CB Antenna mount idea [Archive] - JKowners.com : Jeep Wrangler JK Forum

: CB Antenna mount idea


TekWarren
03-06-2008, 06:32 AM
Yes I posted this on "other" forums also and so far with zero response. Anyway I'm having a thought and would like some opinions from the experienced minds here.


I've been looking heavily at the different options for mounting, brackets, lots of pictures here etc. While I was out in the garage tonight thinking I was going to accomplish something with an old magnetic mount antenna that I have taken apart discarding the magnetic base I considered a mounting location I haven't yet seen used.

Initially I thought I would do something on top the 3rd brake light housing...but there is definitely not enough room to route coax down through it much less have any sort of supporting stud fit in with the light fixture.

My next thought: Why couldn't a simple bracket be made to piggy back the 3rd brake light housing...I'm thinking a simple piece of aluminum that is held in place by the same screws behind the brake light...maybe upgraded screws for better security. All I'm looking for is a small platform I drill into and mount a short antenna.

Here's where I need some expert opinions:

I am thinking no more than 2-3ft antenna so there would be very little weight or tension being supported by the 3rd brake light "arm". Additionally at this vantage point a spring mount would have much more room for movement than if it was mounted in a lower location on the wheel carrier.

By having a higher mounting location this eliminates the "need" for a such a long antenna that I am commonly seeing. It seems to me that much of the long antenna's capability to send and receive is blocked off by vehicle itself and only the top most portion clearing the vehicle will have the best range for send/receive. (I am no radio expert so chime in here).

Is there an advantage to having an antenna mounted say from the license plate holder that clears the top of the Jeep by 6" as apposed to using a shorter antenna mounted higher that also clears the jeep by 6" ??

In my rough measuring tonight (it was dark and i was not precise) it looks like I could clear the top of my soft top by 6-7" or more with a mere 2' antenna if it where mounted with the method I am suggesting.

Again comes the question of overall antenna length versus actual 360 degree clearance from the vehicle.

The whole tire carrier including the arm for the 3rd brake light is aluminum so its fairly sturdy and if using an aluminum bracket/platform with a short spring mounted antenna (or one that is very flexible) it seems like you have a win-win situation...but I need your experienced minds to break down anything I'm missing.

I have a couple places I think I can get scrap aluminum for free, maybe even the holes drilled for me also....one source is even leasing a JK! I might be doing some emailing tomorrow to see what I can get unless someone scares me away from even trying this as a mount location.

Thanks in advance.

igofshn
03-06-2008, 07:06 AM
I don't think the 3rd brake light would be strong enoug. The tension of the antenna in the breeze could possibly make it crack. It isn't designed for any tension.

skibum
03-06-2008, 07:15 AM
I think the spring mount (and the short antenna) would mitigate any (most?) problems associated with tension on the aluminum third brake light housing. I'm not a mechanical engineer, but I used to play one on television (kidding, but I was a project manager for a Navy nuclear shipyard), and I have a fair bit of experience with dynamic loads, stress risers and otherwise jackleg engineering. That said, I could be wrong. :D

As to height of antenna, I am barely CB literate but if its anything like marine VHF, the signal is "line of sight" so equal height should mean equal performance.

Just my .02 (and probably worthless) but at least we responded (unlike that other place). :stirthepot:

BigO
03-06-2008, 07:58 AM
If you do figure out a way to get the antenna mounted on the brake light, you're going to have to come up with a way to ground it. Or you'll have to get a no-ground antenna, like the kind you'd use on a boat. The brake light bracket is plastic and the tire carrier is aluminum. Both are not good for a ground.

Also, those spring mounts are flexible when mounted to a solid surface, but I'd be afraid to mount one to plastic. I'd bet it would eventually crack the plastic if the antenna gets bent a lot.

Whatever you come up with, at least the top 6" of the antenna should be above the top of the Jeep for best reception/transmission.

TekWarren
03-06-2008, 08:08 AM
Thank you both for your thoughts. I'm not disputing just trying to understand...but the arm for the third brake light "feels" very sturdy to me. It seems that only a very long antenna with some pretty heavy whipping action or tree snagging could even make this arm move or stress it. Do you think a short 2-3" footer with a spring will stress it that much? I would definitely not consider this location without a spring. -I'm no engineer either that's why I carefully used the words "feels like" and "seems like" LOL.

