Public Safety Repeater Alert Beep

[UnHumanReactions]

My local police department uses a repeater for their radios and whenever a unit starts transmitting, there is a short little beep, almost like an alert tone to let people know to listen to the radio. It's not the MDC-1200 data burst, it's right before it. It also happens when the dispatcher starts transmitting. There is also a two tone beep that happens when someone starts transmitting before the repeater stops, which can also be heard in the audio clip. I'm interested to hear what other people think of it. I have never heard it anywhere else except for my local police department's repeater.

Here's the link to the sound clip with the beep: https://www.youtube.com/watch?v=_srWG7YmaZo&feature=youtu.be

 

[W8RMH]

It sounds like the radio sending the radio ID number. Depending on the radio model some tones are audible while others are not.

 

[RFI-EMI-GUY]

The short 2175 Hz beep is part of the tone keying burst, (2175 Hz high level guard tone, 1950 Hz Function Tone, followed by continous 2175 low level guard tone. A portion of the high level guard tone escapes being muted by the repeater. The voter also sends these tones when a mobile transmits. The data bursts from the mobiles are MDC1200 signalling, they represent the unit ID of the mobile. The mobiles don't hear these tones if the Data Operated Squelch is programmed.

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[krazybob]

It sounds like MDC 1200 without data muting. It could be mixing in with the tone remote. The additional beeps may indicate the remote receiver that is hearing the unit the best. I'm not aware of any scanner that has data muting. Salinas uses 11.3KHz narrowband and operates off of one transmitter site that's probably using brute force transmitter power to cover their entire area and satellite receivers to fill in on the fringe areas. They're doing 75 watts from the mountain right above them which is quite high power. My repeater does 100 watts and covers 7 counties. I suppose part of that is to accommodate HT performance. Public Safety operates on a 95% coverage area. Let's read with more knowledgeable people have to say.

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[UnHumanReactions]

Thanks, all you guys for replying, but just so I am more clear, I uploaded another clip of the exact part I'm talking about. Some said that it was the MDC-1200 but it can't be since it also can be heard when a normal radio, without MDC-1200, transmits. The dispatcher radio doesn't have MDC-1200 and the beep can still be heard. I've also included the "two tone" beep that can be heard right when the repeater is about to stop but another radio starts transmitting again.

Here's the link: https://www.youtube.com/watch?v=5ZI3_y9i1LQ&feature=youtu.be

 

[firefive76]

Read post #3. This is part of the keying process in a voting system most likely.

 

[krazybob]

Yes but what does it sound like on a Motorola? As I said although I'm no expert in this does not really sound like MDC 1200. It sounds more like control tones. Dispatch often uses a radio console that transmit over the input to the repeater site. It's not uncommon to have 3 or 4 remote receive sites throughout even a small City and I'm guessing the tones may very well be steering tones that identify which remote receiver is picking up the unit. I'm not sure why since Salinas is not digital and they are relatively small town.

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[rescue161]

Yes but what does it sound like on a Motorola? As I said although I'm no expert in this does not really sound like MDC 1200. It sounds more like control tones. Dispatch often uses a radio console that transmit over the input to the repeater site. It's not uncommon to have 3 or 4 remote receive sites throughout even a small City and I'm guessing the tones may very well be steering tones that identify which remote receiver is picking up the unit. I'm not sure why since Salinas is not digital and they are relatively small town.

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It sounds exactly the same on a Motorola as these are not MDC bursts. See post #3.

On a side note, my base station is set up using a tone remote (MC2500) to control 4 different radios with 15 channels each. If I quick-key the radio via the MC2500, users will hear the 2175/1950 tones go over the air. It also makes for a clean setup as I don't have 4 radios in front of me. They (the radios) are all about 275 feet away in another building.

 

[krazybob]

I left my thoughts about tone remotes out so as to not complicate the response. But that's exactly what I thought. The base station is keying up with tone remote and it's being picked up and needed by the repeater. I did specifically mention voting.

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[ffexpCP]

I concur- certainly keying tones. You will most likely hear them when someone keys up while the repeater is still up from a prior transmission with the delay / hang time timer. Otherwise, the tones are too short and not heard while the repeater is still responding to the command.

The others are MDC PTT ID. Specifically IDs B359 and B375.

 

[ramal121]

As mentioned in a voted system the transmitter is keyed by tone control whether it is from dispatch or a field unit through the repeater. Normally you would not hear the tones (except under certain conditions) as the transmitter keys up after the high level and function tones pass.

If you are not changing channels as is the case with a repeater, you can configure the transmitter to begin keying on high level guard tone. This slightly reduces the delay to bring the repeater up however it will let the function tone slip through every time. Since the function tone is not notched it is heard loud and clear.

This is different that the MDC burst that follows this from the field radios.

 

[RFI-EMI-GUY]

Thanks, all you guys for replying, but just so I am more clear, I uploaded another clip of the exact part I'm talking about. Some said that it was the MDC-1200 but it can't be since it also can be heard when a normal radio, without MDC-1200, transmits. The dispatcher radio doesn't have MDC-1200 and the beep can still be heard. I've also included the "two tone" beep that can be heard right when the repeater is about to stop but another radio starts transmitting again.

Here's the link: https://www.youtube.com/watch?v=5ZI3_y9i1LQ&feature=youtu.be

On that second video, there are no MDC1200 tones, just quick keying of the console or voter, and on some transmissions, both the 2175 Hz HLG tone and 1950 Hz Function Tone are slipping through. This is because the Function tone mute timer hasn't been given time to reset. The Function Tone is used normally, to set the F1 channel in the repeater station. If any different channel is set , that tone might be 1850 Hz or any of several variations. My ear is telling me it is 1950 Hz in the video.

