Mounting GMRS antenna

[MikekiM]

Exploring options for comms.

I have a Midland CB that I have yet to install. It was previously in one of my JKs and my memory of it was that setup was extremely finicky. Never really got it to operate at it’s max.

Deciding whether it makes sense to switch to Midland MXT275 GMRS which seems to be plug and play.

Two questions…

Can the cable for GMRS be routed in the same bundle as 12v power or will that create static/interference? I have a bundle of aux wires running along the passenger side rocker above the jack tools and that would be the perfect route for the rear mounted antenna.

The preferred mounting location for the antenna would be on the upper arm of the Bestop HighRock Oversize Carrier. Possibly using a billet aluminum mount like this…

All points where the tire carrier mounts to the tub are insulated with rubber pads, effectively eliminating any grounding of the carrier components. Does a GMRS antenna rely on ground plane and if so could I wrap the coax for the antenna with a braided ground wire run back to the tub?

I’d like to have the mount such that I can switch between the standard antenna (if possible), the 3db Ghost antenna and a 6db whip.

An alternative would be to use the Midland Rollbar/Mirror mount in the same location or bumper/frame mount as pictured on the Midland site…

The latter would mean a much shorter run of antenna cable, eliminate the bundling with 12v wires and resolve the grounding concerns If there actually are any…

 

[Mr. Bills]

1. If CB isn't obsolete already, it soon will be. Unless you run with people who use CB, try GMRS instead.

2. You may or may not pick up interference from adjacent 12v wires running along side your antenna coax. If you do, you can shield your coax by running it through a length of tinned copper braid and grounding one end of the braid to a convenient bolt. This also works to shield radio power wires in the engine compartment from electrical noise.

3. Both CB antennas and GMRS antennas require a ground plane. Your antenna mount will need a good RF ground to the tub. Tinned copper braid works much better than wire.

Here is a source for copper braid ( I use 1/2" for ground straps, 3/4" or 1" for shielding coax and power wires: https://www.amazon.com/gp/product/B01BIBQ940/?tag=wranglerorg-20


PS - "Bonding" will help any radio installation, i.e., bonding the antenna mount to the tub, the tub to the frame, the tail pipe to the frame, hood to tub, etc.

A good article is here: http://www.k0bg.com/bonding.html

 

[MikekiM]

Thank you.

I’m aware of the fate of the CB. My primary use is going to be to communicate with folks on the outer beach within a few miles. No way to know what they might be using. I would be close enough to have a handheld GMRS at home for communication with family. I live on the water about two miles from the outer beach as the crow flies, so unobstructed line of sight across the bay, about two to three miles.

I have a grounding cable purchased when I thought I would be installing the CB. One of these…

Having a chance to put my thoughts to written word, I am liking the idea of mounting to the front bumper as pictured above. I can mount to one side or to the KC light mount on my front bumper which is all tied in to the frame. Plus there is a ground bolt on the passenger side frame rail I could connect to.

I can move the air coupler to the other side and use this spot inches away from the ground bolt.

Does that make sense?

 

[Zorba]

Running the coax next to the DC power lines will have exactly the square root of fuck all effect on the reception. No interference whatsoever.

 

[Mr. Bills]

I have a grounding cable purchased when I thought I would be installing the CB. One of these…
View attachment 439807

That should work for you now. You can also buy tinned copper braid and crimp on your own ring terminals rather than be limited to pre-made lengths.

While @Zorba may think that there can never be interference as a result of running antenna coax along side power wires, that is not always the case. It shouldn't be an issue for you, but never say never. If you do have an issue, just shield the coax.

As for front mounted antennas, I am not a fan. It is a personal preference. I don't like antennas banging on my grille, hood or fenders when they hit a tree branch or something else. I also don't like mounting anything in a location that can interfere with my forward vision.

