Has anyone else noticed a strange noise at the end of transmissions lately? I've been a listener for over 25 years and it's something I've never heard before. Anything to do with the changeover that's coming? I really can't explain what the sound is. Just something different.
NYPD CW 2
- Thread starter coolrich55
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Can you explain a little bit more what you heard? I’ve been listening and haven’t heard anything different or unusual. What you maybe hearing is the MDC1200 ID being transmitting from the VX-P824. It sounds a little different transmitting from these radios than it does from the other radios.
Danny37
Member
Same here, I dont notice anything different. 4-crime is probably right, Its probably that courtesy tone after the mdc1200 from those 824 radios that are still around.
Danny37
Member
Haven't heard anything yet. Back in 2019, it was said to be 3-5 years... so we are coming into that timeframe soon.
It’s a tone remote from the voting comparators not the radios themselves… 99.9% of public safety dispatch consoles are 4-wire systems… meaning they can listen and transmit simultaneously… look up tone remote on Wikipedia… those are a little more then just regular courtesy tones… there’s a 2150Hz tone u hear and then a sub-audible carrier tone then a lower frequency audible ending tone
It’s actually 2175 Hz and it is not sub audible. Tone remote uses the sequence of 2175 then 1950 then 2175 low level guard tone. The 2175/1950 keys the transmitter and the 2175 LLGT keeps the transmitter keyed.
Yes it is a 4 wire system but the comparator has a console priority card installed. That’s why the dispatcher can talk while still hearing field units.
Yes it is a 4 wire system but the comparator has a console priority card installed. That’s why the dispatcher can talk while still hearing field units.
Yeah I I meant the 2175hz first then the middle one is the subaudible carrier correct?
Standard tone remote control is 120ms of 2175 at 0 dBm, 40ms of 1950 at -10 dBm and then continuous 2175 at -30dBm during the transmission.
Old manuals may specify the levels as +10/0/-20 for wireline control circuits but fiber or digital circuits can't take levels over 0 dBm input.
An audio filter filter removes the 2175 during the transmission but the high level 2175 key up tone and the 1950 function tone may bleed through. There is no "end tone" but you may be thinking of the Reverse Burst or Squelch Tail Elimination tone used in older CTCSS systems where a burst of the tone was sent out-of-phase at the end of transmission to kill the squelch tail.
You normally don't hear the key up tones because the transmitter does not key up until the function tone is decoded. But if the transmitter is already keyed from one source and another remote keys up you will hear the keying tones.
Now question… by no means I would ever intentionally commit an illegal act and I’m never condoning such….. but for example what if a portable keys up with the same tone encode pattern of the remote?
That's not how it works. The tones are for direct wireline control of a repeater, not over the air. Keying up on a repeater input will key up the repeater regardless.
So if a portable is programmed with the same exact freq/timing of tones it’s just gonna sound like a a tone remote soup sandwich? 😂 😂 😆
If the portable sends the tones after the repeater is already keyed it may or may not be audible over the air. It might even cause the audio to cut out during the tones. Some receiver voting systems use similar tones to indicate an idle condition. GE used 1950 and Motorola 2175 on some versions of their voters so the tone would cause the voting selector to mute. And, the 2175 tone is filtered out of the TX audio so you only may hear the bleed over if the tones are sent at a vey high audio level. If someone wanted to be disruptive this would only be a minor noise nuisance compared to other possibilities. There are different scenarios depending on if the system is just a normal repeater or it is a receiver voting system with the voter tone keying the transmitter. In any event, it is unlikely to effect any system control function. It will only be one more type of annoying noise.
902
Member
There are also situations where the gain from the console priority card is cranked very high and the audio bandwidth limiting may "ring" and heterodyne with the 2175 creating what sounds like a 1450/1950 sequence (or very close). It's still 2175. If multiple keying logic has the repeater keyed, or has a hang-time set, the keyup sequence might be heard. Then, there is another variant of tone remote control that inserts a second function tone that toggles coded vs. clear. It sounds a little like tone remote, but with an extra tone in the sequence. But that wouldn't make sense in newer generation equipment.
If it's new equipment and there's a focus toward digital, why would it not use DFSI and a digital comparator rather than any of the old analog control stuff?
Instead of guessing (and probably guessing wrong), can someone post a recording of it? There are a lot of professional radio people in the group who can identify it.
If it's new equipment and there's a focus toward digital, why would it not use DFSI and a digital comparator rather than any of the old analog control stuff?
Instead of guessing (and probably guessing wrong), can someone post a recording of it? There are a lot of professional radio people in the group who can identify it.
Tone remote is very critical on audio levels so many glitches are possible but usually not from anything in received audio. I had a case of a system that used a non-standard function tone for F2 that triggered the telco equipment on the lease line into loop back whenever they tried to use F2 TX.
This will all be moot once a system goes digital and NYPD probably already has something newer than SpectraTac technology now in preparation for the changeover.
So any adjustments are essentially done the same way u adjust settings on your home router
Wow no wonder a tone remote Costs so much $$$$ … most people just think it’s a courtesy tone lmao
902
Member
Tone remotes are a niche product. Compared to 30 years ago, there are a handful of manufacturers that work with it, and much of the legacy products were deadlined with narrowbanding. I just bought a few VTE-1 voting tone encoders to use with an analog comparator I had sitting on a shelf. The costs were fairly reasonable, all things considered. The big problem is maintaining audio characteristics from the receiver to the comparator. So long as there's an acceptable bit error rate, that's not as much of a concern in digital.
12dbsinad
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Biggest problem with tone remote other than dealing with leased lines BS is 2 tone paging. There are certain paging tones that simply will not work, it’ll just dump the transmitter. Can’t tell you how many times “radio companies”
Couldn’t figure out the problem in my area.
Couldn’t figure out the problem in my area.
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