If you listen carefully on a mobile unkeying, the voter will leak through a weak burst of 2175 HZ (if Motorola SpectraTac), tone that is also used to indicate that a satellite receiver is idle. The function of the 2175 Hz tone is also used to lock the AGC in the voter.

There are 2175 Hz notch filters in the console receive audio and the repeater transmit audio to eliminate this tone, but it is innefective on the High Level Guard tone, and the lower amplitude tone from the voters still gets through.





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[UnHumanReactions]

Thank you. This has been very helpful.

 

[krazybob]

I actually tried to avoiding getting that deep into tone remotes, but yep. Keep in mind that the dispatch console may have a tone remote going to a radio in the building. It's not uncommon. That allows them to avoid a microwave link or or even a radio link to the transmitter site. I know of numerous police and fire department's down here in the south that do it just that way. Essentially they have a mobile unit that is used to transmit to the repeater site. I could be completely wrong on this and they actually have a microwave link to the repeater site. Not according to their license.

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[rescue161]

Usually a dispatcher is using 4-wire tone control that is wired directly to the repeater, either by microwave or dry pair or other means. This allows the dispatcher to talk and listen at the same time. So if they are keyed up, they can still hear units that need help.

Mine is set up as 2-wire as I'm not connected directly to the repeater.

 

[RFI-EMI-GUY]

Usually a dispatcher is using 4-wire tone control that is wired directly to the repeater, either by microwave or dry pair or other means. This allows the dispatcher to talk and listen at the same time. So if they are keyed up, they can still hear units that need help.

Mine is set up as 2-wire as I'm not connected directly to the repeater.

Right, that is console wireline priority. The dispatcher audio takes priority over mobile repeat. The dispatcher always hears what the mobiles are saying. In high speed chases, sometimes the dispatcher will relay to following units, what the pursuing mobile is reporting.

Where there is no wireline, or microwave connection to the repeater, RF control stations are used, and then the dispatcher has no priority over the mobiles. It is not ideal. But sometimes RF control stations are a fall back mode in case of microwave or telephone circuit failure. In other cases, small substations or rural departments rely on RF control stations because it is most cost effective solution.

There is a lot of variation in system design.

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[krazybob]

Yes they are usually set up that way but not always. You can look at our Sheriff in the San Bernardino Mountains who simply have a Motorola Astro Spectra on a power supply. Or Arcadia Police Department that before they went to ICIS had a mobile unit in the radio room and a tone remote. Their repeater site is a top Johnson Peak at 3200 feet above the city. No microwave to the site - simply a dispatcher with a mobile radio running through Centracom .

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[RFI-EMI-GUY]

Yes they are usually set up that way but not always. You can look at our Sheriff in the San Bernardino Mountains who simply have a Motorola Astro Spectra on a power supply. Or Arcadia Police Department that before they went to ICIS had a mobile unit in the radio room and a tone remote. Their repeater site is a top Johnson Peak at 3200 feet above the city. No microwave to the site - simply a dispatcher with a mobile radio running through Centracom .

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I am from the flatlands in Florida, where 99% of the systems are 800 MHZ trunked, wireline control, simulcast. A lot of money spent with Motorola/MSI and GE/COMNET-MaCom/Erricson/Harris! No high mountains to blast from, nor valleys of darkness.

About 8 years ago, I did an interoperability study project in the California Central Valley. I got to see about seven counties worth of VHF and UHF systems. They ran the gamet from Kern County that was then on its sixth highly tuned generation of Simulcast, to an intentionally unnamed City where I met the poor exhausted technician who apologized for having been up for 72 hours straight patching the VHF repeater back together from 3 different MSR2000 cabinets. The transmitter in one, the receiver in another, and the power supply in the third. No kidding, I asked him which cabinet was the main dispatch channel and he waved his hand over all three cabinets and showed me all the cabling he had just patched the working 1/3 of each together.

I commented that it appeared there were BRAND NEW consoles, CAD and 911 call taker positions in the adjacent dispatch center. He said yes, but the IT Director still doesn't understand radio and he controls the budget! I noticed the pitiful repeater antenna was on an ancient wooden phone pole. As long as this technician played magician, no radio upgrades were being done, not even with narrow banding considered. I felt for the guy.

While this city was the worst in terms of RF infrastructure, it did set the tone for the report that OPERABILITY was a key element to inter-operability. My recommendations for many of the Counties was for wide area tactical channels, requiring voters and in some cases simulcast. Some counties relied on a myriad of stand alone repeaters, often on the same channel and activated by a PL tone selection, in order to fill in the valleys. It must truly be challenging for radio operators to keep track of the system during major incidents.

I got to visit some outstanding mountaintop repeater sites, some very well designed, others, were a throwback to installation practices of 35 years ago.




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[KevinC]

I am from the flatlands in Florida, where 99% of the systems are 800 MHZ trunked, wireline control, simulcast. A lot of money spent with Motorola/MSI and GE/COMNET-MaCom/Erricson/Harris! No high mountains to blast from, nor valleys of darkness.

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You left out Tyco.

 

[krazybob]

We call that poor man's voting. It's actually commented amateur radio. Not with me because I prefer rslinx over internet links. I'm an internet professional and trust that the internet is up 99.999 percent of the time but when the big one hits that certainly won't be true. Microwave is great but when the big one hits those antennas are going to be out of alignment you can be certain. But back to the point. I think we have determined just as many of us thought that what is being hurt at the beginning are the tone remote signals being sent along with the unit identifier. It doesn't sound like an MDC 1200 either. But I'm no expert on MDC. Some of you guys have just given me a pretty good education.

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