These are my antenna mounts:

 

[OldBuzzard]

Ground-plane antennas (most mobile antennas) are only half of an antenna. They depend on the ground plane to be the other half. The best possibly place for that type of antenna on most vehicles is in the center of a metal roof. That gives a nice dozen-square-foot ground plane around the antenna in all directions. A Wrangler with a ragtop or fiberglass hardtop kills that idea.

The best place in a Wrangler is the center of the hood, or on a large metal plate on the roof. Neither of those is very good for a permanent mount. One possibility, if you don't need to use the radio while driving, is to use a magnet mount and plop it in the middle of the hood when needed.

Unfortunately, most of us want a permanent mount, which almost always ends up at a corner of the body, often with various metal parts partly blocking the antenna pattern. That makes for a very wonky antenna pattern, strongest off in some random direction, and not likely pointing where we want it for whoever we're trying to reach. It's just a sad fact of life.

 

[MikekiM]

So what I am gathering is there is no ideal solution. I’m permanent soft top. I’m not mounting it in the middle of hood, or along the hood side. That leaves me front or rear mount.

Rear seems to have more challenges than front. @Mr. Bills I have the mount you’re using on the driver rear but switched to Trail Tail LEDs so can’t use that mount. That’s what led me to the pipe mount on the carrier.

Front mount seems much better and easier. Shorter run of coax that doesn’t have to sit alongside 12v power. The ground is immediately available. I’m likely to use the ghost antenna most often given the terrain and distances I’m dealing with and never have I had an issue with anything hitting the front of the Jeep. Ghost or shirt whip won’t whip around enough to hit the hood or grill.

Please tell me about how the ground plane impacts reception. Is reception directional based on front or rear mounting? If the antenna is rear mounted with the tub in front of it, is reception forward going to be better? Or more appropriately put, if the antenna is front mounted with the tub behind it, will reception be biased behind the rig?

 

[Zorba]

While @Zorba may think that there can never be interference as a result of running antenna coax along side power wires, that is not always the case. It shouldn't be an issue for you, but never say never. If you do have an issue, just shield the coax.

DC wiring will have exactly zero effect on an antenna. AC wiring might. Properly installed coax is already has a grounded shield. If you have to "shield the coax", you're doing something else wrong. On top of everything else, we're discussing an FM system, which is already immune to induced noise.

 

[OldBuzzard]

Please tell me about how the ground plane impacts reception. Is reception directional based on front or rear mounting? If the antenna is rear mounted with the tub in front of it, is reception forward going to be better? Or more appropriately put, if the antenna is front mounted with the tub behind it, will reception be biased behind the rig?

Generally, transmission and reception will be strongest in the direction of the ground plane. So if your antenna is at the left rear corner, the strongest signals will be toward the right front. You can use that to your advantage when trying to reach a distant radio — point the Jeep's "strong" signal toward it.

DC wiring will have exactly zero effect on an antenna.

Theoretically. Automotive environments are electrically noisy, and RF noise could possibly sneak onto the DC cables. I wouldn't hesitate to run coax next to DC wires. There are so many other electrical noise sources radiating from various systems which can sneak into your antenna.

If you have to "shield the coax", you're doing something else wrong.

True. Although I came across some coax which was so cheaply made that its built-in shield was barely there, letting all kinds of noise through. That stuff needed extra shielding just to make up for the manufacturer going with the lowest bidder.

 

[MikekiM]

Generally, transmission and reception will be strongest in the direction of the ground plane. So if your antenna is at the left rear corner, the strongest signals will be toward the right front. You can use that to your advantage when trying to reach a distant radio — point the Jeep's "strong" signal toward it.

That’s what I thought. Good news is my use case doesn’t require miles and miles of distance. Otherwise I can drive in reverse and maximize the reception.

 

[MountaineerTom]

Someone on here recently (I think) put the small, fat Motorola antenna on a bracket coming off the passengers side A pillar light mount.

How would that work as far as a good signal?

