Unknown data is falsing receivers

[Wile E. Coyote]

For the last few months, we have been hearing this data on our frequency (156.210):

http://WEC.fileave.com/Recorded%20on%20 ... 68237).WAV

The data burst at the end is falsing our receivers that have a PL of 131.8. We listened for a station ID, and none was found. I've even tried monitoring it with a P25 radio, and it didn't decode.

At this point I'm just curious what it is! Maybe if I can find out what kind of data it is, that might help me narrow in on the source.

Any thoughts?

~WEC

[Will]

Sounds like the dreaded 'Motorola trunking honk'

[Pj]

I've heard that with voice pagers running on VHF and UHF. Usually some data here and there with that noise, then once and awhile your will hear a voice message. Not as common as they once were but still around. I forget what services use to market it.

Back in the scanner days, most were business or medical/hospital related. Some hospitals still use it for campus/internal paging.

Depending on where in DV you are, and I am guessing VHF, I'd say look towards China Lake or Mojave as IIRC, they were implementing VHF trunked systems. SBCO is all 800, Kern is VHF fire/UHF SO, and I think Tulare is very simple VHF. Not sure whats on the NV side, but I think there is OpenSky running with a water authority. Not sure what band they are running on though. NV has a statewide MA/COM system and I have heard similar sounding data with an older EDACS system.

My best guess.

[Wile E. Coyote]

PJ - My apologies. The location in my profile is fake to keep my boss from a previous employer from knowing what I was talking negatively about the company. I used DV in honor of my Great Uncle who lives in Palmdale, and used to be a test-flight engineer at Edwards during the 50’s & 60’s. (A few months ago we went down into Mohave to check out the space port. There is some weird stuff going on there).

Actually, I live in Des Moines. Iowa.

FYI, I did check to see if the sound we are hearing matches any of the raw data samples from this page: http://www.kb9ukd.com/digital/ - Nothing. I forwarded the sound on to some engineers at Mother (M) through a friend of mine, and they have no clue either.

[Wowbagger]

Well, the sample rate's a little lower that I would have wished, but it looks like some form of 4 level modulation. If I don't miss my guess, the baud rate looks to be about 3000-3600 baud. Maybe FLEX paging?

[tvsjr]

Definitely not FLEX. It lacks the periodic near-constant tone heard with FLEX, used to divide the phases.

[motorola_otaku]

I have heard that before.. in the Fed VHF band on WHCA/USSS frequencies. I always assumed it was Type 1 encryption, but I don't think even it can carry a PL with it.

Something else that might be a possibility is someone else's broken repeater is picking this up from God knows where and rebroadcasting it on your frequency with your PL.

[Wile E. Coyote]

...I always assumed it was Type 1 encryption, but I don't think even it can carry a PL with it.

I thought it might be encryption, but it is not like any I have heard before. As for the data itself, there is no PL on it. The "sync pulse" at the end just happens to pulse at the same frequency as our PL, so all we hear coming through is the data burst at the end. Still very annoying. We just opened the squelch long enough to get a half way decent recording of it to share.

Also, the signal level in our area is very weak on the ground. When we monitor it from a tower mounted antenna, we see it at around -90dB.

Another piece to the puzzle is that we don't seem to hear it when it's raining. Road crew maybe?

[Pj]

Anyone know what the GPS survey machines are running? I remember Station House had a problem with the data radios playing havoc with some repeaters a few years ago. I want to say it was UHF, but could have been VHF.

[Rayjk110]

464.550 and 469.550.....


Sometimes MURS but not that common.

[xmo]

After listening to your file on my home computer where I have better speakers than the ones in the flat panel display at work, I am pretty convinced that you are hearing the output of a P25 repeater.

I really never listen to my VHF repeater [Quantar] in analog mode since it isn't set up for mixed mode, but I have done so tonight and it sounds like what you have recorded.

Your inability to monitor it with a P25 radio might be because of a NAC mismatch, or secure coding of the transmission, or what you are hearing may have been repeated onto your frequency through an analog device - for example an analog vehicular repeater and thus become too distorted for a digital radio to decode.

[Hartley]

Hi,

I agree with XMO - that sounds a whole lot like what a Quantar in "mixed mode" does when it repeats a P25 signal - the burst at the end is just the "tail".
You may need to use DF to figure out who it is..

Hartley

[xmo]

Another possible reason why you don't hear anything when you monitor with a P25 radio is that the signal may contain data rather than voice frames. I think the State boys [DPS & DOT] have that ability so you might check with their radio guys.

[Wile E. Coyote]

...You may need to use DF to figure out who it is..

That's cool. At least now I think I know what I'm working with here.

Can I assume that “DF” means Direction Finder?

[edit]

XMO - The state guys were some of the first we contacted. They claimed that they have no clue what it is. In fact, they have had poor performance on one of their other channels, 156.025. We just recently found out that the same data sound is on that frequency as well. the plot thickens.

[/edit]

~WEC