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Author Topic: What causes the squelch to open on 2 meters?  (Read 648 times)
N8DV
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Posts: 59




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« on: June 18, 2008, 08:28:43 AM »

As I drive around town monitoring one of my favorite repeaters, 147.180 I will be driving and the squelch will open with silence and then I go a little farther and it stops. Is this a wireless connection that I am picking up or it is cable/dsl leakage? I am just curious why the squelch opens from time to time, not constantly just randomly as I approach private homes, and some businesses. Just curious. Thanks
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WA7NCL
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Posts: 625




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« Reply #1 on: June 18, 2008, 08:32:39 AM »

On an FM RX any signal that quiets the RX will open the squelch (assuming it is noise based).  Most likely it is cable system leakage and other RFI sources that make a carrier that quiets the RX.  I find the same thing in urban areas.  If your repeater is strong, just set the squelch level higher so that fewer RFI signals break the squelch.  Most RFI signals are not as strong as intential signals (at least lets hope so).
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W3ML
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Posts: 164




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« Reply #2 on: June 18, 2008, 08:35:10 AM »

In our little town we have two spots that do this. One is the hospital and the other is the tanning business.

Just set your squelch higher or drive on by it like we do.

John
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K0OD
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Posts: 2458




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« Reply #3 on: June 18, 2008, 09:15:48 AM »

"One is the hospital and the other is the tanning business."

VERY interesting. What would a tanning business be broadcasting? Hmmm
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K5END
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Posts: 1309




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« Reply #4 on: June 18, 2008, 09:26:23 AM »

"What would a tanning business be broadcasting? Hmmm "



Are you suggesting wireless cameras?

It might be interesting to "see" what they are broadcasting...
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AC5UP
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Posts: 3781




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« Reply #5 on: June 18, 2008, 09:35:52 AM »

Some proximity detectors on automatic door openers will trip a radar detector, wouldn't surprise me if they could do the same on Two with the help of a little intermod...

( ? )
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Yo...   Vinnie...   Is Governor Christie too big to fail?                
K0OD
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Posts: 2458




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« Reply #6 on: June 18, 2008, 09:43:22 AM »

Yes, and some might be fronts for prostitution. Could be a security camera. Check it out. I KNOW we'd all like to hear what a tanning salon is broadcasting. LOL

How to go about this??? Maybe call the FCC to see if a transmitter is licensed to that location. I don't know.

Another question: do tanning beds give off a lot of RF?
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WW5AA
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Posts: 2088




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« Reply #7 on: June 18, 2008, 09:50:34 AM »

The in-house BPL systems will do this as will poor commercial repeater set-ups.

73 de Lindy
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W0FM
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Posts: 2042




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« Reply #8 on: June 18, 2008, 10:56:19 AM »

A few years ago, we were experiencing random on-frequency "hits" on one of our 900 MHz trunking system channels.  With direction finding techniques and many, many man hours, we found the culprit.  It was the RF security tag system at a department store exit two blocks away.  We called the manufacturer and they swore it couldn't be their equipment.  We pulled the plug on their equipment and the "hits" went away.  Two days later they had a tech on site changing out the equipment.  

No more problems.  You just never know.

73,
Terry, WØFM
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KB1LKR
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Posts: 1895




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« Reply #9 on: June 18, 2008, 11:23:56 AM »

If the store was using a 900MHz UHF RFID system (862-955 MHz) then random hits on a 900MHz trunking system could occur, particularly if the power output was excessive/outside of the part 15 limits.

13.56 MHz HF RFID systems on the other hand...
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KZ1X
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Posts: 3217




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« Reply #10 on: June 18, 2008, 12:16:12 PM »

The fix is to have the repeater transmit PL on COR.  Then, set your radios for RX PL, and voila! you have what the cops have had for decades.  

That's what we do here.  Bonus is that crossband repeating to repeaters is done on PL, not COR, so there's no turn-around lag time via the crossband.  Just superb.  Why doesn't everyone do this?  I really don't know.

Only catch?  

This doesn't work for Yaesu owners, whose rigs have very slow PL decode ability.  Icom, Kenwood, Alinco, etc., all do their PL decode in dedicated hardware.
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N6AJR
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Posts: 9793




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« Reply #11 on: June 18, 2008, 12:24:59 PM »

I often get "un-squelched" in my car or truck when going to a fast food place.  seems like there is something in there that causes a lot of RF hash, perhaps their little headsets??  any how not an unusual occourance.
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K4JJL
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Posts: 452




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« Reply #12 on: June 18, 2008, 01:46:15 PM »

I used to pick up a lot of cable TV leaks when driving around my neighborhood (from shoddy cable terminations).

Tanning beds definitely generate RF, but it's more in the 2.4 GHz range.  I remember this from a UV light generator I was trying to get WiFi to work near.  The -23dBm from the generator completely covered up the -65dBm output from the access point.  Needless to say, I asked my boss for a tinfoil hat and tinfoil pants as I worked around it.  We solved the problem with a Faraday cage around the UV source.

I've never had a cable leak drown out an intended signal, but it definitely is annoying when it breaks the squelch.
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K5END
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Posts: 1309




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« Reply #13 on: June 18, 2008, 02:28:17 PM »

We had interference on our licensed 928 MHz SCADA--only occured at night. It was a brief key up at about 1 second periods.

Turns out it was a varmint/electric fence with a leaf laying across it arc-ing to ground, and the subsequent EMI noise hitting nearby signal wiring and keying up one of our own RTU transmitters. It was only turned on at night to protect equipment from nocturnal critters.

The dreaded SPARK GAP transmitter, hi.

Point is, it wasn't even an RF device causing the problem. The interference was a true radio, but the problem  that was keying the radio wasn't.
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N4MJG
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Posts: 490


WWW

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« Reply #14 on: June 18, 2008, 02:34:55 PM »

Sound like RF to me,when i go to automatic door it made 2 meter go nuts,it can be anything causing the RF in business maybe automatic door got something do with. been there and done that !!

73
Jackie
KG4ORX
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