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?

[WRUE951]

Sounds like you are picking up digital transmissions from nearby source. I.e.:

• DMR Activity: You might be hearing Digital Mobile Radio (DMR) signals, which sound like a buzz or "machine gun" noise on an analog radio.
• Other Digital Signals: There are various other digital radio signals that can bleed over or interfere with GMRS frequencies and could be generated from nearby public safety digital radios. I.e police dept. 
• Utility Use: Some digital signals are telemetry data or other utility uses that might be operating on or near GMRS frequencie

you might want to invest in a Tiny Spectrum Analyzer which will help you with frequency and pinpoint the source.   Lots of you tube videos out there for Tiny Spectrum Analyzer 

[OffRoaderX]

5 minutes ago, WRUE951 said:

Sounds like you are picking up digital transmissions from nearby source

This is what i was going to say, but it does not explain why/how its opening his squelch/getting past the RX tone he has set.

[dosw]

Live near a hospital?

 

I got an MRI a couple of years ago, and as I approached the facility and drove away from it, channel 17 was picking up the exact sound I was hearing while inside the MRI tunnel.

 

Otherwise I'd guess DMR or some other digital signal. My SDR is particularly good at letting DMR on nearby frequencies intrude into what it picks up in the GMRS band.

[SteveShannon]

6 hours ago, WRTC928 said:

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?

Instead of a receive tone engaged, try setting a receive DCS code in your radio to see if it still receives it.   Noise can include several CTCSS RX tones but might not so easily mimic a DCS code.

Have you tried listening to other channels that are adjacent to channel 15?  Channel 1 is the closest of the GMRS frequencies at 462.5625 MHz.  Channel 16 is at 462.575 MHz and then channel 2 is 462.5875 MHz. This might help you see how broad the bandwidth of the noise is.  If it’s truly random noise it might be pretty broad, but if it’s a digital signal it should be fairly narrow.  A spectrum analyzer like @WRUE951 suggested would be helpful also.

Does it still happen away from your house or if your main breaker is open?

Try recording the audio for a few seconds and post it to this thread.  

[WRTC928]

2 hours ago, SteveShannon said:

Instead of a receive tone engaged, try setting a receive DCS code in your radio to see if it still receives it.   Noise can include several CTCSS RX tones but might not so easily mimic a DCS code.

Actually, the receive code I'm using is DCS. 

2 hours ago, SteveShannon said:

Have you tried listening to other channels that are adjacent to channel 15?  Channel 1 is the closest of the GMRS frequencies at 462.5625 MHz.  Channel 16 is at 462.575 MHz and then channel 2 is 462.5875 MHz. This might help you see how broad the bandwidth of the noise is.  If it’s truly random noise it might be pretty broad, but if it’s a digital signal it should be fairly narrow.  A spectrum analyzer like @WRUE951 suggested would be helpful also.

 I typically have one side of my base or mobile radio scanning, and so far, I've only picked it up on 15. Because of how random it is, it's possible I've just missed it, but that seems unlikely. Nevertheless, I'll set a radio to GMRS 1 and see if I pick it up there too. 

2 hours ago, SteveShannon said:

Does it still happen away from your house or if your main breaker is open?

I don't remember if I've heard it when I'm away from the house. I'll try to find out.

[WRTC928]

8 hours ago, WRUE951 said:

Sounds like you are picking up digital transmissions from nearby source.

That was my first thought. However, in order to be heard on my repeater channel, wouldn't it have to open the squelch? I have a DCS receive code on my HT, but I hear it anyway. Could there be some sort of electronic signal that can be heard despite the DCS code?

[WRTC928]

8 hours ago, WRUE951 said:

you might want to invest in a Tiny Spectrum Analyzer which will help you with frequency and pinpoint the source.   Lots of you tube videos out there for Tiny Spectrum Analyzer 

I might do that if it goes on for a long time or becomes more frequent. TBH, my primary concern was that my repeater might be causing it. Now that I know it isn't my fault, it's primarily a matter of intellectual curiosity. 

