GMRS / CB antenna locations - near A pillar or mid point on hood

[chorky]

@Radio Guy

I am happy to report that I have a SWR reading of just below 1.5 on CH 1, CH 40 and CH 20. Hopefully some functional testing soon to check signal distance variation between transmitting forward and rearward. Appreciate all the insight you've provided!

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[chorky]

@Radio Guy - question for you lower on this post

So I went for a bit of a highway drive today to get out of the house - first time moving the jeep in almost a month. Anyway, even just on bumpy highway portions I noticed that the center coil of the Stryker CB antenna was moving around a bunch - more than I felt comfortable with. No doubt it was fine - but I just think of stress on the cowl bolts over time.

So I took it off and put on a spring I had purchased from Amazon a while ago - Wilson Antennas 305311SS HD spring. I was going to put this on originally right away but thought to try without it first. I have not yet gone for another drive, but thus far I think it will ease up some of the abrupt stress from bounding around and trying to wiggle that stiff mast.

I also double checked SWR readings after and came up with these - in order from CH 1, CH 40, CH 20

However, when I took the stud off to replace it with the spring, I noticed the underside of the EVO mount (because it is steel) is rusting good already. I did not paint it like I did the GMRS mount on the other side because doing so I was not able to get continuity from the antenna through to the radio end of the coax. So I had to scrape paint off for a good connection. A little surprising and frustrating.

So my question for Radio Guy is - how much negative effect does rust have on radio signal connections and how often should I take it apart to clean and re-check SWR and continuity?

 

[Radio Guy]

@Radio Guy - question for you lower on this post

So I went for a bit of a highway drive today to get out of the house - first time moving the jeep in almost a month. Anyway, even just on bumpy highway portions I noticed that the center coil of the Stryker CB antenna was moving around a bunch - more than I felt comfortable with. No doubt it was fine - but I just think of stress on the cowl bolts over time.

So I took it off and put on a spring I had purchased from Amazon a while ago - Wilson Antennas 305311SS HD spring. I was going to put this on originally right away but thought to try without it first. I have not yet gone for another drive, but thus far I think it will ease up some of the abrupt stress from bounding around and trying to wiggle that stiff mast.

I also double checked SWR readings after and came up with these - in order from CH 1, CH 40, CH 20

However, when I took the stud off to replace it with the spring, I noticed the underside of the EVO mount (because it is steel) is rusting good already. I did not paint it like I did the GMRS mount on the other side because doing so I was not able to get continuity from the antenna through to the radio end of the coax. So I had to scrape paint off for a good connection. A little surprising and frustrating.

So my question for Radio Guy is - how much negative effect does rust have on radio signal connections and how often should I take it apart to clean and re-check SWR and continuity?

That looks like a lot of antenna for that type of mount. Anyway, rust in this case is mostly cosmetic. I can't imagine the rust getting bad enough to cause a high resistance connection unless you ignored it for many years. If you had to scrape the paint to make electrical contact I would try to clean, prime and paint the bare metal or at least goop it up with something water proof to keep the rust at bay.

 

[chorky]

That looks like a lot of antenna for that type of mount. Anyway, rust in this case is mostly cosmetic. I can't imagine the rust getting bad enough to cause a high resistance connection unless you ignored it for many years. If you had to scrape the paint to make electrical contact I would try to clean, prime and paint the bare metal or at least goop it up with something water proof to keep the rust at bay.

Yeah I wasn't happy with how much it was moving around with the mast directly to the mount. I do wish there was a mount that incorporated the windshield hinge and both cowl bolts but haven't found anything like that, so because I have the cowl lights - this is really the only choice. It's a lot surlier than just a fender or hood mount though that's for sure.

maybe somebody here with fab skills wants to make me a set of alum ones for each side?????? paging fabricators

Hmm...what about dielectric grease? It's electrically conductive and designed to help prevent water rusting out contacts of insides of connectors. Probably shoulda used some of that right away. I'll probably take it apart in a few weeks when I can get some sand paper, clean it up, and grease away.

