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-   -   Question for those with CB antenna mounted on Tire carrier (http://www.wranglerforum.com/f40/question-for-those-with-cb-antenna-mounted-on-tire-carrier-143870.html)

Sbroadus 03-03-2012 02:53 PM

Question for those with CB antenna mounted on Tire carrier
 
I have mounted my antenna on tire carrier and SWR is about 1.6 when I open the tailgate and swing it open it goes down to 1.1. I can't seem to get it any lower than 1.6 with the tailgate closed. Any suggestions? It's no closer to the jeep than others that are mounted with tail light mounts.

psouza 03-03-2012 05:57 PM

Quote:

Originally Posted by Sbroadus (Post 2098733)
I have mounted my antenna on tire carrier and SWR is about 1.6 when I open the tailgate and swing it open it goes down to 1.1. I can't seem to get it any lower than 1.6 with the tailgate closed. Any suggestions? It's no closer to the jeep than others that are mounted with tail light mounts.


I am set up the same way as you. And have the same observations. I don't consider it a problem. We are up against the laws of physics. As the tire carrier is closed and the antenna approaches the body, the antenna loading changes. Two things happen at the same time. First the antenna center frequency resonance point increases in frequency by about 50 to 80 KHz. This can be tuned out, reducing the VSWR. Second thing is the loading, from being too close to the body, changes the impedance of the antenna (not frequency related) and thus can not be tuned out. Relocating the antenna is a possible remedy. 1.6 to 1 is pretty good. Any one with the same configuration who claims substantially better is either lying or in error.

C.L. 03-03-2012 06:02 PM

Part of it may also be your ground. When most tire carriers are closed, they are sitting on a teflon pad or powder coated/painted latch; the bearing is unloaded and centered in it's grease cup. When you swing it open and really load the hinge, it's bearing assembly is more likely to make metal/metal contact to the rest of the vehicle.

Sbroadus 03-05-2012 02:41 PM

When I get a chance I'm going to try and run a seperate ground and see how it affects the SWR and I will let you know the outcome. I know we aren't the only ones with this problem. Thanks for the ideas.

Maro35089 03-13-2012 10:09 PM

I am running a 103' whip off of a mount on the tire carrier and my swr is around .5 or less with no added ground.

the rock99 03-14-2012 07:20 AM

Quote:

Originally Posted by Maro35089
I am running a 103' whip off of a mount on the tire carrier and my swr is around .5 or less with no added ground.

It is impossible to have an swr of less than 1:1

30-284 03-15-2012 09:17 PM

Quote:

Originally Posted by the rock99 (Post 2138648)
It is impossible to have an swr of less than 1:1

Especially with a 103' antenna, that's much too tall.:D

Donn

Remus_Redbone 03-15-2012 11:09 PM

Quote:

Originally Posted by 30-284 (Post 2145007)
Especially with a 103' antenna, that's much too tall.:D

Donn

102" stainless steel whip with a 6" spring is the most efficient mobile antenna for 11 meter / CB. It's not at all too tall, it's exactly 1/4 wavelength for ~27 MHz / CB frequency

Those 3 and 4 foot fiberglass antennas most folks run have 108" of wire wrapped around them so they will be the electrical equivalent of 1/4 wavelength of 27 MHz but they are not anywhere near as effiicient as 9 longitudinal feet of stainless steel wirestock like a 102" steel whip.

"Too tall" would be a full wave antenna, which would be approximately 36 feet.

The Toolman 03-15-2012 11:23 PM

Quote:

Originally Posted by Remus_Redbone (Post 2145441)
102" stainless steel whip with a 6" spring is the most efficient mobile antenna for 11 meter / CB. It's not at all too tall, it's exactly 1/4 wavelength for ~27 MHz / CB frequency

Those 3 and 4 foot fiberglass antennas most folks run have 108" of wire wrapped around them so they will be the electrical equivalent of 1/4 wavelength of 27 MHz but they are not anywhere near as effiicient as 9 longitudinal feet of stainless steel wirestock like a 102" steel whip.

"Too tall" would be a full wave antenna, which would be approximately 36 feet.

Exactly :thumb:

Thanks for picking up my slack Redbone, been way busy & overlooked some of the radio & antenna questions.