I know the magnetic mount antenna I'm playing with would be no issue from this mount point. It's just over 2ft long, very light and the top portion of the antenna is so thin that it whips easily...also has a spring base. This is the usual magnet mount you would find at walmart and the such...I am having a heck of a time finding the more sturdy hard mount antennas...finally found a radio shack that had some but they are white and I want black if I go that route.

Anyway...thanks and keep the comments coming.

TekWarren
03-06-2008, 08:13 AM
If you do figure out a way to get the antenna mounted on the brake light, you're going to have to come up with a way to ground it. Or you'll have to get a no-ground antenna, like the kind you'd use on a boat. The brake light bracket is plastic and the tire carrier is aluminum. Both are not good for a ground.

Also, those spring mounts are flexible when mounted to a solid surface, but I'd be afraid to mount one to plastic. I'd bet it would eventually crack the plastic if the antenna gets bent a lot.

Whatever you come up with, at least the top 6" of the antenna should be above the top of the Jeep for best reception/transmission.


Thanks for the advice...not to question your knowledge but I thought the brake light "arm" was the same material as the tire carrier. Last night I had the 3rd brake light removed and the light housing is definitely plastic...I would not use that as a mount and it wouldn't work anyway. I'm talking about using the existing two screws (top) that hold the light in place on the arm to also hold up a small aluminum platform.

BigO
03-06-2008, 08:16 AM
The aluminum would be a problem for the ground. You need bare steel.

As far as the actual mount, I say give it a try and see what happens. We're just taking guesses here regarding the sturdiness.

Bigjerm
03-06-2008, 08:20 AM
this is what I did. I bought a bracket thatís made to mount on the mirror of 18-wheelers. It consist of 1 piece of metal that has a 90 degree bend and then another piece that bolts onto it to go around the curve of the mirror bracket. Well I took the 90 degree piece, drilled a hole big enough for one of the spare tire carrier bolts to fit through and I bolted it back up. I then drilled a small hole under the carpet inside the back of the Jeep and put a bolt through with a wire attached and ran the wire to the antenna bracket and secured it with another bolt. Then i put on the spring mount and a 4' fire stick whip and it clears the top plenty. I probably could have gone with a 3' and still had 6" above the roof.

Ill try and get some pictures today of my CB mount and antenna mount

John L
03-06-2008, 08:37 AM
Interesting idea. I wouldn't go any shorter than 3'. Definately use a spring and sturdy stud mount. Run a braided ground strap from the gate to the body to ensure a good ground.

Ultimately, the 102" stainless whip coupled with a 6" spring is the best system. This is because 108" is a very close approximation to the 1/4 wavelength of the center of the CB frequency range. Shorter antennas are electrically the same length, but physically shorter. They do this by winding the excess in a coil. Top loaded coil antennas are usually the second best type to run, that's why the top of the antenna needs to be above the roofline. That way the majority of the radiated signal is able to leave the antenna efficiently.

I hafta kinda disagree with the statement that aluminum is not good for a ground. I have my antenna (3' Firestik Firefly) mounted to the tire carrier with a stud, no spring, on the flat part of the carrier in front of the 3rd brake light. Fortunate for me, my wheels have enough offset to allow this mounting position. I have had no problem at all with this setup, I have less than 5 ohms resistance between the mount location and the frame/body.

The only thing I have to do to keep the system running well is occasionally take the stud mount off the carrier and scotchbrite the contacting surfaces. The two dissimilar metals (aluminum and stainless) contacting each other create a galvanic corrosion situation, essentially making a battery. If not kept in check, it will eat the aluminum away. Maintain the area and you will have no problems.

I have also run my 102" whip on the tire carrier at highway speeds with very good results. A spring does me no good with this mounting position, the antenna flexes either at the contact point on the tire or the 3rd brake light.

BTW, my SWR with the 3' is 1.2 at 19, 1.6 at 1 and 40. It's 2.1 flat with the 102" whip.

I think it's a good idea worth trying out. If you try this, keep us updated.

BigO
03-06-2008, 09:37 AM
I hafta kinda disagree with the statement that aluminum is not good for a ground. I have my antenna (3' Firestik Firefly) mounted to the tire carrier with a stud, no spring, on the flat part of the carrier in front of the 3rd brake light.

