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Repeater Transmitting DTMF Tone Daily

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kenwoodgeek

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Feb 1, 2015
Messages
218
Location
Wheaton, IL
Hi, everyone,

Wasn't sure where to post this, so I put it here. I do not own this repeater; I'm just the radio geek at my work that works on the radios, to some extent. Just looking for an answer out of curiosity, and to possibly give helpful info to our radio maintenance guy.

My bus company uses a conventional UHF repeater for our bus radios and portables. It is and has been a great system for a long time. Just in the past few weeks, though, there has been an ongoing issue that is making myself and all our drivers go crazy.

The repeater (at least I assume it's the repeater) has been transmitting a continuous DTMF tone for roughly 30 seconds every afternoon around the same time this week. It used to do this exact same thing last year and the year before, but it would last about a minute, and it only happened twice or three times a school year. During the first couple weeks of school, it was doing it maybe once or twice a week, but it has progressively gotten worse, to where it is happening every day now.

Here is what I do know. It happens completely randomly. Doesn't matter if someone is in the middle of transmitting, or if the radio has been dead silent for 5 minutes. It lasts about 30 seconds, and then stops. If dispatch keys the base radio over it, that has enough power to block it out, but if anyone farther from the tower tries to transmit, their transmission will just scramble up with the tone. There is no way it could be one of our bus radios, because our radios are not programmed to transmit DTMF tones of any kind, only FleetSync PTT ID. The tone has no FleetSync ID before or after it. I don't see why it would be an outside person jamming our frequency with malicious intent.

My absolute best guess is that something is going out on the repeater, and that it's some kind of an automatic error tone that the repeater is programmed to send out.

Does anyone have a better idea?

Thanks.
 

slicerwizard

Member
Joined
Sep 19, 2002
Messages
7,643
Location
Toronto, Ontario
I don't see why it would be an outside person jamming our frequency with malicious intent.
But that's exactly what it sounds like. This world is full of losers who have nothing better to do. Don't acknowledge the interference in any way on your radios - that just encourages the interloper. Ignore him and he'll get bored and move on.

If you think it's the repeater acting up, why haven't you monitored the input frequency to verify that there's no inbound signal carrying DTMF?
 

R8000

Low Battery
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Joined
Dec 19, 2002
Messages
1,009
We had this problem on a public safety system I maintained. Turns out, it was a Kenwood mobile radio that was turned on and off with a battery master switch in an ambulance.

I work with Motorola stuff only, but the Kenwood radio had some features turned on that apparently had a bug or glitch that would cause a continuous DTMF tone until the radio timed out. I don't know what the fix was (different vendor), but the timing of this happening was after a EMS agency was paged for a call, and the crew would get to the station and flip the master switch on...then the tone came out until the radio timed out. When the ambulance was all done at the hospital and getting ready to return to the garage, they would flip the master switch on and...bam...DTMF tone. I could watch it drive around by watching the JPS voter and seeing the different rx sites light up.

If you are programming your own radios, I might suggest disabling all signalling and features you don't need. If it's new enough maybe a firmware update could help.

If you are running Kenwoods, this is what may be happening and not a jammer.
 

RadioGuy7268

Member
Joined
Mar 11, 2006
Messages
189
Location
PA
Given the time of year, I'd suggest that it's a very distant user who has happened to match your PL/DPL code, and they've got an automated type of system that's spitting out strings of DTMF tones for some other purpose, it just happens to be keying up on your repeater's input.

Google "tropospheric ducting" and you might see why the effect shows up most during spring/fall weather. Given the mention that a similar thing happened last year, that sounds like the most likely suspect - especially since a strong signal from the base can talk over top (FM capture) - but weaker portables can't. The effect is usually more apparent in VHF and lower bands, but it will happen on UHF to a lesser degree.

You might take time to search up other distant users on the repeater's input frequency. See if you can find a golf course or something similar. They often use DTMF to control sprinkler systems.
 

RFI-EMI-GUY

Member
Joined
Dec 22, 2013
Messages
6,859
Is it just one single tone or a sequence of tones? If it is one tone and goes away after 30 seconds, it is likely a mobile with a timeout timer set for 30 seconds. Do any of the mobiles have a keypad on the mike? Any portables with keypad on the front panel? How about other agencies sharing the repeater? It could simply be something bumping the microphone or water damage in the keypad.

Also you should monitor traffic for any radios absent the fleetsynch. Maybe some radios have been misprogrammed or an old spare pressed into service.
 

a417

U+0000
Joined
Mar 14, 2004
Messages
4,650
and the crew would get to the station and flip the master switch on...then the tone came out until the radio timed out. When the ambulance was all done at the hospital and getting ready to return to the garage, they would flip the master switch on and...bam...DTMF tone. I could watch it drive around by watching the JPS voter and seeing the different rx sites light up.

