WNC 406.9125?

waterbwuk

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Anyone have any idea what this may be? It seems to be a constant signal that has two beeps every 12 seconds. Every once in a while (it's not on a set timer like the two beeps), there is a burst of something. It can be heard about 25 seconds into the attached recording. I also attached a waterfall picture of when that burst occurs.

I've spent a while looking through sigidwiki and haven't come across anything that exactly matched up. The closest was P25 P1 Encrypted Voice Bursts (Found here at the bottom under Additional Samples), but I don't think that is it.

87879
 

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kd4efm

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Florida, we have seen this and belive its DMR tier 3 repeater being used by USPS, being 406.9125, which is federal.
We are also trying to see if it could possibly be coming from a jstars when they are airborne too.

Just a hunch.
 

waterbwuk

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Florida, we have seen this and belive its DMR tier 3 repeater being used by USPS, being 406.9125, which is federal.
We are also trying to see if it could possibly be coming from a jstars when they are airborne too.

Just a hunch.
Interesting, I only see one DMR Tier 3 (apparently DSD+ identified it as one) recording on sigidwiki and it's under unidentified signals, doesn't have any beeps like this one though. I don't really know much about DMR but would it be a control channel? I tuned into a DMR CC frequency in my area and it sounds about what I would expect from a CC.
 

Airboss

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Not knowing where in NC you are located I cannot say for sure. If you are within radio range of Mt Mitchell there is a P25 link on 406.9125 as part of the UHF backbone for the Blue Ridge Parkway. It links Mitchell to Cowee Bald with the duplex pair on 415.9125. It is used to link 172.725 MHz repeater on Mt Mitchell.
 

kj6psg

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I've heard these before! These were on 406.9125, 408.9125, and the opposite side of the pairs at 415.9125 and 417.9125.
Here, USFS (specifically, Angeles NF) used them for repeater links. I think it's some kind of mixed-mode wireline operation (P25 & analog) over what would normally be a leased line, but is here a RF link. They got rid of these back in 2019ish, and the links are now mixed-mode P25 and analog.

Typically, three sets of data were transmitted at a time, with those tones before each hunk of data. The data was different each time even though the channels were idle. The data would interrupt when analog voice came on, not sure about digital voice behavior. Never did find out the modulation, but someone pointed out it sounded like V.29. I'd have to dig up a sample of that, but in the meantime here's some voice traffic while the idle link was sending continuous data. I've also heard the two-beeps before, but rarely.

[edit] Someone on YouTube uploaded a sample back in 2013 of what I'm trying to describe.
 

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waterbwuk

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Not knowing where in NC you are located I cannot say for sure. If you are within radio range of Mt Mitchell there is a P25 link on 406.9125 as part of the UHF backbone for the Blue Ridge Parkway. It links Mitchell to Cowee Bald with the duplex pair on 415.9125. It is used to link 172.725 MHz repeater on Mt Mitchell.
Interesting, I didn't know that! I'm all around the area but this one I picked up within about 20-30 miles of Mt. Mitchell, so that would make sense. Thanks for the information.
 

YalekW

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I have a bunch of info regarding this signal.
This (was) a special signal in use in Los Angeles' National forest for their park management. It possibly used a DIU3000 + X437A combined option, but this is only according to my fellow friend Notipa.

The modulation is quite confusing because it appears to give off a V.29 modem modulation, as thats heavily used in fax machines. However, this is not the case.

Most V.29 modems over radio are used as Glenayre paging link's (the QAM noise), such as 454.425 in Chicago IL with license KNKH915, but this is not it.

This is what he had told me regarding this funky thing while DM'ing him over discord:

"Quantar/Quantro repeaters don't actually parse any vocoded traffic due to licensing, the DIU is basically an XTS3000 with no RF stages that converts between analog and IMBE."

"the repeater just checks whether it's receiving a digital signal, then retransmits whatever it hears if it meets unmute criteria (PL/DPL match, NAC match, signal strength)".

I dont know if these findings are correct, but it sounds pretty intriguing.
 
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waterbwuk

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Did you ever get a NAC or PL Tone ??
Nothing at all. Signal was still active last time I checked. When I first noticed the signal, it was the weekend so I expected little to no traffic, but later I tried again to monitor it over a couple of different weekdays and the signal never really changes. I've tried to decode it every way I know of using things like rtl_433, multimon-ng, PDW, etc and got nothing. About the only thing I haven't tried to do is set it up as DMR and that's only because I know nothing at all about DMR.
 
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