squee-hawed, too.
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chpalmer
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Re: Repeater Problems
Are they using VOIP links?
What equipment is involved?
What equipment is involved?
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psapengineer
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Re: Repeater Problems
OK, let's talk about the distorted 3 seconds...........
Repeaters have a set up time. Its the time for the repeater receiver to hear the signal, detect the PL, key the transmitter, and for the listening mobiles to hear the signal, detect PL and unmute the speaker. In a typical repeater system the "hang time" is set to about 3 or 4 seconds. This allows the person who answers within the hang time to not have their first couple of syllables cut off by the set up time if they answer quickly.
If the rigs are using the same repeater this works well; if they are on different repeaters it works poorly. The next person answering on a different repeater does so before the hang time of the first repeater expires. The listening rigs hear both repeaters during the hang time. Their discriminators recover the Rx PL from both receivers and the sum/difference of the carrier frequencies of the transmitters. The squeal or howl that is heard is called a heterodyne.
Shortening the hang time to 0 makes this better but aggravates the loss of the first syllable problem.
Most dispatch centers call themselves something like "firecomm" or somthingcomm. The rigs hail the dispatch center by calling something like "firecomm -- Engine 711" and the dispatch center hails by saying something like "Medic 991 -- firecomm". That procedure doesn't work in a multi repeater system since it doesn't identify which repeater is being used for the exchange.
Instead a procedure that replaces the name of the dispatch center with the geographical name of the repeater could be used. If the repeater is on a hill serving the community of "BobTown" the rig hailing the dispatch center would sound like this: "Engine 711 -- BobTown" This lets everyone know which repeater is being used and helps with the challenge. The dispatch center does similar: "BobTown -- Medic 991".
It is important that the all of the repeaters are using the same TxPL and all mobiles and portables are using the same RxPL (or carrier squelch). There is probably no getting around this.
Lastly, I need to make a comment about the future of your system….
The collisions that happen in a multiple repeater system increase exponentially as the calls for service increase linearly. Poisson tables describe the probability of multiple events happening at the same time given their duration and rate of occurrence. Your system is likely at the point where you need to consider some significant design changes.
Read this article and make sure it gets to your decision-makers as well as the dispatch center:
http://mrtmag.com/mag/radio_jps_communications_case/
It explains why and how you can fix this kind of problem and the financial incentive for doing so.
Best Regards,
Bob
Repeaters have a set up time. Its the time for the repeater receiver to hear the signal, detect the PL, key the transmitter, and for the listening mobiles to hear the signal, detect PL and unmute the speaker. In a typical repeater system the "hang time" is set to about 3 or 4 seconds. This allows the person who answers within the hang time to not have their first couple of syllables cut off by the set up time if they answer quickly.
If the rigs are using the same repeater this works well; if they are on different repeaters it works poorly. The next person answering on a different repeater does so before the hang time of the first repeater expires. The listening rigs hear both repeaters during the hang time. Their discriminators recover the Rx PL from both receivers and the sum/difference of the carrier frequencies of the transmitters. The squeal or howl that is heard is called a heterodyne.
Shortening the hang time to 0 makes this better but aggravates the loss of the first syllable problem.
Most dispatch centers call themselves something like "firecomm" or somthingcomm. The rigs hail the dispatch center by calling something like "firecomm -- Engine 711" and the dispatch center hails by saying something like "Medic 991 -- firecomm". That procedure doesn't work in a multi repeater system since it doesn't identify which repeater is being used for the exchange.
Instead a procedure that replaces the name of the dispatch center with the geographical name of the repeater could be used. If the repeater is on a hill serving the community of "BobTown" the rig hailing the dispatch center would sound like this: "Engine 711 -- BobTown" This lets everyone know which repeater is being used and helps with the challenge. The dispatch center does similar: "BobTown -- Medic 991".
It is important that the all of the repeaters are using the same TxPL and all mobiles and portables are using the same RxPL (or carrier squelch). There is probably no getting around this.
Lastly, I need to make a comment about the future of your system….
The collisions that happen in a multiple repeater system increase exponentially as the calls for service increase linearly. Poisson tables describe the probability of multiple events happening at the same time given their duration and rate of occurrence. Your system is likely at the point where you need to consider some significant design changes.
Read this article and make sure it gets to your decision-makers as well as the dispatch center:
http://mrtmag.com/mag/radio_jps_communications_case/
It explains why and how you can fix this kind of problem and the financial incentive for doing so.
Best Regards,
Bob
Last edited by psapengineer on Sat Sep 15, 2007 9:32 am, edited 2 times in total.
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psapengineer
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Re: Repeater Problems
On to a bit about consoles:
Can you tell us what the console configuration is? Is there one control station per repeater or just one control station for the system?
Let's say there are 8 repeaters in this example.
If the channel is configured as T8-R8 it is likely configured correctly for you application if the repeaters have a common TxPL or T8-8R if the repeaters are using different TxPLs.
If its configured as 8ea T1-R1 without cross-busy/cross-mute it's probably not OK if there are multiple control stations.
In short, the console has to be configured such that the dispatcher can only select one of the repeaters at a time. Simul-Select (not to be confused with simulcast - which is an RF technology) can't be used to select multiple repeaters at the same time on the same channel....
Lastly, consoles and control stations, be set to key on each scroll through the PL list. So, if the dispatcher is having to "scroll" down through a list of PLs and choose the new one, it may be keying the last repeater(s) and then the new repeater putting both (or more) on the air for the first few seconds of the first transmission.
Regards, Bob
Can you tell us what the console configuration is? Is there one control station per repeater or just one control station for the system?
Let's say there are 8 repeaters in this example.
If the channel is configured as T8-R8 it is likely configured correctly for you application if the repeaters have a common TxPL or T8-8R if the repeaters are using different TxPLs.
If its configured as 8ea T1-R1 without cross-busy/cross-mute it's probably not OK if there are multiple control stations.
In short, the console has to be configured such that the dispatcher can only select one of the repeaters at a time. Simul-Select (not to be confused with simulcast - which is an RF technology) can't be used to select multiple repeaters at the same time on the same channel....
Lastly, consoles and control stations, be set to key on each scroll through the PL list. So, if the dispatcher is having to "scroll" down through a list of PLs and choose the new one, it may be keying the last repeater(s) and then the new repeater putting both (or more) on the air for the first few seconds of the first transmission.
Regards, Bob