[WRTC928]

7 hours ago, dosw said:

Live near a hospital?

 

I got an MRI a couple of years ago, and as I approached the facility and drove away from it, channel 17 was picking up the exact sound I was hearing while inside the MRI tunnel.

The nearest hospital is a couple of miles away, and it doesn't have an MRI machine. Small town Oklahoma.

7 hours ago, dosw said:

Otherwise I'd guess DMR or some other digital signal. My SDR is particularly good at letting DMR on nearby frequencies intrude into what it picks up in the GMRS band.

Would I pick that up despite having a DCS code set? Obviously, there's something that can cause noise on that frequency regardless of the code, but I'm puzzled about what it could be.

[WRUE951]

10 hours ago, OffRoaderX said:

This is what i was going to say, but it does not explain why/how its opening his squelch/getting past the RX tone he has set.

i've noticed, when i have the repeater set with a PL, that i can open my repeater sometimes with a HT programed with no PL tones when in very close proximity to the repeater . .  And it doesn't always happen..  I have also listened to other repeaters with PL's where someone talking on it claim they are operating with no PL's.    So yea, good point but i don't know???  Possibly the sensitivity of his squelch?  

[WRUE951]

2 hours ago, WRTC928 said:

That was my first thought. However, in order to be heard on my repeater channel, wouldn't it have to open the squelch? I have a DCS receive code on my HT, but I hear it anyway. Could there be some sort of electronic signal that can be heard despite the DCS code?

try playing around with your squelch sensitivity setting.  

[WRTC928]

2 hours ago, WRUE951 said:

try playing around with your squelch sensitivity setting.  

I'll try it, but it's happened on three different radios. It seems unlikely they'd all be suffering from inadequate squelch. Still, even if it doesn't stop it, it's a piece of information that may help figure out what it is.

[WRTC928]

8 hours ago, SteveShannon said:

Instead of a receive tone engaged, try setting a receive DCS code in your radio to see if it still receives it.   Noise can include several CTCSS RX tones but might not so easily mimic a DCS code.

 If it's some sort of digital interference, maybe the opposite would be true. Maybe it can slip through a digital code but not a subaudible tone. I'll try setting a CTCSS receive code on channel 15 on a radio and see if that blocks it.

[SteveShannon]

1 hour ago, WRTC928 said:

 If it's some sort of digital interference, maybe the opposite would be true. Maybe it can slip through a digital code but not a subaudible tone. I'll try setting a CTCSS receive code on channel 15 on a radio and see if that blocks it.

Great idea!  That makes sense. 

[LeoG]

16 hours ago, OffRoaderX said:

This is what i was going to say, but it does not explain why/how its opening his squelch/getting past the RX tone he has set.

If it's modem style noise that tone might actually be in there randomly and open up the squelch.

I have a DMR signal that breaks through a DCS RX tone on occasion on 625 which is very annoying.  I have my own repeater with a DCS tone for the repeaters TX (radio RX) and don't have the problem.  So either the DMR transmit has that tone or somehow the DMR signal is activating the radio to open squelch.

Very annoying.

[WRTC928]

3 hours ago, LeoG said:

If it's modem style noise that tone might actually be in there randomly and open up the squelch.

I have a DMR signal that breaks through a DCS RX tone on occasion on 625 which is very annoying.  I have my own repeater with a DCS tone for the repeaters TX (radio RX) and don't have the problem.  So either the DMR transmit has that tone or somehow the DMR signal is activating the radio to open squelch.

Very annoying.

Good thinking! It didn't occur to me that a digital signal might coincidentally contain my DCS code.

[WRTC928]

It's happening again right now, and it is coming through on channel 15 with no codes set, channel 15 with a CTCSS tone set, and my repeater channel with a digital code set. Very mystifying. I haven't heard it all day until now. I'll start making notes to see if it usually occurs at the same time in the evening.

[LeoG]

Mine happen at any time during the day and night.  Usually more during the day.  Seems to wane at night and weekends so I think it's more business related than anything else.

It makes it very hard to use my scan function because it gets stuck on the noise even when it's squelched.