Guys, Remus has given you the best antenna info to receive, as far as CB goes, IMHO :thumb:

sparky 03-16-2012 01:18 PM

You missed the point. Details, men, details.

30-284 is correct.

A 103' antenna is too long. It's also a driving hazzard.
Now a 103" sounds pretty good.

Mel143 03-16-2012 04:06 PM

[QUOTE=Remus_Redbone;2145441] Those 3 and 4 foot fiberglass antennas most folks run have 108" of wire wrapped around them so they will be the electrical equivalent of 1/4 wavelength of 27 MHz but they are not anywhere near as effiicient as 9 longitudinal feet of stainless steel wirestock like a 102" steel whip.
[QUOTE]

I just ordered the Rugged Ridge bracket for mounting a CB antenna on the spare. Just picked up a Midland 75-820. People seem to like the radio, but the factory antenna's useless in the truck. I still need the antenna, but want to keep it to the 3-4' size.

Don't need killer range, but would like to get out as good as possible for caravans, light off-road, local info, etc. Any recs on the brand or model of antenna we should look at? Thanks.

The Toolman 03-16-2012 04:59 PM

Quote:

Originally Posted by sparky
You missed the point. Details, men, details.

30-284 is correct.

A 103' antenna is too long. It's also a driving hazzard.
Now a 103" sounds pretty good.

:rofl: You are correct there sir

Remus_Redbone 03-16-2012 08:35 PM

I'm catching' on now. Yep, 103' would be more like a double wave dipole.....

Remus_Redbone 03-16-2012 10:31 PM

[QUOTE=Mel143;2147483][QUOTE=Remus_Redbone;2145441] Those 3 and 4 foot fiberglass antennas most folks run have 108" of wire wrapped around them so they will be the electrical equivalent of 1/4 wavelength of 27 MHz but they are not anywhere near as effiicient as 9 longitudinal feet of stainless steel wirestock like a 102" steel whip.
Quote:


I just ordered the Rugged Ridge bracket for mounting a CB antenna on the spare. Just picked up a Midland 75-820. People seem to like the radio, but the factory antenna's useless in the truck. I still need the antenna, but want to keep it to the 3-4' size.

Don't need killer range, but would like to get out as good as possible for caravans, light off-road, local info, etc. Any recs on the brand or model of antenna we should look at? Thanks.

I bought a 4' Wilson Fiberglass w/ adjustable tip back in Jan that's been great. It has a feature I haven't seen before that I guess came about while I was out of the radio hobby for years. It has a "matching lead" you can connect to ground that shifts the resonance of the antenna, so if you are mounting it on fiberglass or using in some other non-metallic application, it will help you get it in tune. $19.95 at the local truck stop w/$5 mail-in rebate. Francis and K40 also make good stuff. The Wilson I bought is STIFF, so if you mount it where it's going to hit brush, it will recoil enough to whack the heck out of something. I 'm running mine with a straight spring just so it will give a little.

Mel143 03-18-2012 02:11 PM

I bought a 4' Wilson Fiberglass w/ adjustable tip back in Jan that's been great. It has a feature I haven't seen before that I guess came about while I was out of the radio hobby for years. It has a "matching lead" you can connect to ground that shifts the resonance of the antenna, so if you are mounting it on fiberglass or using in some other non-metallic application, it will help you get it in tune. $19.95 at the local truck stop w/$5 mail-in rebate. Francis and K40 also make good stuff. The Wilson I bought is STIFF, so if you mount it where it's going to hit brush, it will recoil enough to whack the heck out of something. I 'm running mine with a straight spring just so it will give a little.[/QUOTE]

Okay, thanks very much. I'll check 'em out.

Sbroadus 04-02-2012 08:45 PM

Sorry it took so long to post my findings. I tried grounding the antenna mount and it didn't help. I opened the back door enough to get it off the latch and put the weight on the hinges and that didn't help either. The farther I opened the door the better the SWR. I took the top off and as I suspected down went the SWR so question answered. It's reflecting off the top unfortunately.

JokerAndThief 04-04-2012 11:21 PM

I run multiple radios in my Jeep (Amateur band HF and VHF). One of the cardinal rules for good antenna efficiency/radiation is the notion of having a ground plane. On a vehicle the ground plane could be any horizontal piece of metal which causes antenna radiation to reflect upward, rather than a 360 degree sphere you'd get with a vertical antenna.