 

[Radio Guy]

Yeah I wasn't happy with how much it was moving around with the mast directly to the mount. I do wish there was a mount that incorporated the windshield hinge and both cowl bolts but haven't found anything like that, so because I have the cowl lights - this is really the only choice. It's a lot surlier than just a fender or hood mount though that's for sure.

maybe somebody here with fab skills wants to make me a set of alum ones for each side?????? paging fabricators

Hmm...what about dielectric grease? It's electrically conductive and designed to help prevent water rusting out contacts of insides of connectors. Probably shoulda used some of that right away. I'll probably take it apart in a few weeks when I can get some sand paper, clean it up, and grease away.

The grease used externally is not permanent, it will eventually fail. I think any metal shop can duplicate that shape out of 1/8" thick stainless without too much trouble. You might have to live with a slightly larger bend radius but it won't affect anything.

 

[Lumis]

What do you think about here? 1 GMRS and 1 Ham.

 

[49Gramps]

They look a bit too vulnerable when off-roading.

 

[Real Jeep]

On my new 2023 Gladiator I did this mount

The post below was a right up I did on the JK-Forum way back in 2012 with updates.

I work in the two-way radio business in New Mexico

I did 2 JKU builds before trading up for the Gladiator JT Rubi Diesel.

As a commercial radio tech the placement of the antenna near the N in the Rubicon Sticker is a great place as its away from the A-Pillar thus cutting down on reflecting from it and gets it out in the open. For many trucks that can't have an antenna on the roof for what ever reason, ladder rack, fiber glass or low garage, this is the optimal placement away from cargo areas.

Down side it could get snagged by trees so as I explain in my JK post its all comes down to performance vs "Jeeping lifestyle".


*****Updated January 22, 2016 *****

Jeep Antenna Placement Recommendations. CB ~27 Mhz, HAM 140-148 440-450 Mhz and Commercial 150-170 450-470 and 800 MHz Frequencies. For low 3 to 7 Mhz HAM antennas I’m not covering that here as those are special antennas and if you have a license for those frequencies then you already know what your doing.

I have been looking around the forum at the descriptions for antenna placements and there is some good advice out there, but not all in one place so I have decided to make an easy English description for those not so tech savvy. Please keep in mind that this post is to describe the best balance of function and looks. Granted putting an antenna in the middle of the hood is a great transmit spot but it’s in your field of view and makes the Jeep look like a unicorn.

Background: I am a commercial two-way radio tech with Ham and marine licenses. I have been doing installs for about 21 years. Like police cars, ambulances utility trucks and the like.

Guidelines to follow and these are relative to your situation. For example: if you park your Jeep in the garage you can’t put your antennas on the roof rack so the cowl is you next best thing.

Guidelines:

1 The longer the better. (Relative to your situation if you have 5000 foot peaks that have repeaters a small antenna like mine will work fine, but if you need to talk on a simplex/direct frequency the longer the better.)
2 The largest horizontal ground plane the better. A horizontal ground plane is exactly that a flat piece of metal or metal spikes going off in 4 directions from the base of an antenna. (See exception to this guideline later in this post)
3 The farther away from vertical flat metal the better.
4 Keep the antennas separated a foot or even more is better. Keep VHF 150 Mhz away from the stereo antenna. If you using a scanner that does not transmit then that’s ok next to the stereo antenna.
5 Avoid Bumper and license plate mounts if possible.
6 DO NOT PUT YOUR ANTENNA BETWEEN THE TAIL GATE AND THE SPARE TIRE
7 DO NOT PUT YOUR ANTENNA BETWEEN THE TAIL GATE AND THE SPARE TIRE
8 Just to make sure you are reading this correctly DO NOT PUT YOUR ANTENNA BETWEEN THE TAIL GATE AND THE SPARE TIRE. Read below for a more detailed explanation on this.

I will put the easy answers here at the top with more detailed explanation at the bottom for those interested. Listed here are the best to worst places to place antennas at the bottom I will also talk about other types of antennas that I don’t have images of.

1st On top of the center of a roof. If you never plan on taking off the hard top off then the things you can do are place a large piece of metal under the roof, attach the antenna to a roof rack or get a no-ground plane antenna (guideline # 2 exemption).