No kidding. I should have messed with that to see if it works before I bought an antenna bracket a while ago. Maybe the aluminum they use for the carrier is an alloy with a lot of copper in it.

TekWarren
03-06-2008, 09:45 AM
Thanks again for the replies.

I fully agree with you on the 102" whip...back in high school I had one on a truck I drove and the distance I could clear with antenna was simply amazing. I have/had swr tuner, once I decide on this mounting situation I'll have to try and find the unit...and remember how to use it!

A small part of this idea came from consideration for clearing my garage. I don't have a whole lot of room upon entry but once inside I would be fine. I either need some decent flex...and would be dragging the antenna tip daily, or a quick disconnect, or with a spring mount maybe I can come up with a simple strap solution that anchors the antenna out of the way unless in use.

I have sent a email including a crude drawing to one of the shop teachers in the school district I work for to see if he has any scrap aluminum I can snag...if he does not I have two other sources I'm pretty sure I can get material from. I'll keep the topic updated if I progress. :)

John L
03-06-2008, 11:00 AM
Thanks again for the replies.

I fully agree with you on the 102" whip...back in high school I had one on a truck I drove and the distance I could clear with antenna was simply amazing. I have/had swr tuner, once I decide on this mounting situation I'll have to try and find the unit...and remember how to use it!

A small part of this idea came from consideration for clearing my garage. I don't have a whole lot of room upon entry but once inside I would be fine. I either need some decent flex...and would be dragging the antenna tip daily, or a quick disconnect, or with a spring mount maybe I can come up with a simple strap solution that anchors the antenna out of the way unless in use.

I have sent a email including a crude drawing to one of the shop teachers in the school district I work for to see if he has any scrap aluminum I can snag...if he does not I have two other sources I'm pretty sure I can get material from. I'll keep the topic updated if I progress. :)

Clearance in my garage is my issue as well, when i run the long whip i have to use a quick disconnect and take it off before entering. I gotta say, though, that big whip looks awesome on the Jeep, like a giant R/C Jeep. It gets alot of looks.

I've been playing with the idea of putting an antenna mount on top of the soundbar. It would be an ideal location in relation to the ground plane and would radiate in more of an omnidirectional pattern. Mounted in the rear center of the vehicle gives a pattern that is forward biased.

The mount to the bar would be easy, but would require careful trimming and subsequent re-sealing of the freedom tops. It wouldn't work for the soft top crowd. I found a locking swivel that allows the antenna to lay down on the roof for low clearance situations, so you wouldn't even have to take it off.

I am going to try a Wilson mag mount in that location this summer with the top off, should work well.

Keep in mind if you use the antenna portion of your mag mount that the ground system is different, it depends on capacitance coupling, not a direct ground. 3' firestiks are cheap at about 17.00, you may think about going that route.

Good luck with your idea!!

John L
03-06-2008, 01:11 PM
No kidding. I should have messed with that to see if it works before I bought an antenna bracket a while ago. Maybe the aluminum they use for the carrier is an alloy with a lot of copper in it.

Yeah, it works quite well. I check resistance every once in a while and it stays very low. I'm with you though, ususally the cast stuff is crap.

TekWarren
03-06-2008, 06:23 PM
Well no luck from the shop teacher this afternoon, all he had was sheet metal and I want something a little stronger than that. My last job was supporting a vocational center so my next point of contact was going to be the welding teacher, he always has scrap aluminum pieces...However if I can get an accurate enough drawing/description I am now thinking about contacting the machine shop teacher. I'm not sure which or maybe both to contact. On one hand all I need is a 6" long or so chunk folded with a right angle...I can clean it up and paint it later once I know if it will work or not.

PhilD
03-07-2008, 09:37 AM
I know next to nothing about antenna ground planes, but FWIW aluminum is an excellent conductor of electricity, better than copper.

TekWarren
03-07-2008, 06:32 PM
My father in-law was over tonight and he is about the best man for any type of job be it wood, metal, or whatever. He said he could definitely find something for me to try when I explained my idea :bounce:


Not that I want to turn this into another antenna grounding thread but I'm getting confused on what some of you are saying. It sounds like one guy is saying the tire holder sucks as a ground and another is saying it's fine...yet they agree with each other even though their comments conflict ...

