Mounting GMRS antenna

[jsalbre]

Here is the NMO trunk lip mount on the hood. I have one on each side although I haven' t run the cables yet. The Larsen dual band 2m/70cm antenna coil pictured is a little larger diameter than the mount and looks a little funny.

The whole point here is the hood is about the only place on the vehicle to get an adequate ground plane for an antenna. Sticking them out the side or up high above any flat sheet metal will seriously reduce the performance and range plus some antennas will never match up right, especially CB antennas.

I've also covered the underside of the plastic cowl parts behind the antenna with a wide aluminum tape that bonds to the vehicle sheet metal below it to extend the ground plane.

That makes more sense now, thanks! And the hood opens with no issues, aside from having to remove the aerial I assume?

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[Radio Guy]

Hood opens fine, plenty of room in the gap for the mount and coax to clear and when the hood is open the antenna lays back and doesn't touch the windshield with the hood prop in. The hood will open further and at that point you would want to remove any antennas.

That makes more sense now, thanks! And the hood opens with no issues, aside from having to remove the aerial I assume?

 

[Radio Guy]

I'll add add more info here to my antenna install that's only in the beginning phase. I found a good place to run coax for the driver side hood lip mount. The first picture shows some white 14ga house wire I used as a fish line into an existing fire wall hole on the drivers side that had a grommet and you have to look carefully in the pic for the wire. The exit point inside the cab is under the plastic trim piece in the door jamb and you can see the wire sticking out in the third picture.

To get the wire through you have to visualize the space in 3D and push the wire slightly upward and towards the door to hit the right path, then grab the wire with needle noise pliers. Most of my radios will go under the back seat so there is an easy path under the plastic trim downward and back.

Before taping the coax to the fish wire and pulling through I cut a slot in the rubber grommet and fed that over the coax so when the coax is in you can slide the grommet into place and snap back in.

 

[Frogwopp]

I'll add add more info here to my antenna install that's only in the beginning phase. I found a good place to run coax for the driver side hood lip mount. The first picture shows some white 14ga house wire I used as a fish line into an existing fire wall hole on the drivers side that had a grommet and you have to look carefully in the pic for the wire. The exit point inside the cab is under the plastic trim piece in the door jamb and you can see the wire sticking out in the third picture.

To get the wire through you have to visualize the space in 3D and push the wire slightly upward and towards the door to hit the right path, then grab the wire with needle noise pliers. Most of my radios will go under the back seat so there is an easy path under the plastic trim downward and back.

Before taping the coax to the fish wire and pulling through I cut a slot in the rubber grommet and fed that over the coax so when the coax is in you can slide the grommet into place and snap back in.

Another option for going through the firewall is that round plug above the hole you passed through. It has 2 tabs you grab and give a quarter twist to remove. I drilled a hole through center of that, passed my antenna cable and reinstalled. You can see the hole from drivers footwell, no fishing wire needed.

 

[Radio Guy]

Thanks, I'll save that for the next drivers side project. I have some 4ga power wiring and another antenna on the passenger side and I need to find a firewall pass through for those. Doesn't look like much fun with the battery and fuse box in the way.

Another option for going through the firewall is that round plug above the hole you passed through. It has 2 tabs you grab and give a quarter twist to remove. I drilled a hole through center of that, passed my antenna cable and reinstalled. You can see the hole from drivers footwell, no fishing wire needed.

 

[sarguy1941]

PRC if your going to the back of the seats with power you can follow the frame rail ad go thru a plug under the back seat on the passengers side(well just before). You can see the plug just in front of the box under the seat. I ran a #4 from the battery in loom then up and thru for my 8500 and FTM. Its probably overkill but I always run for the future. I ran my 1 NMO antenna on the back rack thru that grommet also.

 

[Radio Guy]

Is that route externa of the cab? I usually poke through the firewall then starting under the dash I run the wiring in the cable troughs that run past each lower door opening. I just need to find a firewall plug or grommet on the passenger side. Tell me more about your frame rail run and how you got the wiring from the battery into the frame rail.

PRC if your going to the back of the seats with power you can follow the frame rail ad go thru a plug under the back seat on the passengers side(well just before). You can see the plug just in front of the box under the seat. I ran a #4 from the battery in loom then up and thru for my 8500 and FTM. Its probably overkill but I always run for the future. I ran my 1 NMO antenna on the back rack thru that grommet also.