2nd On the cowl. Must effective place after the roof and it allows you to have longer antennas and still make it in the garage. Also is good for those that don’t want to drill holes in their body. I have 5000 foot mountains so I don’t need a long antenna.

Seen here is my small dual-band antenna for HAM use.

Note: if you need to place more antennas on the cowl try to avoid VHF 150Mhz near the stereo antenna as transmitting near that antenna will cause noise on your car radio.

3d on the corner of the Jeep. This is preferred over the bumper because it gets the antenna up above the body metal line. You will see the light bar from Olympic in this shot and they advertise it as a place to put antennas. This may be okay as it’s away from the body of the Jeep. Seen here is my commercial 800 MHz antenna looks like the one in front but its coil is in a different place.

4th Bumper: You see an Olympic bumper here with a hole for CB antenna This is OK but not Ideal as the base is still below wall of steel on the body. A license plate mount would have the same problem.

5th Between the tailgate and the Spare tire. As I said before DO NOT DO THIS UNLESS ABSOLUTLY NESSARY. AND DEFINITELY NOT FOR HAM OR COMERCIAL FREQS. Besides being the most inefficient place for and antenna one can’t open the window and close the tailgate.

More detailed stuff.

The Jeep Wrangler presents us with a problem it’s a convertible with no metal roof. Two-way radio antennas weather they be CB, HAM or Commercial need to breathe. I.E. it needs to be exposed to air with as little horizontal metal next to them as possible. It also needs a ground plane under it. Ideally the ground plane should be a diameter equal to ½ of the wavelength of the frequency. So a 150 Mhz antenna would have a diameter of about 38 Inches CB would be about 6 yards NOT TO BE FOUND ON A JEEP.

The nice engineers that make antennas use coils and such to compensate for this. Here is where our unique problem lies these coils need to be exposed to the air and not near horizontal metal as much as possible. Nearly all ham and commercial antennas have coils and they are at the bottom of the antennas. So placing them on the bumper right next to the body will cause the radiation to be reflected back in to the radio which over time will damage the power amplifier in the radio. The cowl and the higher rear corner placement is desired because the roof is made of fiber glass and the radiation will just pass through it. Yes there are pillars and roll bars but the radiation will bend around them verses being reflected back.

The tailgate and spare tire situation yes, I know all our favorite web venders sell tailgate antenna brackets but they should only be used as a last resort. And again I know in caravan style on the trail they work fine and Jeepers have been mounting them there for years but …

This is why they’re bad. Remember the base of the antenna must be exposed as well as the whip. Think of a nuclear bomb going off the gamma rays can’t pass through 1 inch of lead or 10 feet of concrete and in our case of two-way radio signals the tailgate and spare tire are acting like a sandwich keeping our radiation inside and not allowing it to escape. I started here just because I thought it was cool looking. However mounting the antenna here proved to be fatal. Basically I had two pieces of large solid metal surrounding my antenna base causing massive reflected power going back into my radio and not radiating out. I used a watt meter to measure what was happening. Some of you out there may have access to something called an SWR meter and that’s fine if you know how to use it, it will tell you the same things. I use watt meters because I need to know how much power is coming out of my radios for commercial purposes to satisfy FCC rules. Ideally if you have a 30 watt VHF radio you want 30 watts transmitted out with as little reflected back as possible. 30 watts with say less than 2 reflected is great. I had 25 watts with 20 reflected. The more reflected back will also adversely effect the power out which is why I had the lower number on output. After tuning my antenna to 30 watts with 2 reflected the antenna went from about 50 inches to about 30 inches making it nice long high gain antenna useless. And of course one can’t open the back window and close the tailgate without removing the antenna thus making that random trip to the hardware store for 2x4’s a bit of a problem without a roof rack.