If it was a moto, i'd say someone didn't jumper the emergency button pin, and the radio is powering up right into an emergency state.
 

Ant9270

The Green Weenie
Joined
Aug 31, 2018
Messages
493
Almost sounds like the repeater is putting out its CWID, but that wouldn’t be DTMF sounds. Interesting.
 

ecps92

Member
Joined
Jul 8, 2002
Messages
14,360
Location
Taxachusetts
I've also seen repeaters putting out the DTMF to report back the users time on each CTCSS/DCS Tone - reporting back to the Radio shop for billing purposes by use vs flat fees

We had this problem on a public safety system I maintained. Turns out, it was a Kenwood mobile radio that was turned on and off with a battery master switch in an ambulance.

I work with Motorola stuff only, but the Kenwood radio had some features turned on that apparently had a bug or glitch that would cause a continuous DTMF tone until the radio timed out. I don't know what the fix was (different vendor), but the timing of this happening was after a EMS agency was paged for a call, and the crew would get to the station and flip the master switch on...then the tone came out until the radio timed out. When the ambulance was all done at the hospital and getting ready to return to the garage, they would flip the master switch on and...bam...DTMF tone. I could watch it drive around by watching the JPS voter and seeing the different rx sites light up.

If you are programming your own radios, I might suggest disabling all signalling and features you don't need. If it's new enough maybe a firmware update could help.

If you are running Kenwoods, this is what may be happening and not a jammer.
 

kenwoodgeek

Member
Joined
Feb 1, 2015
Messages
218
Location
Wheaton, IL
Thanks for the helpful info, everyone. I'll try to answer all the questions and provide info about our system.

We run all Kenwoods. About 120 of them. The school bus and office/shop mobile radios are NEXEDGE NX-800Hs, TK-8180Hs, and TK-8150s. We have mostly KMC-35 microphones with a few KMC-27s mixed in there. No keypads. As for our office/shop portables, we have 3 TK-3312s, 2 TK-3173s, and 3 TK-380 Ver 2.0s (the 380s I purchased and programmed myself). No keypads on these, either.

ALL of the radios (except for two of the TK-3312s which I haven't reprogrammed) use FleetSync PTT ID. The mobiles do both BOT and EOT, and the portables just do BOT. All the radios originally had FleetSync, but most were programmed with the same codeplug, so the IDs were all the same, and there were selective call alerts off the charts. When I started, I came in and reprogrammed every radio in the fleet with its own ID so we could utilize caller ID on the base radio screen with bus numbers. So all the radios of the same model have the same programming file, with exception to the ID number. I just checked the master files I have for the radios. They all have time out timers set for 60 seconds, which is what they have always been. Since we have many other locations (our neighboring location does some of our routes daily), we do have their radios on our repeater every day.

The tone is just a single tone that starts and lasts for 30 seconds. It sounds like DTMF tone 3. I do know there are plenty of other users on our receive frequency (we always get the wonderful "jackhammer" data sound when the microphones are removed from the clips), but I just looked at our repeater input frequency, and it looks like there are a handful of other agencies in the area using it (one of those, interestingly, is a local Topgolf).

I will fire up my BCD436HP and start monitoring the repeater input. Don't know why I didn't think of that before.
 

ladn

Explorer of the Frequency Spectrum
Premium Subscriber
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Oct 25, 2008
Messages
1,284
Location
Southern California and sometimes Owens Valley
I will fire up my BCD436HP and start monitoring the repeater input. Don't know why I didn't think of that before.
If (when) you find the offending tone on the input frequency, you will then have to do some direction finding and detective work to figure out exactly where it's coming from.
 

RFI-EMI-GUY

Member
Joined
Dec 22, 2013
Messages
6,859
Better yet get some good quality recordings of the sounds on the input and output of the repeater.

The fact that you are sharing the channel with another licensee(s) is a clue that there might be a malfunctioning data transmitter on the channel and you are hearing modem tones instead of DTMF #3.
 

a417

U+0000
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Mar 14, 2004
Messages
4,650
Silly question, but it popped up when you said you get (jackhammer) data noise when you pick up the mic. Are you sure ALL of it is going thru your repeater? If you only hear it when your mic is off hook (and probably open squelch) you could be hearing someone elses' output, and not your repeater. So you theoretically could have DTMF going THRU your repeater, and repeater-output co-channel interference on open squelch. This may be something that will require multiple different approaches at figuring out.
 

kenwoodgeek

Member
Joined
Feb 1, 2015
Messages
218
Location
Wheaton, IL
Yes, I will definitely have my scanner set to record all the inbound transmissions. I'll have to use a recording device to capture the output side from one of my radios at home. Then, hopefully the true detective work can begin. I'll post any updates and audio samples if I can get them.

