Access and/or listen to a particular repeater - if both have same Freq & PL??

This forum is for discussions regarding System Infrastructure and Related Equipment. This includes but is not limited to repeaters, base stations, consoles, voters, Voice over IP, system design and implementation, and other related topics.

Moderator: Queue Moderator

Post Reply
New User
Posts: 3
Joined: Thu Jul 07, 2011 1:21 pm

Access and/or listen to a particular repeater - if both have same Freq & PL??

Post by Sagacious »

I couldn't think of a more concise way to elucidate my question, so I'll attempt to explain if it isn't clear. :/

I have a base station setup comprised of a Quantar an an AstroTac receiver operating in Conventional Analog. The Quantar is channel steered by the Function Tone table via VOIP from a remote Dispatch location. The Rx Audio from the AstroTac is sent to Dispatcher via VOIP as well.

So, the purpose of the base station(s)... to listen to and key up several repeaters that are within it's range. The repeaters are all the same freq & just different PL. The AstroTac is programmed with 1 channel (the repeater output freq) and MultiPL, so it receives all the different repeater traffic within its range. The Quantar is programmed to transmit the repeater input, on a per channel basis for each PL. So, however many repeaters the AstroTac is listening to is how many repeater input channels the Quantar is programmed to transmit. For the sake of being thorough, there is one more (simplex) channel programmed in the Quantar for local traffic. Continue this scenario throughout the state and a handful base stations are listening and responding to (potentially) a dozen repeaters at a time. The repeaters are all geographically spaced far enough apart where a subscriber would not be able to key up two with the same PL at once and none will heterodyne.

However, there's an unintended consequence due to this arrangement/configuration... I'm sure some of you probably already foresee what that is. ;p

Here's the issue, there are instances where a base station (due to its overall elevation) can key up 2 repeaters of the same PL at once. So, one of those repeaters we didn't intend to key up is part of a different group of repeaters that is normally heard and keyed up by a different base station. So, for example if I'm at a dispatch location and try to key up the "Tall Mountain - 6Z" repeater via the "City X" base station; I've also unintentionally keyed up the "Mid Mountain - 6Z" repeater which is heard by it's 'parent' base station in "City Y". Which means, every time the dispatchers key up "Tall Mountain - 6Z", they will get an RX indication on the console for BOTH "Tall Mountain 6Z" and "Mid Mountain 6Z" under their respective Base Station columns. There are instances where I've seen one of our base stations (580ft transmit) key up a total of 3 repeaters of the same PL (1 intended, 2 unintended) that would display 3 RX indication lights on the console. Scale this problem up and this would get unnecessarily confusing for dispatchers.

So, my question is: How can I fix this?? First thing I should say is, I'm trying everything I can to come up with a solution OTHER than re-arranging repeater PLs geographically and subsequently having to reprogram all the subscriber units. Here's my only thought... I don't really care about keying up unintended repeaters of the same PL, I think we can live with that IF there is a way I could get these AstroTac (OR GPW-8000) receivers to uniquely identify, and only open squelch for a particular 6Z repeater. (I'm just arbitrarily picking 6Z as an example.) There would have to be something "added" to the transmit of this 6Z repeater, that identifies which 6Z it is, which would then be programmed in it's intended Base Station (AstroTac) so the receiver would only open for that particular 6Z with its unique identifier and no other 6Z. Something like this would fix the problem of multiple base station RX indication lights displaying on the console and eliminate dispatcher confusion. (Again, this change would have to be transparent to subscriber operation.) So, I've come up with a hypothetical solution--can anyone think of a practical way to implement something like this? Is there an easy way to do this that I'm over looking? or a different approach anyone can think of? sorry for the long post and lengthy explanation, I figure it's usually best to give the whole picture so people have the latitude of clever "out of the box" solutions. I appreciate any help, thanks.
User avatar
Posts: 3504
Joined: Tue Mar 19, 2002 4:00 pm

Re: Access and/or listen to a particular repeater - if both have same Freq & PL??

Post by d119 »

You need to change PL on one of the repeaters. Having the same frequency and PL within the same geographic area, regardless of overlap or lack thereof, is bad business.

You could change the power output level of the Quantar, but that's a band-aid and not a solution.
Posts: 61
Joined: Thu Nov 06, 2014 9:53 am

Re: Access and/or listen to a particular repeater - if both have same Freq & PL??

Post by Wiregeek »

first thing I can think of is MDC or other signalling at the repeater, but that's pretty ugly. Alternatively, switch to wireline - also ugly. Upgrading to Astro digital systemwide would allow more available NAC to prevent mis or multi key, but is hideously ugly.

I don't think there's a "good" solution here at all - but I don't see a solution that avoids reprogramming the fleet, either.
Posts: 3582
Joined: Sun Sep 09, 2001 4:00 pm

Re: Access and/or listen to a particular repeater - if both have same Freq & PL??

Post by Jim202 »

The solution is not a simple solution. Just changing the input required PL sounds like a solution, but it comes with a big "BUT".

You have to consider how many other radios there are that are currently using the PL on that station. It means going to each of those radios and programming in the new PL that was chosen. This is a very large, labor intensive solution. Not only does it take the time of the radio tech, but it also means the user who has the radios is down for the duration it takes to meet up with the radio tech, get the radio or radios programed and then get back to their normal activity. It could mean several hours in just travel time just to meet up with the radio tech depending on the location of the meeting.

Changing a PL in a large operational radio system is not something that should be taken for granted. It has major repercussions that come with it.

User avatar
Posts: 3087
Joined: Thu Sep 17, 2009 5:00 am

Re: Access and/or listen to a particular repeater - if both have same Freq & PL??

Post by Bill_G »

Using common repeater freq pairs with common tx PL, and unique rx PL is called multi-cast, aka poor man's simulcast. It's a popular strategy to increase a channel footprint without any intertie backbone. The biggest weakness of this strategy is it requires the users to figure out which is the best site to use for their location.
Posts: 124
Joined: Fri Sep 07, 2001 4:00 pm

Re: Access and/or listen to a particular repeater - if both have same Freq & PL??

Post by maxjam »

if you are only running analog, the quantars can decode 2 pls. You could keep all repeater listening to a common RX pl that the subscriber units would use and then a different unique PL that the base station would transmit that would only bring up the desired repeater.
Posts: 1062
Joined: Fri Nov 02, 2001 4:00 pm
What radios do you own?: Over 50 - All Motorola

Re: Access and/or listen to a particular repeater - if both have same Freq & PL??

Post by com501 »

If this is a statewide system, then most or all radios will have multi-PL select. IF not, pick the repeater with the fewest 'users' and do as d119 suggested. One of those repeaters will ahve to get a new PL code. This problem is a result of poor planning and resource configuration.
Post Reply

Return to “Base Stations, Repeaters, General Infrastructure”