Blount County Fire interference

[W4TRX]

On the Blount County Fire dispatch frequency 158.8350 (input 154.070), I frequently hear another fire dispatch. The audio sounds noisy, distorted and "off frequency". According to RR, there is a 186.2 Hz PL tone on the Blount repeater, but enabling this on my analog receiver does no good - the other station still comes in strong. That leads me to believe the interfering transmission is on the Blount County input frequency, and therefore is getting retransmitted, but if so, that means the input PL tone is not being used on the Blount repeater or is the same frequency as the interferring station - not likely.
There are other repeaters in Alabama with an output freq near the input frequency of the Blount repeater, but all have a different PL tone.
I don't know if the dispatchers are hearing the interference - I never hear any comments about it. I know others are hearing it; I have a friend who monitors and complains about it also. The most aggrivating part is the distorted interference is as loud, or louder than the normal dispatch traffic.
I was especially disappointed to hear the same interference on their digital channel (AIRS TG43012)

The only other situation I can imagine is that skip is being received by the Blount County repeater, and has the same input PL tone. But that doesn't explain how the interference is transmitted on the digital channel.

I've heard this for the last couple of years.

Any ideas?

 

[TomServo]

It definitely sounds like skip is getting into the input frequency of the analog repeater from somewhere. I don't know how their system is setup but if there's a mix of digital and analog users then the analog repeater is still going to be in use and tied to the AIRS talkgroup.

This happens to the Fairhope ops channel on AIRS; it's tied to their analog repeater since Fairhope is all volunteer and not everyone has a P25 radio. IIRC, it's the Marion County sheriff dispatch that gets into the fire repeater, and it goes out over the analog and AIRS talkgroup at the same time. Very annoying but like your situation, no one on the radio ever seems to complain about it.

 

[W4TRX]

it's tied to their analog repeater since Fairhope is all volunteer and not everyone has a P25 radio. IIRC, it's the Marion County sheriff dispatch that gets into the fire repeater, and it goes out over the analog and AIRS talkgroup at the same time.

Same situation here - many small analog only departments so they have to simulcast them on AIRS. And, sounds like skip is the problem. I just wonder if they don't have their CTCSS enabled on the input. Seems like that would take care of that problem. Thanx.

 

[cavmedic]

Same situation here - many small analog only departments so they have to simulcast them on AIRS. And, sounds like skip is the problem. I just wonder if they don't have their CTCSS enabled on the input. Seems like that would take care of that problem. Thanx.

PL in the input might prevent the transmissions from keying the other repeaters, but will NOT eliminate the interference. It is entirely Possible for the PL's to be the same.

 

[W4TRX]

PL in the input might prevent the transmissions from keying the other repeaters, but will NOT eliminate the interference. It is entirely Possible for the PL's to be the same.

It won't eliminate the interference, but that would keep me from hearing it!

That must be what's happening - skip with the output frequency of the interfering source near the input freq of the Blount County repeater, and either they (Blount) don't have their receive PL enabled, or the interfering source has theirs set the same (186.2 Hz).

It's so annoying at times (especially at night) that I just turn the radio off.

 

[Avery93]

This happens to the Fairhope ops channel on AIRS; it's tied to their analog repeater since Fairhope is all volunteer and not everyone has a P25 radio. IIRC, it's the Marion County sheriff dispatch that gets into the fire repeater, and it goes out over the analog and AIRS talkgroup at the same time. Very annoying but like your situation, no one on the radio ever seems to complain about it.

Interesting you mention this. Years ago I heard a Marion County officer on a mobile radio in Hamilton transmitting directly into the Fairhope repeater, and I was able to monitor this on the Fairhope repeater from Marion County full scale on a scanner. VHF ducting does some crazy stuff. Every now and then Baldwin Central gets into the Marion County repeater, but it's rare.

That must be what's happening - skip with the output frequency of the interfering source near the input freq of the Blount County repeater, and either they (Blount) don't have their receive PL enabled, or the interfering source has theirs set the same (186.2 Hz).

