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Signal Noise Identification

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#1
Hi all.

Can anyone identify what this signal noise represents?

@154425000Hz NFM

https://www.dropbox.com/s/amcj2gjevh687zf/Signal Noise Identification.mp3?dl=0

The second audio clip is scratching/clicking noise between analog police 2-way transmissions. It's very loud and annoying when listening via speakers.
However, what I've just noticed is that the noise almost dissapears when listening via earphones!
Any explanation as to why?

https://www.dropbox.com/s/lauv9ph4h6pnbrk/Noise Identification.mp3?dl=0


Mnny thanks
 
Joined
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#2
Hi all.

Can anyone identify what this signal noise represents?

@154425000Hz NFM

https://www.dropbox.com/s/amcj2gjevh687zf/Signal Noise Identification.mp3?dl=0

The second audio clip is scratching/clicking noise between analog police 2-way transmissions. It's very loud and annoying when listening via speakers.
However, what I've just noticed is that the noise almost dissapears when listening via earphones!
Any explanation as to why?

https://www.dropbox.com/s/lauv9ph4h6pnbrk/Noise Identification.mp3?dl=0


Mnny thanks
The first one sounds very much like a Motorola 3600 baud Smartnet control channel. I would not expect it to be on a VHF frequency let alone 154.425 MHz that doesn't seem to be a valid FCC allocation. Are you in the US or Canada? Can you determine who the licensee is?

The second one? Tighten your squelch control....
 

dpcain

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#3
The first is DMR... and your noted frequency may be off (quite likely if you're using an SDR). RFI-EMI is right on the money, that's an invalid FCC alloc for the US if you're here.

Same as he said for the second one too. Your squelch is at a low threshold and your radio is unsquelching for little chunks of basic, useless noise that pop above your squelch threshold.
 
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Gilcrest, CO
#4
The second audio clip is scratching/clicking noise between analog police 2-way transmissions. It's very loud and annoying when listening via speakers.
However, what I've just noticed is that the noise almost dissapears when listening via earphones!
Any explanation as to why?
If the speakers are plugged into the wall or a cigarette lighter for power the extra grounding provided by the wall adapter or cigarette lighter adapter are likely the culprit of the extra noise. It could be noise in the power grid or vehicle entering the scanner via the power connection.

Shawn
 
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Messages
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#9
The first one sounds very much like a Motorola 3600 baud Smartnet control channel. I would not expect it to be on a VHF frequency let alone 154.425 MHz that doesn't seem to be a valid FCC allocation. Are you in the US or Canada? Can you determine who the licensee is?

The second one? Tighten your squelch control....
Hi RFI-EMI-GUY.

Many thanks for your reply!

Firstly, just wanted to mention that I am a total newbie to scanning, barely a month now! :)
Secondly, I forgot to mention that I am using RTL SDR, with the stock whip antenna, indoors. And SDR# software,

Now, to your questions:

I am not form North America! So don't panic! lol

In my location, I pick up police analog communication between 154-156ish MHz.

Is the "Motorola 3600 baud Smartnet control channel" used for digital police/emergency communication?
If so, it would make sense that it's broadcasting at this frequency, given the frequency range I pick up police radio, no?

How do I determine the licensee?

Lastly, how do you "tighten squelsh control" in SDR#?

Thanks
 
Joined
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Messages
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Location
Lockport, IL
#10
Yep, that's DMR.

In SDR Sharp, the Radio section, along with the mode and step size and so on is a squelch value. Set it larger to raise the threshold.

Those RTL dongles are notorious for being off frequency. In the device settings (the 'gear' icon between the 'play' and speaker) there is a frequency correction in ppm. You can adjust here to improve accuracy. Around +80 seems to be good but it will vary for whatever model you have. It also moves a bit as the device temperature changes. And for some reason alternate drivers do not center with the same value. Find a known signal, something always on that you believe to be accurate. The IF spectrum display can help you with this. Adjust the offset until you find the carrier dead center. You can use the FM broadcast band stations but you can only see the carrier during silence. If there's weather stations where you live they can be used. Set it in VHF and then look at it in UHF. You will likely find it's off a little in one or the other but it should be pretty close. Then you'll know when you find something what the true frequency is. And yes, sometimes things are actually off frequency.
 
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