Antenna Grounding

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btritch

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I have an antenna mounted on an aluminum tookbox in the truck bed, however the box is only held on the truck by clamps, The radio I'm using, a Kenwood 7160 won't pick up hardly anything at all, my theory is this is because the antenna is not getting ground from the toolbox, I'm wondering if it would improve if I actually bolted the box to the truck bed or somehow grounded the antenna itself. Anyone have any suggestions or advice ?
 

Wil-lee

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I have an antenna mounted on an aluminum tookbox in the truck bed, however the box is only held on the truck by clamps, The radio I'm using, a Kenwood 7160 won't pick up hardly anything at all, my theory is this is because the antenna is not getting ground from the toolbox, I'm wondering if it would improve if I actually bolted the box to the truck bed or somehow grounded the antenna itself. Anyone have any suggestions or advice ?

That depends on the antenna ... if it is a dual band 5/8 wave then it dont need much of a ground.
Mine is mounted on a plastic bed cover and it works just fine.
If it is a 1/4 wave whip then yes ... the ground could make a difference.
That the coax feeding the antenna has a ground path.
 

mmckenna

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VHF needs a ground plane ideally 19 inches in diameter for the 2 meter band. Slightly less for the commercial/public safety sections of the band.

You have a decent ground plane in the tool box. May not be perfect, depending on the size of the box, but you've got one.
Ground planes are really important for transmitting. While important for receiving, a less than ideal ground plane is not going to prevent you from hearing something.

I'd really suspect that you either have a bad connection somewhere, an issue with the base/coil/whip mounting, or a bad connection.

Mounting the antenna below the cab is going to create some issues, can you try mounting it on top of the cab?

You'd need to do some testing to figure out where the failure is. Without knowing your skill level or what sort of test tools you have, I can't tell you where to start. A multimeter would be a good way to test this, if you have access to one.

Good places to take a look for issues:
Make sure the antenna base is making contact with the antenna mount.
Make sure the contacts are free of corrosion.
Check the underside of the antenna mount. Make sure the cable isn't separated, corroded, damaged, shorted to the mount, etc.
Check all of the coaxial cable for breaks, cuts where water can get in, etc. Pay special attention to where the cable enters the vehicle.
Check the connector. Be wary of any adapters.
Try connecting a temporary antenna directly to the back of the radio and see if it works.
Make sure the frequency you are listening to hasn't been changed.
If you have a separate radio, try connecting that to the antenna.

Couple of questions...
What type of antenna?
What type of mount?
How is the coaxial cable routed to the radio? Specifically, how does it get into the cab?
Did the radio ever receive anything? Or is the issue something that happened spontaneously.
Probably a bunch of other questions, but we've got to start somewhere.
 

btritch

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VHF needs a ground plane ideally 19 inches in diameter for the 2 meter band. Slightly less for the commercial/public safety sections of the band.

You have a decent ground plane in the tool box. May not be perfect, depending on the size of the box, but you've got one.
Ground planes are really important for transmitting. While important for receiving, a less than ideal ground plane is not going to prevent you from hearing something.

I'd really suspect that you either have a bad connection somewhere, an issue with the base/coil/whip mounting, or a bad connection.

Mounting the antenna below the cab is going to create some issues, can you try mounting it on top of the cab?

You'd need to do some testing to figure out where the failure is. Without knowing your skill level or what sort of test tools you have, I can't tell you where to start. A multimeter would be a good way to test this, if you have access to one.

Good places to take a look for issues:
Make sure the antenna base is making contact with the antenna mount.
Make sure the contacts are free of corrosion.
Check the underside of the antenna mount. Make sure the cable isn't separated, corroded, damaged, shorted to the mount, etc.
Check all of the coaxial cable for breaks, cuts where water can get in, etc. Pay special attention to where the cable enters the vehicle.
Check the connector. Be wary of any adapters.
Try connecting a temporary antenna directly to the back of the radio and see if it works.
Make sure the frequency you are listening to hasn't been changed.
If you have a separate radio, try connecting that to the antenna.

Couple of questions...
What type of antenna?
What type of mount?
How is the coaxial cable routed to the radio? Specifically, how does it get into the cab?
Did the radio ever receive anything? Or is the issue something that happened spontaneously.
Probably a bunch of other questions, but we've got to start somewhere.

I'm not exactly sure what kind of antenna it is, it was ordered for public safety, it's a quarter wave I think, I can probably find out if need be. . It's an NMO mount mounted into a drilled hole on the box, it's ran in the cab through an air vent on the back of the cab behind the seat, it picks up some channels but there are a couple it won't pick up for nothing, a handheld will pick them up better, I know they're the same frequency though, that's why I was leaning toward ground. I'll check for issues though elsewhere as well, I know we were in a town about 26 miles away today and it never picked up a thing that a pager heard perfectly. It's just weird.
 

krokus

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I'm not exactly sure what kind of antenna it is, it was ordered for public safety, it's a quarter wave I think, I can probably find out if need be. . It's an NMO mount mounted into a drilled hole on the box, it's ran in the cab through an air vent on the back of the cab behind the seat, it picks up some channels but there are a couple it won't pick up for nothing, a handheld will pick them up better, I know they're the same frequency though, that's why I was leaning toward ground. I'll check for issues though elsewhere as well, I know we were in a town about 26 miles away today and it never picked up a thing that a pager heard perfectly. It's just weird.
That makes me wonder if the antenna is for the correct frequency range. (On top of the other issues that have been mentioned.)

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btritch

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That makes me wonder if the antenna is for the correct frequency range. (On top of the other issues that have been mentioned.)

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It's a friend's antenna, I have an NMO mount as well, I'll pull mine off and screw it onto his base and see what that does, that will eliminate one possibly.
 

mmckenna

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Mounting the antenna on the tool box behind the cab is going to create quite a few issues. Putting it below the cab is going to basically put it in the shadow. The ground plane is likely a bit less than ideal, but not likely to be the cause. Cable routing can be an issue, make sure it's not damaged.

Making sure you have the correct antenna for the band you are using is important. For VHF frequencies, your 1/4 wave antenna will be about 18 inches tall. For UHF, about 6 inches tall. For 700-800MHz, about 3 inches tall. You'd really want to put that on top of the cab.

If you are using low band, then 1/4 wave can be anywhere from 110 to 54 inches tall, depending on the frequency.

If it was installed by a professional/radio shop, go back and have them check it out. If you did the install, you'll have to do some trouble shooting to figure this out.
 
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