Almost 100% chance it is a signal with the same input PL. When you only have 38 combinations (with PL), there will almost always be some distant signal with the same PL duct into a repeater at some point in time. DPL helps with 83 combinations, but it can still happen. If the repeater was in carrier squelch receive, it would likely be constantly blasting all kinds of traffic and noise from multiple stations due to frequency re-use and ducting.

Trying to correct recurring interference like this can be a massive undertaking on a countywide level. Every radio and base station would have to be re-programmed in a coordinated fashion.

 

[morganAL]

Years ago, radio shops that serviced systems for multiple counties would often use the same CTCSS (PL) tone in all of the systems. That kept the shops from having to stock multiple tone modules. They would buy a quantity of whatever was in use locally and have spares for radios no matter which system the radio belonged to. Locally, everything used to be 123.0. Most of the radios in a 3 or 4 county area were GE MASTR II. Over the years, as systems have upgraded and radios got better, the need to reduce co-channel interference or just cut down on fatigue from listening to something that wasn't relevant, CTCSS tones were changed and some even went to DPL/DCS.

Way back in the ancient days when I was a dispatcher, we routinely heard Nashville Metro South. Some nights, the officers in the cars heard them too. The repeaters didn't transmit CTCSS. Everything was carrier squelch. Late one evening, Nashville had something going on and things got wild. Skip was fading in and out and all of the cars and dispatch heard "**garbled*** shots fired! shots fired! One down *garbled* **static** need EMS!!" and that was all we heard. Needless to say things got hectic for a minute. Dispatch was pretty sure it was Nashville Metro because we were familiar with the way they sounded. The patrol supervisor made us do a roll call. I had another dispatcher call Nashville to verify. Shortly after, there was a reprogramming of radios and repeaters. We could see the busy light indicating activity on the channel, but at least we didn't have to hear them.

 

[radiogod_2103]

I hear it to on the palmerdale site of the jefferson county sites.
From what i have seen on the blount co fire fighters association website under board mins. They are trying to get a law suit agst. motorola. also some talk of changing a tone. I think the blount county part was just a rush job and not planned out. They have said many times they need more towers. They are only 2 sites for all of blount co. Also first net with vhf back up has been thrown on the table .

911 Board:
● Televate gave (3) different scenarios to choose
1.) $4.8 million on services. 4 more towers
2.) $2.9 million N70 through motoroyla with VHF backup
3.) $1.3 million First Net with VHF backup possible
-$178,000 per year
-New repeaters, radios, and antennas

911 Board:
● Motorola Mediation - Motorola did not budge. Will be on the docket for
Federal Court at some point.
● Once tone is found, will be scheduling reprogramming
● Equipment is 30+ years old, will be revamped.

 

[morganAL]

I hear it to on the palmerdale site of the jefferson county sites.
From what i have seen on the blount co fire fighters association website under board mins. They are trying to get a law suit agst. motorola. also some talk of changing a tone. I think the blount county part was just a rush job and not planned out. They have said many times they need more towers. They are only 2 sites for all of blount co. Also first net with vhf back up has been thrown on the table .

911 Board:
● Televate gave (3) different scenarios to choose
1.) $4.8 million on services. 4 more towers
2.) $2.9 million N70 through motoroyla with VHF backup
3.) $1.3 million First Net with VHF backup possible
-$178,000 per year
-New repeaters, radios, and antennas

911 Board:
● Motorola Mediation - Motorola did not budge. Will be on the docket for
Federal Court at some point.
● Once tone is found, will be scheduling reprogramming
● Equipment is 30+ years old, will be revamped.

If the equipment is 30+ years old, they are operating illegally anyway. Everything was mandated to go narrowband by the FCC by 2013 and I doubt anything 30+ years old in narrowband capable. I knew of some shops that turned down the deviation so the customer was "compliant" with the narrowband mandate but I'm pretty sure that is NOT what the FCC had in mind. Yeah, you are meeting the deviation standard but the equipment isn't FCC type accepted for narrowband.