NMO mount problems

[chrish04]

I am having problems with my mount. It does not receive well with the antenna screwed on, but if I take the
Antenna off it gets a good strong signal from the closest tower. I have tested my coax cable with a meter and I know that the cable is not the problem. Do you think that the antenna is grounding out on the roof of my truck when I screw it on it the mount? I'm out of ideas Bc I got my old nmo mag mount out to test the antenna on it and it works perfect on the mag mount. So I've been stuck using the mag mount untill I can find the problem with my roof mount.


Thanks In advance
Chris

 

[jhooten]

What kind of antenna?

 

[nd5y]

I have a Comet dual band antenna that shorted out an NMO mount.
The bottom of the antenna is all brass except for a small area around the center pin.
The NMO mount center contact was larger in diamater and overlapped the insulated center part of the antenna and it also stuck up too high.
I had to file down the contact on the mount and take a dremel tool and grind down the brass around the antenna center pin to keep them from shorting together when the antenna was screwed onto the mount.

 

[chrish04]

What kind of antenna?

motorola 800mhz antenna - Product Details

That's the antenna I have now , but it was doing the same thing with the antenna I had on there for a year or so. It went from working one day to nothing the next day.

 

[chrish04]

I have a Comet dual band antenna that shorted out an NMO mount.
The bottom of the antenna is all brass except for a small area around the center pin.
The NMO mount center contact was larger in diamater and overlapped the insulated center part of the antenna and it also stuck up too high.
I had to file down the contact on the mount and take a dremel tool and grind down the brass around the antenna center pin to keep them from shorting together when the antenna was screwed onto the mount.

I took some pictures of the bottom of my antenna and of my mount , but it won't let me load them because I'm on my phone. Could you PM me your email so I could email them to you and let you take a look

 

[jhooten]

It sounds more like the shield of the coax is open. Take the antenna off and unplug from the radio. Check from the shell of the connector to the body of the vehicle and from the shell of the connector to the outer ring of the NMO.

 

[chrish04]

When your talking about the shell are you talking about the plastic piece that covers the the connection where the coax connect to the mount?

 

[jhooten]

the outer metal part of the connector that attaches to the radio.

 

[chrish04]

The shell does have a couple little metal wires coming out be where it was crimped

 

[WA0CBW]

Maybe you didn't know but.........

Not all NMO mounts are the same. Each manufacturer seems to vary the height, and diameter of the center pin. The center pin is larger in diameter for the higher frequencies (800 Mhz and up). Some manufacturers have a removable center pin that allows you to select low or high frequency. Others have two different mounts. When installing NMO mounts be sure to check that the height and diameter of the center pin matches the center pin contact in the antenna base.

BB

 

[chrish04]

I've tried everything you guys have suggested and still no luck, I guess I'll just have to keep using the mag mount but I hate having the coax showing, it just doesn't look professional. I called the Motorola dealer in my town and they won't even take a look at it because it's for a scanner

 

[Coonassbill]

I've tried everything you guys have suggested and still no luck, I guess I'll just have to keep using the mag mount but I hate having the coax showing, it just doesn't look professional. I called the Motorola dealer in my town and they won't even take a look at it because it's for a scanner

Make sure that the center contact actually makes contact with the antenna connection. I have seen many questionable installations that this is why the antenna failed to receive/transmit.

 

[Mtnrider]

Pictures would say 1000 words.....of the roof mount,antenna and the connector...

 

[LarrySC]

N9QO is correct. Commom problem is Center Pin on antenna does not touch center stud of mount. Put meter on antenna and Center pin of BNC connector. Must have contact all the way thru. Dual band Ham antenna not the best choice for scanner. Use MAXRAD or simular dual band 150/450 for hot receive. Good Luck.

 

[chrish04]

Pictures would say 1000 words.....of the roof mount,antenna and the connector...

I have pictures but I'm using my phone to post on here and it won't let me post them on here. I could email them to you

 

[chrish04]

N9QO is correct. Commom problem is Center Pin on antenna does not touch center stud of mount. Put meter on antenna and Center pin of BNC connector. Must have contact all the way thru. Dual band Ham antenna not the best choice for scanner. Use MAXRAD or simular dual band 150/450 for hot receive. Good Luck.

I'm not using a ham radio antenna I'm using a Motorola low profile 700-800mhz antenna

 

[jhooten]

He has the proper NMO mount for the antenna he is using.

Check your email. Skip down to the sentence that starts Wait a minute

 

[DARRELL34]

I am having problems with my mount. It does not receive well with the antenna screwed on, but if I take the
Antenna off it gets a good strong signal from the closest tower. I have tested my coax cable with a meter and I know that the cable is not the problem. Do you think that the antenna is grounding out on the roof of my truck when I screw it on it the mount? I'm out of ideas Bc I got my old nmo mag mount out to test the antenna on it and it works perfect on the mag mount. So I've been stuck using the mag mount untill I can find the problem with my roof mount.


Thanks In advance
Chris

it could be a ground or what is you ohm meter reading with and with out the ant on