 

[Radio Guy]

Another thing I do on some antenna installs with questionable ground plane is add some ferrite to the coax to choke off common mode RF currents that might be riding on the coax shield. This install using the entire hood as a ground plane doesn't really need it for 2m or 70cm amateur bands but I might stick a CB antenna on one of these mounts and the hood is technically not large enough for a good ground plane at CB frequencies.

What can happen when the ground plane is too small is the coax tries to become part of the antenna system and it can become hot with RF and radiate. Much of the wiring in the vehicle cab is run in metal troughs and not that susceptible to RF interference but when you bring an RF hot piece of coax running in the trough parallel with sensor and other wires it can cause problems. You can also pick up RFI onto the shield of the coax from the vehicle wiring and it can ride up the shield to the antenna where its received.

In this case I used what I had, a ferrite mix that favors the VHF/UHF bands with the four snap on beads giving a good 1200 ohms choking impedance on 2m amateur, 1800 ohms on 70cm amateur and maybe 400 ohms for CB frequencies, which is not great but will absorb some RF on the shield. There are better ferrite mixes for CB and HF frequencies and with a different shape core you can wrap multiple turns through a ferrite core were each time you double the number of turns you get 4X the choking impedance.

The picture shows four snap on beads right below one of my hood lip NMO antenna mounts.

 

[sarguy1941]

Sorry been on road for work....anyway I put my cable in good split loom and followed the factory wire harness that's clipped to the frame rail. It drops down just behind the front tire (between inner and outer fender). I used the factory harness to fasten mine to. I don't rock crawl my JT but i do frequent off road and do check stuff. Other than some red clay I've seen no issues with the route.

I did dig around under the hood and some guys found a grommet under the batteries. Being there isn't a lot of room along the step area/side of the tub anyway I thought this was the best. I have my 8500 and FTM control cables run there so it got power away from those.

I can try to snap a picture or two tomorrow if its not raining.

 

[Radio Guy]

Sorry been on road for work....anyway I put my cable in good split loom and followed the factory wire harness that's clipped to the frame rail. It drops down just behind the front tire (between inner and outer fender). I used the factory harness to fasten mine to. I don't rock crawl my JT but i do frequent off road and do check stuff. Other than some red clay I've seen no issues with the route.

I did dig around under the hood and some guys found a grommet under the batteries. Being there isn't a lot of room along the step area/side of the tub anyway I thought this was the best. I have my 8500 and FTM control cables run there so it got power away from those.

I can try to snap a picture or two tomorrow if its not raining.

A pic would be great, thanks. I looked over the route you mention and I do see a clean path from the edge of the main battery down under the vehicle then I see parts of the frame are hollow with lots of large holes that could safely pass wires all the way to the rear seat area. Problem is I have an existing cable from my prior vehicle that would easily reach under the rear passenger seat by passing through the firewall and running inside the cab along the floor near the doors. Going outside to the frame eats up just enough length where my existing cables may not work. If there is a firewall grommet behind the battery/fuse box area I will dig around and try to find that before buying all new 4ga wiring.

 

[sarguy1941]

Here are 2 good posts with pics for passenger side stuff.

https://www.jeepgladiatorforum.com/...rough-grommet-in-firewall-any-pointers.25933/

https://www.jlwranglerforums.com/fo...-grommet-to-get-wires-through-firewall.41004/

The second is on a 2019 JL but has better pictures. You basically need to remove both batteries to get to the location. I dug around at one point inside and never could find the location so went to the frame rail. I was lucky as I had a new spool of wire and loom.

 

[Radio Guy]

I looked things over today and didn't want to spend a lot of time taking out both batteries to find my model doesn't have a passenger side feed through, so I ordered 20ft of red and black 4ga with some big crimp lugs and will go the frame route. I have a spool of expanding web loom and will cover the wires with that over the entire run. I need the big wire to occasionally power an SGC 500W HF amp.

 

[rharr]

Hey guys, how are you powering your radio? Straight off the battery or using the cigarette lighter plug?

If I don't connect it to the battery, not sure where to connect, I don't want to connect it to the cigarette lighter in the dash and have a cord cluttering things up. Anyone run a power wire into the center console and put a lighter plug in there?

I am thinking of installing the radio under the driver seat hence the center console power tap but I am open for other ideas.

going to do a stubby antenna and use a hood clip like others here.

 

[smlobx]

I connect mine by using one of the auxiliary switches. Works great.

 

[Jay Gatsby]

^^^ What smlobx said. Wired my ham radio direct, but for the GMRS Aux is good enough.

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