Bursts of noise on channel 15

[WRTC928]

For several days, I've been receiving bursts of noise which sound similar to the old dial-up modems but faster and with more static. It seems to be random in when it starts, but when it does, there will be a burst about every 45-60 seconds for maybe 15 minutes and then it stops. I initially heard it on my repeater frequency (channel 15), and I thought perhaps my repeater was causing it. I heard it on simplex 15 as well, but a simplex channel with no tone engaged will hear repeater output. However, I turned my repeater off, and it continued to happen, so it's not due to anything I'm doing. The thing that puzzles me is that with a radio set to my repeater frequencies and receive tone engaged, I shouldn't be able to hear anything that doesn't use that tone, but I do. Can anyone enlighten me as to what may be causing this?

[WRTC928]

13 minutes ago, SteveShannon said:

With a 30 second period it sounds like it’s part of some signaling system.  For a while various devices were sold that used FRS/GMRS frequencies for non personal radio purposes.  Baby monitors, home weather stations, etc.  Perhaps it’s something like that.

Nothing prevents transmitting multiple CTCSS tones simultaneously with strings of data that include DTCSS codes, especially if those codes are being used to carry other data rather than access codes.  Because they’re very short and audible CTCSS tones and DTCSS codes are extremely simple to inadvertently include in a transmission if a transmitter isn’t explicitly filtering them out.  Our radios do that; they intentionally filter them out before adding specific ones in while transmitting.  Someone’s home control system easily might not.

Given the fact that you are able to anticipate when it’s going to be heard you should be able to track it.

That makes sense. 

[WRTC928]

18 minutes ago, WSGL775 said:

This sounds like a text message being sent via rattlegram from a phone through the radio. We do it all the time when we are in a tactical mode, but encrypt the transmission with AES 256 so we know no one can break the code without the master key. Just an observation.....

Would that go on for more than an hour?

[MarkInTampa]

You could try to use ARTEMIS Offline Signal Identification to identify it. Download at ARTEMIS Download . Set a filter to 462MHz to listen to signal samples known (76 at the moment) to be available in the band, click through them and listen to the audio sample and hopefully you will find a match. Listen in particular to the samples of the obvious choices first - NXDN, DMR, P25, Motorola. Ignore obvious ones that are not relevant in the US like NMT, PAL, RTS-9TS, etc. Here's a Techminds video of how to use ARTEMIS: https://www.youtube.com/watch?v=W_8Y_4FvoHI