Empty transmissions blocking out multiple frequencies

[Blaise]

GMRS in my area is pretty rarely used.  I scan in the car and when I'm at my desk, and pick up one or two conversations a day max. 

However, a few months ago, I started picking up digital transmissions on .600(17).  They would last anywhere from one to thirty seconds each, and I would pick up clusters of them that would preclude any other use of the frequency for up to an hour.  A few weeks ago, those stopped completely, to be replaced with what seems to be a strong signal nearly continuously transmitting nothing but some static.  In the last few days, these 'nothing' transmissions have begun on .675(20) as well.  They now render both frequencies completely unusable for significant chunks of every day.

Any of you experienced folks have any idea what might be going on? I got a video of my monitoring unit while it was happening.  Not sure if hearing the transmission is useful, but at least you can see for yourself!

[Lscott]

What kind of radio are you using? This could be important.

Also have you tried a different model radio and see if you get the same results?

You could be experiencing an "image response" where the signal isn't really on the frequency you think it is. I have a nearly full scale signal on my Ham HT, old TH-G71A dual band, set to receive on GMRS/FRS channel 7. NO other radio I have shows anything there when set for the same channel/frequency.

https://en.wikipedia.org/wiki/Image_response

https://www.electronics-notes.com/articles/radio/superheterodyne-receiver/image.php

[gortex2]

Do you have a different radio you can try to listen on to and see if it does the same ? Its not digital DMR or anything. To me seems like a carrier on the air maybe from a poor designed repeater or mobile someplace ? I'd be curious what a mobile or different radio would here ? 

[labreja]

Have you tried moving around your house or taking it outside and moving around to see if the signal strength changes or goes away?

 

[WRKG311]

The Houston area flood control uses frequencies just below GRMS for water depth guage for telemetry. Some are very dirty on the TX and bleed in. And the sound is much like what you are hearing. 

[WRQC527]

In my experience, some of the hash I hear on my radios is due to poor receiver filtering. I have a Wouxun HT and a QYT KT-8900 mobile that are unusable in the car, but other radios, like my Baofengs, worked fine. Something with the wheel speed sensors as far as I can tell because it only happens when I'm moving. My Yaesu FTM7250 mobile works fine until an Orange County Transit bus pulls up and overloads the receiver with some kind of RF. 

[Blaise]

OK, let's see:

I've checked it on my monitor Baofeng, a Motorola Talkabout, and the Radioddity DB-20G mobile unit in my car. 

I pick it up around my house and in various places in my town.

I've compared the frequencies to local repeaters, and only one in the MyGMRS DB corresponds to either frequency.  The one that *dooes* correspond has been around forever and is actively maintained (and identifies itself when the static is gone, etc...)

It's hard to know if it's always the same thing, since I'm never running two radios at once, and I haven't done a systematized survey, but they*seem* to be a real transmissions...

[Sab02r]

On 1/19/2023 at 2:26 PM, WRQC527 said:

In my experience, some of the hash I hear on my radios is due to poor receiver filtering. I have a Wouxun HT and a QYT KT-8900 mobile that are unusable in the car, but other radios, like my Baofengs, worked fine. Something with the wheel speed sensors as far as I can tell because it only happens when I'm moving. My Yaesu FTM7250 mobile works fine until an Orange County Transit bus pulls up and overloads the receiver with some kind of RF. 

Perhaps it is the tire pressure monitoring sensors.

"TPMS sensors operate at one of two frequencies, 315MHz, and 433MHz. The frequency of the sensor used is determined by the vehicle manufacturer. "

"In rolling mode, sensors transmit, on average, once every 30-120 seconds. While parked or in stationary mode, depending on the manufacturer, sensors may transmit only when a significant pressure change is detected. If a TPMS sensor transmitted all the time, a sensor would not last very long." - Stolen from Google

[Sab02r]

The source of the signal is clearly aliens. The signal is a countdown which will end on "Independence Day" 

Are there any large manufacturers or pipeline pump stations nearby?  Light rail or hydro-power perhaps?

What is your squelch set to?  What happens if you try to communicate on a frequency exhibiting the noise from your HT to your mobile, or vice-versa?

[WRQC527]

10 minutes ago, Sab02r said:

Perhaps it is the tire pressure monitoring sensors.

My van doesn't have tire pressure monitors. It uses the ABS wheel sensors to monitor the rotating speed of each tire. If a wheel is rotating faster than  the rest, as it would be when the tire has lower pressure and therefore a smaller diameter than the others, it triggers the low tire pressure warning light. Very effective system. And it only works when the van is moving. Another possibility is the vehicle speed sensor or its associated electronics. 