Your SWR readings are probably the result of a poor ground plane rather than grounding. Opening your tailgate changes the ground plane loading of your antenna, causing it to radiate more efficiently. If you're going to use a coil antenna (Hamstick) mount it towards the front, or on the side opposite the Jeep radio antenna. You'll get a better ground plane mounting close to the center of the metal on the Jeep.

Sbroadus 04-08-2012 12:37 PM

So if I understand correctly. I could possibly get a better SWR by mounting the antenna to the top of the tire carrier as opposed to the side?

dpbergen 04-08-2012 02:16 PM

2m/440 ham antenna mounting on jeep jk
 
I am interested in what you learn. I have a 2010 Rubicon and have been installing cb and ham (dual band 2m/440) in it. I initially tried the Terraflex bracket, mounting both the cb and ham antennas in those two holes, no more than about 2" apart (local ham shack said 'that should be fine').

With the ham antenna cable disconnected, I was getting cb swr readings pushing 10:1 (cb antenna was a firestick 3'). I realized the local ham shack didn't know what they were talking about, and that the ham antenna was way too close to the cb antenna. I then resorted to Coolkit's 4' firestick antenna/cable combo with bracket to mount the cb antenna in the JK's license plate shroud. I recommend this, it gets the antenna away from the body of the Jeep and I have swr's in the 1.2 to 1.4 range depending on what channel I check it on.

Back to the ham antenna (Diamond NR770HB / UHF mount, 40" high) - it's half-wave, so no need for a counterpoise / ground plane. In fact in all my swr measurements, swr didn't change whether a good ground was hooked up to the base of the antenna or not (Jeep's rear door doesn't ground too well). So, a solid electrical ground seems somewhat optional from an swr reading perspective. But, with the spare tire on and the back gate closed, my swr reading on the ham was around 2.5+. Just by removing the spare tire, it dropped down to around 1.4. Leaving the tire in place and just opening the door, also improved swr to around 1.4.

I then took some scrap steel plate and temporarily mounted the ham antenna about 45 degrees off of the right rear corner of the plastic Jeep bumper. It was probably an inch away from the edge of the bumper. SWR read around 1.1. (This was with no electrical ground). I'm concluding that I need to get the antenna away from the body of the Jeep, as best I can. I also have read that you want your antenna as high as possible off of the ground, and above the roof line (won't happen). Roof mount is not an option since I garage the Jeep, and it's got a 2.5" lift to-boot.

Next step is to jury-rig a temporary method to mount the antenna on the rear face of the removable top, to the right of the popup window, as high as I can get it and still not hit the garage door. If I can get it a good 1.5-2" away from the body with a good bracket, this might be the best compromise.

If anybody has suggestions, please let me know!!!
Thanks
Doug
Alpine, CA (San Diego County)

Maro35089 04-09-2012 09:39 AM

Ok my mistake my SWR is at or just above 1:1. with my antenna mounted on the tire carrier i am getting way better range then i did when it was mounted on the bumper. Mounting it on the tire carrier is one of the best place to mount it other then mounting it on the body somewhere. that is what everyone i have talked to has said. the only thing you have to keep an eye on is getting a good ground on the mount. an extra wire might help. with my antenna mounted on the tire carrier i am getting a 4 mile range on the low end. my buddy had his antenna mounted to his bumper so it might be a little better ill have to test that out. but for sure 4 miles and i could still hear him and it sounded ok.

mavrick 04-09-2012 02:39 PM

do you have any pics of where you connected the ground to and from?
I can't seem to find a place on the jeep 4door where to ground the wire without drilling any holes or sanding down paint.

Maro35089 04-10-2012 12:20 PM

I was looking for the same thing but I had a good ground with out and extra ground. See if you can splice into the ground for the 3rd brake light. That should be a live ground.