For those of you who mount your antenna base above the spare tire with an extension there is still the problem of a ground plane unless you use say the Olympic light bar or make a bar of some sort you end up with the same problem. There is an exception to this rule as mentioned in guideline # 2 above and that is a no-ground plan antenna they do exist for CB, HAM operations and radio towers. Of course you could use one on the fiberglass Jeep roof too but then you can’t take the top off or get into the garage. Just remember keep the base as well as the whip away from vertical flat metal. Like the tailgate spare tire and body. Pillars and roll bars are ok but try to keep the antenna as far away from them as possible too.

Other antennas that you may have seen or many want to use:

1 On-glass antennas, I have used them but they are not great. They don’t have a good ground plane and lots of reflected power. I would avoid if possible.
2 I would also avoid dual-purpose antennas like ones that use the car stereo antenna as a VHF antenna with a splitter box one to your stereo and the other to the Two-Way. Not to be confused with dual-band antennas that’s different and used for HAM Frequencies.
3 Side ball mount antennas, used for CB and military frequencies. As long as they are mounted to the highest point on the body the better. You may have seen these long whips that bend down to the front of the Jeeps. This served two purposes that I know of one was so the whips did not hit the trees in the jungles and the other was to make the radio talk shorter distances. See at 100 Mhz the radio waves pass through the atmosphere below that they bounce back to earth commonly known as skip. The whip standing vertical could skip from New Mexico to Louisiana but bent over It could talk from one side of New Mexico to the other. This all of course depends on frequency, power time of day and sun spots.
4 Magnetic antennas, these are good for the temporary weekend trip as long as they attached to a good solid piece of metal. I would not recommend them for permanent mount as usually the coax is put through a window or doorframe and will eventually get damaged.

Here is an image of different radiation patterns. I don’t have an image for what it would look like for the tailgate and spare tire but basically the signal isn’t going very far. The center image shows the most ideal relatively round even pattern. The corner mounted antenna show what happens when the antenna only has a ground plane on two sides and not 360 degrees.

*** MORE TECHNICAL UPDATE ***

I conducted an experiment using a Commercial grade CB antenna Made by Tram with an NMO mount. I tested it on the Cowl, Rear Corner, Rear bumper and the rear light bracket with an SWR Meter. In the pictures you will see a bulkhead mount that I used. I used one on the light bar with and with out extra radials to see if it would improve the readings. I don’t have any “fire stick” style antennas and those may get a lower SWR reading however I believe my experiment shows the basic difference in performance one can achieve on the different locations of the Jeep.

Readings

Cowl SWR 1.2 result Great
Rear Corner SWR 1.5 result Good
Light bar with and without the extra radials SWR ~2.0 result Not the best
Bumper SWR 3+ Result Very Bad.

NMO Bulkhead mount

NMO Bulkhead mount with radials

NMO Bulkhead mount on bumper

NMO Bulkhead mount on bumper

*** MORE TECHNICAL UPDATE *** 11-12-14

Recently I cracked my intake manifold changing a censor. I had my mechanic add some headers and new spark plugs at the same time he replaced the manifold. Needless to say by doing so we disturbed the electrical system of the Jeep thus causing RF (Radio Frequency Radiation) leakage. It sounded like bacon frying on my VHF and UHF analog ham channels all across the spectrum, both receiving and transmitting.

To solve this problem I ended up swapping my dual band VHF/UHF antenna from the Cowl to the back and put my 800 MHz antenna on the Cowl. This got the antenna enough away to solve this problem.

But a new problem was also discovered. My 800 is a commercial digital radio and although the digital signal did not pick up the “bacon frying noise” it made the radio less sensitive.

To solve this problem I tried to put a brand new coax with new antenna and connector, SWR checked great. But that did not work so I ended up relocating my 800 antenna to the rear light bar bulkhead mount as seen in the above pictures. Once there my receive signal strength came back.

 

[chorky]

I thought I would follow-up on this thread since I noticed something interesting. Midland has a new line of antenna products. They also FINALLY include some infographics to depict the different applications, pros and cons. It's about time a radio manufacturer does something like this to help folks understand the non technical things, even though it's technical. I like how they included graphics to show the different effects of gain, but ALSO included a hilly terrain situation as well to further help folks understand. This is one of several reasons I also have CB with a whip antenna.

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