 

[voodooridr]

What about something like this?
https://www.utvsource.com/rugged-ra...term=4576717174644541&utm_content=Ad group #1

 

[Apparition]

What about something like this?
https://www.utvsource.com/rugged-radios-antenna-mount-for-jeep-jl-jk-tj-jt/?sku=UTVS0009908&medium=BING&ad=Shopping&msclkid=874dc4d8caae13302ff1a073e1dd98f7&utm_source=bing&utm_medium=cpc&utm_campaign=Shopping Target ROAS&utm_term=4576717174644541&utm_content=Ad group #1
View attachment 439902

I use that antenna on a Teraflex rear light mount. Works well.

 

[bobthetj03]

What about something like this?
https://www.utvsource.com/rugged-radios-antenna-mount-for-jeep-jl-jk-tj-jt/?sku=UTVS0009908&medium=BING&ad=Shopping&msclkid=874dc4d8caae13302ff1a073e1dd98f7&utm_source=bing&utm_medium=cpc&utm_campaign=Shopping Target ROAS&utm_term=4576717174644541&utm_content=Ad group #1
View attachment 439902

This is where I have mine, and it works fine. just keep in mind, no matter where you mount it, it will be compromised as there just isn't a good place to mount one on a TJ. My Ham radio antenna is mounted on a tail light mount. I can reach a repeater 52 miles away as the crow flies, but if I park my jeep backwards into the carport I can't hit it. Placement is key.

 

[OldBuzzard]

That antenna on the door pillar would work best in a direction diagonally across the hood, and fairly well anywhere across the Jeep, and worst anywhere to the left. Anywhere it has something of a metal ground plane. That's not to say you can't talk to the port side, the signal will just be weaker on that side and the range will be decreased.

Same thing applies to any other configuration. Where the antenna can feel grounded metal under it, it will have a stronger signal.

A typical radio antenna is a dipole — two elements, joined but insulated at the middle, usually pointing in opposite directions. The signal wire (center wire of the coax) goes to one element, and the ground (shield) goes to the other one. In a ground-plane antenna, you bend the down-pointing element up to point horizontally, and then mash it flat into a large thin flat surface. Picture a than flat disk. It's still half of the antenna. Or, in a typical vehicle antenna, you only get the top element, which requires some metal below it to act as the other half. It needs two elements to flow current, just like any other circuit, even if much of that current is in an electromagnetic field around the whole antenna.

 

[Zorba]

That stuff needed extra shielding just to make up for the manufacturer going with the lowest bidder.

Nope. That shit needed to be thrown out and replaced with something decent. I've encountered it a time or two myself.

And yes, vehicles are electrically noisy - VERY! That's why you use coax instead of ladder line!

 

[MikekiM]

Thanks all. Great stuff here.

As I and others have noted, there is no perfect position to mount it. So I am going with what I perceive as the most beneficial.

 

[Zorba]

From an SWR perspective, one of the very best locations is at the front edge of the front fenders. That doesn't necessarily mean the best range, however.

 

[Akitadog]

There used to be Marine antennas that would work without a ground plane to go on fiberglass boats, but it's a compromise.
Does your tire mount have steel bolts thru the tub if so it might be already grounded. VOM would show this.

Most of todays modern auto electronics have built in filtering, which was not the case in radio's of 40 years ago.

 

[OldBuzzard]

There used to be Marine antennas that would work without a ground plane to go on fiberglass boats, but it's a compromise.
Does your tire mount have steel bolts thru the tub if so it might be already grounded. VOM would show this.

Most of todays modern auto electronics have built in filtering, which was not the case in radio's of 40 years ago.

Two ways to make a vertical antenna without a ground plane: One, use the coax shield as the lower element. It actually works pretty good, and is common in large ham radio antennas, but it takes a few extra parts to make it work right. Two, use two elements end to end, mounted vertically, and feed them in the center (a real dipole), which also takes a few extra parts to work right. Marine antennas can go either way. And I think I saw one which used the water as a ground plane, but it has to be salt water.

I've seen "no ground plane" antennas advertised for mobile use, but you have to read carefully to figure out if they will work in a particular situation. Mounting, physical strength, feeding can all be "special" with these.