[Sab02r]

In my experience, wheel-speed sensors and vehicle speed sensors are hard-wired components instead of radio...but my experience clearly doesn't extend to your van so I have no doubt that you are correct.

[WRUH396]

People are covering some a lot of good info above.  As one that spends a lot of time on VHF/UFH I can tell you there are some really pesky interference sources lately.  The extra wide or drifting carrier is kind of a telltale sign it is not likely a radio.  The most common we have tracked down recently are: 

Switching Power Supplies 
Cell and USB chargers Home and Auto (They switching powers supplies) - this is very common in cars and comes and goes as the device charges
Solar Chargers and Grid-Tie Inverters - people are adding more and more solar arrays by the day. (Worse during daylight hours) 
LED lighting systems

If it really gets annoying buy or borrow a cheap SDR donglem go mobile and use that with a portable laptop to track it down.  Also check your own house as well.  I will see if I can find a spectrum pic of some of the madness we have seen.   

[WRUH396]

This is the kind of stuff we see.  This one is actually on HF but we have seen this noise much higher into VHF/UHF as well but this type of unnatural spikes across the band or covering multiple channel slots is what you want to find.  Look at the visible jagged spikes below.   

The other thing to keep in mind, though not as likely as you mentioned you tried a few different radios, but as 935 was pointing out on my post that a lot of this SOC/SDR style, cheap Chinese radios have the front-ends as wide as a barn door and are susceptible to desensing, mixing and intermod.  There is an area near where I live by the airport and county dispatch that any Baufeng, BTECH or other cheap SDR gets slammed and sometimes it is so clear it sounds like they are dispatching right on GMRS or our UHF frequency but we don't get that at all on Yaesu, Kenwood or Icoms. 

[WRQC527]

2 hours ago, Sab02r said:

In my experience, wheel-speed sensors and vehicle speed sensors are hard-wired

Yes, the sensors are hard-wired but they are triggered by electrical pulses generated by a Hall-effect slotted ring on the wheel hubs. My guess is that these electrical pulses break the squelch on the radios, which is very annoying. It doesn't happen on all my radios, and not in all my vehicles. 

[MarkInTampa]

14 hours ago, WRUH396 said:

This is the kind of stuff we see.  This one is actually on HF but we have seen this noise much higher into VHF/UHF as well but this type of unnatural spikes across the band or covering multiple channel slots is what you want to find.  Look at the visible jagged spikes below.   

The other thing to keep in mind, though not as likely as you mentioned you tried a few different radios, but as 935 was pointing out on my post that a lot of this SOC/SDR style, cheap Chinese radios have the front-ends as wide as a barn door and are susceptible to desensing, mixing and intermod.  There is an area near where I live by the airport and county dispatch that any Baufeng, BTECH or other cheap SDR gets slammed and sometimes it is so clear it sounds like they are dispatching right on GMRS or our UHF frequency but we don't get that at all on Yaesu, Kenwood or Icoms. 

I get a lot of spikes (and interference) on UHF that is caused by a mistuned or cheap antenna. See example below taken this morning about 1 minute apart (time it took to swap coax). I also have someone around here running DMR simplex on 462.700 that hardly breaks the squelch and almost sounds like static not DMR on a HT and causes slight interference with the area .700 repeater (fixed the squelch issue by enabling CTCSS on receive) but I can still use it. On my base station the DMR comes through almost full power and makes the repeater useless because of how strong the signal is. 

Good antenna

Cheaper antenna

[Lscott]

Unless I'm miss reading the waterfall display the frequency is 442.775 MHz which is in the Ham 70cm band. That's not GMRS.

[MarkInTampa]

1 minute ago, Lscott said:

Unless I'm miss reading the waterfall display the frequency is 442.775 MHz which is in the Ham 70cm band. That's not GMRS.

Your reading it right, tested in the early morning and there was no activity at the time on 462.xxx. There was on 442

[WRPK937]

Similar occurrence in my area. .675 is 24/7 static.

I get it both radios Mobile and HT. Squelch setting has no impact on it, at any setting 0 to 9.

I just reprogrammed the squelch setting levels on my Baofeng via Chirp. Unfortunately, Chirp does not yet recognize my MXT500. Hoping the new levels will allow the Baofeng to scan past channel 20 now, if not back to scan skip. I followed this article for new squelch levels.  UV5R/UV82 Squelch Levels - Miklor

I've programmed channel 20 to scan skip on both my Midland MXT500 mobile and my Baofeng GMRS-9.