PhilD
03-07-2008, 06:46 PM
Not that I want to turn this into another antenna grounding thread but I'm getting confused on what some of you are saying. It sounds like one guy is saying the tire holder sucks as a ground and another is saying it's fine...yet they agree with each other even though their comments conflict ...If the requirement if a ground is to be a good conductor, then it will work just fine.

BigO
03-07-2008, 07:00 PM
I know next to nothing about antenna ground planes, but FWIW aluminum is an excellent conductor of electricity, better than copper.

If using aluminum wire for a house ground, it would have to be larger than a copper wire used to carry the same load. Silver, copper, and gold have less resistance than aluminum. I don't want to stray off of the topic here. All of this can be looked up elsewhere. According to John L, the cast aluminum (and whatever else is mixed in) tire carrier is fine for a ground. :D

Back to your regularly scheduled antenna mount idea.

PhilD
03-07-2008, 08:10 PM
If using aluminum wire for a house ground, it would have to be larger than a copper wire used to carry the same load. Silver, copper, and gold have less resistance than aluminum. I don't want to stray off of the topic here. All of this can be looked up elsewhere. According to John L, the cast aluminum (and whatever else is mixed in) tire carrier is fine for a ground. :DOkay, I may have been a bit quick in my defense of the aluminum industry ;) But it's still a very good conductor, although I like the idea of people having gold tire carriers :smokin:

BigO
03-07-2008, 08:31 PM
Okay, I may have been a bit quick in my defense of the aluminum industry ;) But it's still a very good conductor

You're right, pure aluminum is. My concern with the tire carrier is (was) that it's an alloy. John L confirmed that the aluminum alloy mix is a sufficient conductor.

John L
03-08-2008, 05:20 AM
Here's what my setup looks like. Some folks have used the tabs for mounting also.

http://i152.photobucket.com/albums/s173/tailgater3/studmountlocation.jpg


http://i152.photobucket.com/albums/s173/tailgater3/antinstalled.jpg


http://i152.photobucket.com/albums/s173/tailgater3/clearance.jpg

Crankbrother
05-18-2008, 11:11 AM
I like your set up John L that is what i had in mind for mine now I know how good it will look.

John L
05-18-2008, 11:57 AM
I like your set up John L that is what i had in mind for mine now I know how good it will look.

Just keep in mind that this will not work with the stock spare, there isn't enough backspacing for access to this area of the carrier.
I measured .920 back from the slot edge. This put the antenna slightly against the spare, and kept it about .250 off the 3rd brake light.
I recommend measuring carefully and do a mockup to keep the antenna balanced space-wise between the light and tire. I've since removed the 3rd brake light and now wished I would have left airspace between the tire and antenna. Still, no big deal it still works great, that's what matters.
Good luck, and don't forget to ground the gate to the body with a braided ground strap.

YmansJK
05-19-2008, 05:54 PM
This is what I am doing for a antenna mount. I already broke my license plate holder so I was going to get some warrior 3/16" black corners with holes than make a plate that fills the license plate bracket hole with a 90 and hole to mount my antenna. I will have nice solid corners and a antenna mount. Should be pretty sweet if I ever get around to it. The corners are cheap and strong. Better than AEV's 1/8" corners

mrsig
05-20-2008, 06:26 AM
Just make a bracket for the top hinge like I did and go with a 3í K40 Whip Antenna.
http://www.aaof.us/images/cb1.jpg

http://www.aaof.us/images/cb2.jpg

http://www.aaof.us/images/BI0419088.jpg

Big A
05-20-2008, 11:30 AM
And here is my solution! :)

http://www.jkowners.com/forum/showthread.php?t=1465

Bigjerm
06-05-2008, 03:26 PM
Ok long overdue here but I finally got pictures. On the spare mount.


http://i72.photobucket.com/albums/i189/JermTib05/Jeep/DSC_0429.jpg




CB Radio mount:

http://i72.photobucket.com/albums/i189/JermTib05/Jeep/DSC_0430.jpg
http://i72.photobucket.com/albums/i189/JermTib05/Jeep/DSC_0431.jpg

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09-21-2008, 10:19 PM
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KD6QZX
09-26-2008, 06:26 PM
MRSIG, could you post a close up pic of your antenna mount, I need this location for a biger Amature Radio Antenna (ATAS100) I have the radio with a remote face installed (radio under passenger seat and face abouve mirror with 2 sided tape).