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grounding a larsen nmo150/450/800 ?????

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hello i got a larsen nmo 150/450/800 mhz antenna with a mag mount. and im picking up alot of what seems to be tv shows i turn my squelch up almost all the way before the interference stops. pluss im not picking up like i thank i should be i mean it does good but some times i can pick up static and then i put my factory antenna on it while its picking up static and i can here it fine and then other times it comes in a little better than the factory antenna i just bought this antenna and was just wondering if it was defective and then some one told me im loosing alot buy not having it grounded. im useing a mag mount with 12 feet of coax with a screw on bnc to hook up to my pro 164. i use it in the car and when im not riding i take it out and use it in the house. so what am i doing wrong? and what do i need to improve this to make it better? do i need to have it grounded.?
 

n9mxq

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#2
Nobody else has said it, so I will....


Drill the hole.. It's your best solution, and the best way to give the antenna the ground plane it needs. Magnet mounts don't ground to the metal that well. Heck most have plastic over the magnets..

Do a forum search for NMO and drill, you'll find several threads on it.. And if you google the same, I'm sure there's step by step instructions out there too..
 

ka3jjz

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#4
lugoff, you're clearly experiencing intermod - basically your scanner is being overloaded by TV signals that are generating false signals in various parts of the spectrum.

Do you have a TV or FM station that's very close to you? I know the PRO97 has a reputation of being very sensitive to overloading issues in the VHF hi band (140-170 mhz area). Is this where you're having the problem?

The scanners are not defective per se - consumer grade scanners have issues like these due to cost-cutting and poor design.

73 Mike
 
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#5
I have the same mag mount and a PRO-97 and was in Needham, right in the near field of all the Boston TV and radio station towers and get no interference whatsoever. A well constructed mag mount inductively couples to the body of the vehicle. The plastic is actually polypropylene which is used so that the magnet does not mar the finish. I would not blame the antenna, Larsen doesn't make a lousy antenna, I only buy Larsen.
 
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#6
Cable TV uses several vhf/uhf frequencies to transmit tv signals through thier cable systems. Some of these are in the ham/public safety bands. If there is a leak in the cable system or someone hasnt properly terminated an unused cable connection you will get this type of interference and there dosent have to be anything wrong with the antenna or scanner. Most cable companies are very helpful in finding these leaks...
 
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#7
Try using a different antenna, not saying anything is wrong with the one you have.
Just try another one and see if the condition's get any better.
 
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#8
Paulsan said:
What is a screw on BNC? Do you mean on the end of the coax?
well what i got is a mag mound and at the end of the coax i can screw it in a base type scanner rether than a portable so i bought a bnc connector and screw it on to it to make it work for the pro 164 what im really needing to know is do i got to ground it and if so were do i put my ground at on the antenna and what size of ground cable do i need
 
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#10
Oh, ok. I wasn't sure what it was. Thanks.

I've heard that putting a mobile antenna on a pizza pan will help when using it as a base antenna. I never tried it and have no idea if it's true. Others here are more qualified to answer your question about interference. Good luck.
 
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#11
lugoffman said:
hello i got a larsen nmo 150/450/800 mhz antenna with a mag mount. and im picking up alot of what seems to be tv shows i turn my squelch up almost all the way before the interference stops. pluss im not picking up like i thank i should be i mean it does good but some times i can pick up static and then i put my factory antenna on it while its picking up static and i can here it fine and then other times it comes in a little better than the factory antenna i just bought this antenna and was just wondering if it was defective and then some one told me im loosing alot buy not having it grounded. im useing a mag mount with 12 feet of coax with a screw on bnc to hook up to my pro 164. i use it in the car and when im not riding i take it out and use it in the house. so what am i doing wrong? and what do i need to improve this to make it better? do i need to have it grounded.?
so were do i put my ground at on the antenna and what size of ground cable do i need
 
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#12
There will be no perceivable difference using the Larsen Tri-band with a mag mount compared to a permanent mount in the same location on a vehicle. VHF low band and HF will have some difference but not VHF hi and up.
prcguy
lugoffman said:
so were do i put my ground at on the antenna and what size of ground cable do i need
 
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#13
You don't need a ground. The mag mount inductively couples with the surface it is attached to, creating a ground or ground plane, depending on how much surface is under it.

When you say a screw on BNC, you must mean you are using a BNC adapter.
 
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#14
N1BHH said:
You don't need a ground. The mag mount inductively couples with the surface it is attached to, creating a ground or ground plane, depending on how much surface is under it.

When you say a screw on BNC, you must mean you are using a BNC adapter.
yea im using a bnc adapter thats what i meant but it screws on to the end of the adapter from the coax i wanted to get that new redesined nmo mag mount that cheapham.com gots and try that
 
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#15
N1BHH said:
You don't need a ground. The mag mount inductively couples with the surface it is attached to, creating a ground or ground plane, depending on how much surface is under it.

When you say a screw on BNC, you must mean you are using a BNC adapter.
It wouldn't be a bad idea to take a multi-tester to the base and vehicle just to see if it really is well grounded or not. I just measured 5 ohms of resistance between my mag mount and car body. I'm in the process of trying to bond everything I can to the body of the car to cut down on the RFI I'm experiencing when listening to air bands.
 
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#16
K4DHR said:
It wouldn't be a bad idea to take a multi-tester to the base and vehicle just to see if it really is well grounded or not. I just measured 5 ohms of resistance between my mag mount and car body. I'm in the process of trying to bond everything I can to the body of the car to cut down on the RFI I'm experiencing when listening to air bands.
yea its a adapter i wish i had a pic to put on here so u can see it but i dont. i really know nothing about antennas and i was reading up on it but really i cant understand nothing some of it i can but some of it i cant im not sure what its refering to somtimes when i read it besacue of all the abbrevations they use . i dont know what they mean
 
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