What kind of noise is this?

[brandon]

Lately I've been getting this strange pulsing sound when monitoring 800 MHz systems. I scanned the entire 800 MHz range to find a possible source and I found a strong data signal on 854.550 that seems to be the culprit. The noise matches up with the interference on the public safety channels. It occasionally produces long burst of data that REALLY wipes out the band.

Here is a recording of the noise source on 854.550 - Link to audio

And here is a recording of how the interference sounds on a legit public safety freq - Link to audio

Does anyone know what kind of noise/interference this is. I assume it's some sort of Nextel or cellular interference and it's wrecking much of the 800 MHz public safety band. I notice it while monitoring Orange County, CA - a system that comes in at full bars... mostly happening on 858-860 range freqs. I do not get this problem when monitoring our local EDACS system but it uses freqs in the 866-868 range.

Would it be worth the time and effort to complain to the cellular company.... I doubt they would give a hoot. I think I am going to order a notch filter to cure the problem but I worry about this frequency changing if its part of some trunked cellular system.

 

[SouthSoundScanner]

In my old house, I would get a noise like that when the Furnace was on.

 

[DaveH]

It does sound like it could be iDEN (Nextel). The pulsating sound is
something fairly recent, within the last few years. Some scanners
seem to stop on iDEN signals which sound like a continuous dull
droning...like an airplane flying over the ocean.

Dave

 

[mancow]

It sounds like IF from a scanning receiver that stopped on a transmission for a while.

 

[SCPD]

It sounds like IF from a scanning receiver that stopped on a transmission for a while.

Yeah. If the actual users of the system aren't complaining ... the interference may be local to you. Nextel does care ... it costs them money every time the FCC hits them with an NAL.

-rick

 

[etofsrud]

It sounds like local IF to me also. A clock chip counting away. Start local and work out. Any adjacent scanners in the same room? How does it compare between external antenna and rubber antenna?

Eric N6OIM

 

[brandon]

Hello...

I did more testing and found when using the rubber duckie the interference does not occur - only happens when using the outdoor antenna. I also turned all the radios off and it happens so I don't think its the local IF.
I am going to have to get a filter because the ATT doesn't really help. Just hoping this frequency does not change on me if I go that route. Do cellular/Nextel systems use control channels that change freqs from time to time? I am not really familiar with those types of systems.

 

[etofsrud]

Interesting. You would think if it was radiating that strong, it would get other agencies attention. If you end up DF'ing it, let us know what you find. I've DF's some pretty weird stuff over the years. Most were week signals messing up our repeater input. Some TV antenna amplifiers, mast and attic. Florescent bank sigh transformers. And my favorite, the 144Mhz buzzing power poles. One good whack at the base with a 20 lbs sledge usually knocks the oxide off and the emissions stop. But these are all old school RFI cases. Yours seems to be CPU controlled. Good luck with it.

- Eric N6OIM

 

[NeFire242]

You don't hear it when you drive around the neighborhood then?

The cell company probably wouldn't care about you since it's just you and a scanner, now if the agency was complaining and had evidence supporting their claim that would be a case.

 

[kb2vxa]

Hi all,

About all I can say is by the sound and the looks of the waveform it seems to be timing (clock) pulses. I suspect the 854.55 recording is the same except has a high speed data signal in the middle that may or may not be related.

Now here's what really grabbed my attention.

"And my favorite, the 144Mhz buzzing power poles. One good whack at the base with a 20 lbs sledge usually knocks the oxide off and the emissions stop."

The emissions may or may not stop, you have no way of knowing when you're dead. When the sky lights up and you hear the devil's own noise overhead you don't have time to run, it could be you knocked of just a bit more than some oxide.

 

[DaveH]

I found an 850MHz frequency with a sound very similar to the one
posted here. I looked it up in the (Industry Canada) database and it's
an iDEN frequency. As for not getting the problem in the 868-869MHz
range, if the U.S. and Canada are the same, iDEN isn't in that sub-band
(rebanding notwithstanding...)(how's that for a political word).

Dave

 

[brandon]

Thx for the input. The noise seems to be in my local area. I do live pretty close to some cell sites - I would say between 1/4 to 1/2 mile away. I doubt the interference is causing problems to Orange County. I found it only happens on 2 frequencies out of the 20 or so on their main TRS site, so it's not the end of the world --- but does enough to annoy me.

One thing I noticed is when the burst of data occurs on 854.550 it causes 860.2125 (an Orange County TRS frequency) to be wiped out. Pretty nasty considering the Orange County system comes in with full bars on my scanner.

I tried the ATT and it doesn't really help so it's looking more like a notch filter is to be ordered. I am just going to wait a bit to make sure this frequency does not change on me. I would hate to order a custom filter and have it be useless because the freq changed a few MHz.

 

[brandon]

Just an update I drove around and believe I found the site causing the noise. It's one of those palm tree cell towers with some coconut looking box under the "palm leaves". I had a PRO-96 with me and as I got closer to the site the noise kept getting worse and worse until I could not hear any legit 800 MHz signal as I passed on the road next to the transmitter. The tower is probably less than 1500 ft from my antennas at home.

When I got home I hooked up my Icom PCR-1000 to get a better signal reading and the s-meter on 854.550 is fully maxing out at +55 to +60 over S9.

For what its worth I also found a couple other strong freqs close to that reading on the meter on 852.550 and 862.550 but they don't make that ticking noise instead just sound like an open squelch.

Bring on the re-branding. I can't wait!