182250x 04-10-2012 01:29 PM

Curious to know is you have, or heard of any one running HF/VHF 100 watts have had any RF interference to the onboard electronics such as the computer, radio, etc. in the Wrangler Unlimited Sport

Chunks 04-10-2012 01:45 PM

Quote:

Originally Posted by Maro35089 (Post 2236514)
Ok my mistake my SWR is at or just above 1:1. with my antenna mounted on the tire carrier i am getting way better range then i did when it was mounted on the bumper. Mounting it on the tire carrier is one of the best place to mount it other then mounting it on the body somewhere. that is what everyone i have talked to has said. the only thing you have to keep an eye on is getting a good ground on the mount. an extra wire might help. with my antenna mounted on the tire carrier i am getting a 4 mile range on the low end. my buddy had his antenna mounted to his bumper so it might be a little better ill have to test that out. but for sure 4 miles and i could still hear him and it sounded ok.

The worst place to mount any mobile antenna is down low either on the bumper or trailer hitch as ground losses greatly reduce the performance. Mounting the antenna on the tire carrier is better but the optimum location for any mobile antenna is up high on the middle of the roof. Of course for most, this is not practical.

Regards,
Jim N9WW

sparky 04-10-2012 02:39 PM

Quote:

Originally Posted by Maro35089 (Post 2241464)
I was looking for the same thing but I had a good ground with out and extra ground. See if you can splice into the ground for the 3rd brake light. That should be a live ground.

Not a good choice. That's a rubbing contact, and it will work for DC, it is not a good RF connection. Hardwire your antenna ground.

1822 - There is no interference.

Rooster76 04-11-2012 09:16 AM

My take after reading 28 pages on JK forum
 
I don't claim to be an expert but I have spent a lot of time doing research lately and this is what I have come up with.
  • The length of the coax cable is important in top loaded firestik's (18 feet (5.5 meters) )Frequently Asked Questions
  • It's best if 1/3 of the antenna is over the roof line, especially with hard tops that can block the signal.
  • grounding is super important. The tub being better than just the tail gate.
Quote:

Originally Posted by Sbroadus (Post 2233574)
So if I understand correctly. I could possibly get a better SWR by mounting the antenna to the top of the tire carrier as opposed to the side?

There is a lot of interference when mounting the antenna on the tire mount between the glass and rim. It is better to have the mount up higher like useing the ARIZONA ROCKY ROAD ANTENNA MOUNTS FOR JEEP WRANGLER, UNLIMITED AND LIBERTYmount option. I have also seen people mount to the right where the 3rd light is on the back side.
http://www.arizonarockyroad.com/imag...84558-0003.jpg

JokerAndThief 04-11-2012 05:10 PM

It's a question of both how high the antenna is, and the amount of steel (auto body) underneath it. The best place to mount on a Wrangler would be the middle of the hood. Alternately, mounting it on the side front will give you better radiation (and SWR) than mounting on the back. (There's a reason the AM/FM antenna is mounted where it's at.)

Would also second the previous remark about making sure you have a solid chassis ground for the antenna. Most antennas ground through the mounting bracket. If you've mounted the antenna bracket on something semi or non-conductive, run a separate ground wire to the chassis...

Regards

JokerAndThief 04-11-2012 05:14 PM

Quote:

Originally Posted by 182250x (Post 2241692)
Curious to know is you have, or heard of any one running HF/VHF 100 watts have had any RF interference to the onboard electronics such as the computer, radio, etc. in the Wrangler Unlimited Sport

I run 100 watts HF on my Jeep through a 103" whip (and a beefy antenna tuner). No interference problems with engine electronics, no sure about AM/FM reception as I don't run HF/AM/FM at the same time.

JokerAndThief 04-11-2012 05:16 PM

Quote:

Originally Posted by Remus_Redbone (Post 2148313)
I'm catching' on now. Yep, 103' would be more like a double wave dipole.....

Double-wave dipole? Like a Yagi?

sparky 04-16-2012 10:47 AM

Yagi is not a douple wave dipole.
Yagi's are directional antenna's using a driven element (generally a 1/2 wave dipole), and passive elements. A reflector behind the drive element, one or more directors in front of the drive element. Most common configuration is three elements, one of each. There are models with just two; driven and director, and others with many directors in front, sometimes twelve or more. The are just for VHF/UHF work, HF usuallt stops at four due to the sizes involved.

Double wave dipoles (co-linear antennas) are virtically mounted, again VHF or UHF because of size.


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