a417, to answer your question, no. The annoying data bursts are just on the receive side. The radios don't hear them if the mikes are in the clips and the monitors on the radios are off. This tone, on the other hand, is definitely either coming from or through the repeater itself with the 051 DPL. All the radios hear it with the mikes in the clips.
 

a417

U+0000
Joined
Mar 14, 2004
Messages
4,650
You could try enabling off-hook PL decode, that should help a little...albeit you will not be able to hear anyone NOT using the PL, or transmitting in CSQ.
 

riccom

Upstate S.C.
Premium Subscriber
Joined
Jul 2, 2004
Messages
1,318
Location
Kansas City Mo
what school district is this we are talking about, i found one with this
466.35000 WQQU623 M054 DPLCloverdaleESCloverdale Elementary School (Carol Stream) FMN Schools
and this one
16466.3875000011K2F3EMO15004.00041.83061-88.06767GLEN ELLYNDUPAGEIL
 

prcguy

Member
Joined
Jun 30, 2006
Messages
15,228
Location
So Cal - Richardson, TX - Tewksbury, MA
Back when I used Comm Spec TP-38 repeater controllers, they would fail occasionally and transmit a continuous or reoccuring touch tone. I sort of remember having to replace a RAM chip with internal battery or something similar but its been 25yrs since I've used those panels.

One of these TP-38 panels was on a So Cal GMRS repeater that failed and the owners were in no hurry to fix it, so it ran that way transmitting on and off for a few months. Until they learned the FCC visited the site and could not identify the specific antenna and we got word they were going back the next day to positively ID the repeater. One of the system operators got there before the FCC and fetched the entire repeater.

Anyway, you might give us more info on the repeater brand and any accessories connected to it.
 

KK6ZTE

Member
Premium Subscriber
Joined
Mar 27, 2016
Messages
895
Location
California
See R8000's post about the Kenwoods. Our County has the same issue occasionally on their Sheriff and Med channels and they've narrowed it down to the TK-8150 radio fleet. How many 8150s do you have in service and how many have the newest firmware?

Jackhammer sound is a DMR repeater on the same frequency. Ran into that plenty of times.

Thanks for the helpful info, everyone. I'll try to answer all the questions and provide info about our system.

We run all Kenwoods. About 120 of them. The school bus and office/shop mobile radios are NEXEDGE NX-800Hs, TK-8180Hs, and TK-8150s. We have mostly KMC-35 microphones with a few KMC-27s mixed in there. No keypads. As for our office/shop portables, we have 3 TK-3312s, 2 TK-3173s, and 3 TK-380 Ver 2.0s (the 380s I purchased and programmed myself). No keypads on these, either.

ALL of the radios (except for two of the TK-3312s which I haven't reprogrammed) use FleetSync PTT ID. The mobiles do both BOT and EOT, and the portables just do BOT. All the radios originally had FleetSync, but most were programmed with the same codeplug, so the IDs were all the same, and there were selective call alerts off the charts. When I started, I came in and reprogrammed every radio in the fleet with its own ID so we could utilize caller ID on the base radio screen with bus numbers. So all the radios of the same model have the same programming file, with exception to the ID number. I just checked the master files I have for the radios. They all have time out timers set for 60 seconds, which is what they have always been. Since we have many other locations (our neighboring location does some of our routes daily), we do have their radios on our repeater every day.

The tone is just a single tone that starts and lasts for 30 seconds. It sounds like DTMF tone 3. I do know there are plenty of other users on our receive frequency (we always get the wonderful "jackhammer" data sound when the microphones are removed from the clips), but I just looked at our repeater input frequency, and it looks like there are a handful of other agencies in the area using it (one of those, interestingly, is a local Topgolf).

I will fire up my BCD436HP and start monitoring the repeater input. Don't know why I didn't think of that before.
 

kenwoodgeek

Member
Joined
Feb 1, 2015
Messages
218
Location
Wheaton, IL
Thanks for the advice. I don't have off-hook decode set on the radios just to keep things consistent and the programming files as close to the way they were before. It's not that bad. I tell people who complain about the noise to suck it up.

No, we are Illinois Central School Bus in Carol Stream. 463.2625 with 468.2625 repeater input. D074N DPL tone.

Thanks for that info about the repeater components. I don't service the repeater, so I don't know anything about it. Never even seen it, actually.

We have only 14 TK-8150 units in service. A few of them have been in service since at least 2011 with, as far as I know, no updates ever done to them. Some of them, I'm sure, are running firmware that is outdated as heck. I'll run through the lot and see if I can check the firmware versions on each of them.

I will also report that today's recording session was a fail. It happened this morning. I had my scanner back at base recording the input frequency, but going back and listening to it, nothing. So, if this is an external transmission, it was not close enough for my scanner to pick it up.
 
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