|11-18-2012 12:11 PM|
Grounding the antenna to the battery won't do much good. The antenna wants an RF ground, not a DC (voltage) ground. The shorter the RF ground connection, the better.
Using a license plate holder for a 108" whip might place too much stress on the mount. It looks like it only has one bolt holding it on. Hopefully, that bolt is designed to go into the sheet metal of the rear fender. I'd be afraid to use that small mount with a 3 or 4 foot CB antenna. The first time you hit a branch or other overhead obstruction, that one bolt might tear loose. I think I'd drill at least 2 more holes in the mount and use some 5/16" or 3/8" sheet metal screws. That will help with both the physical strength of the mount and the RF grounding/bonding.
Whatever mount you use, and location, ensure you have a good, clean, metal to metal connection. On the mount you listed, that should be fine. It is unpainted, the bolt holding it on hopefully goes into the fender sheet metal, which should also give you a good metal to metal connection.
|11-18-2012 10:30 AM|
Coax for a CB shouldn't really matter, so long as it is purchased from a quality source. RG58 is gonna be what most probably use, RG8 is another decent option. I run RG8X (mini 8) for my 144mhz rig.
18' has been said to be the magic number, although I can find no science to support cable length matters at all for tuning purposes unless a NGP antenna is used. 18' is common and usually gives enough for any Jeep install, so it is good for real reasons.
Antennas on Jeeps are comprimises. The recommended place for vehicle use onroad is pass rear bumper, as the typical vehicle will give an RF pattern favoring the drivers front, or where oncoming traffic comes from. Truth of the matter, if you get good swr you should be good to go. Best electrical placement would be the hood, a bit unrealistic with a 102 whip. Front bumper would be better than rear, but still not as good as hood or cowl.
As far as radio, http://www.wranglerforum.com/f40/bas...de-184216.html should give some insight.
If you are planning on going trail riding, be careful using a 102 whip. It will beat your Jeep and any friends who dare too close pretty intensely.
Oh, I would ground to the frame and make sure your primary ground strap is good. Connecting things to the neg batt terminal can cause big trouble if the primary strap has a problem. If you want to ground to the battery, either fuse the line or connect at the common ground. Be wary of noisy spots. I ran my mount to frame, then ran a strap from that spot to the batt neg. It is sort of like a safety gate for a ground, but leaves the potential for a loop.
|11-18-2012 08:00 AM|
Instead of starting a new thread since this is dealing essentially with the same topic..... I want to install a 103 in whip on a license plate holder (http://www.cooltechllc.com/jeep/jk_ultramount.shtml) on top of a spring (6in? to make it a true 1/4) then ground it to the battery to make sure of a solid ground connection. Questions would be what is the best coax to purchase for a CB application. I understand there is great variability with the quality of copper coax, its shielding rating ect. As I understand the above discussion, it really does not matter (for a CB installation) the length of coax. As to position is there truly a better position than another with the 103in whip? And if so, would the left rear corner be an acceptable compromise for said application. I understand that personal preference is a huge factor in what brand of cb to buy, but any suggestions on a small compact unit that has what is really needed in a radio that would fit above the rear-view mirror on a 2013 JK? Comments, suggestions?
|11-10-2012 11:55 PM|
|Fireslayer||Any one in SoCal want to buy a new 4' Firestik Firefly?|
|11-10-2012 06:02 PM|
|sport454||Don't confuse ground and ground plane. Get the silver load antenna and your equipment will be happy. If you absolutely want to have your antenna where it is. I have set up hundreds of ATV's that have non existent ground plane surfaces using the silver load and they perform good and check out at below 1.6 with a 42 to 54 ohm load using a MFJ Antenna Analyzer.|
|11-09-2012 11:10 PM|
You are mounted to the tailgate and you are getting 1.6? You are one lucky dude! I would kill to have 1.6.
I mounted to a terraflex spare tire bracket, and I've had nothing but problems.
I scraped and ground away paint and powder coating. I ran a separate 10ga. wire to the bracket from the tub AND the tie down bracket inside the rear tailgate. According to my multimeter, I have .1 not only at the bracket but at the coax coupling. I was still only getting my swr to 2.75 with a 3' firestik firefly.
I called the firestik tech and he told me that I needed to try jumper cables from the frame to the coax. If I didn't see improvement, it wasn't my ground, it was my antenna. I swapped for a 4' firefly. I was able to get the swr down to 2.25ish. And that is the best that I can get from the spare tire mount. I hate having a 4' antenna and it pisses me off even more that I can't get my swr below 2.
I have a windshield light bar so I stuck a flimsy "L" bracket to the light bar and ran my coax to it. I was able to get 1.2 I really don't like the antenna there, but I think it is time to rethink my mounting location.
If I knew how to run a ground strap, I would try that just for shats and gaggles before relocating my antenna. I've only seen photos of one ground strap, and it looked unclean.
Anybody have a good way to run a ground strap? I would like to see how you did it.
|11-08-2012 11:02 AM|
Good post, and it's a subject that is rarely, if ever discussed, during CB installs. Without being aware of this effect it can cause all sort of difficulty during a setup.
So when you are trying to tune that antenna, do it the same way you operate. Tailgate closed, doors closed, driver in seat, top in the most used position, and nobody standing too close to the vehicle.
|11-07-2012 06:45 PM|
Those who have an antenna mounted on the tire carrier and notice the VSWR change when the carrier is opened (lowest VSWR) or closed (highest VSWR) are seeing, first hand, the Near Field Effect. Look it up and choose your source carefully. Scientific papers are the best source, antenna manufacturers are the worst. Wiki isn't very good either.
The short story is that objects surrounding the antenna, up to one wavelength out or 36 feet in the case of CB will affect the way the antenna operates. These objects do not need to be conductive. They distort the electric field and therefore the loading of the antenna. The increase in VSWR thus caused will not respond to antenna tuning. This is because it does not change the resonant frequency of the antenna. As you open and close the tire carrier and monitor the resonant frequency, you will see the depth of the antenna resonance change as the VSWR changes, but the primary dip point will not.
The closer the interfering items are, the more the effect will be. Things like tires, tops, tubs, jacks & other antennas will all have an effect. As mentioned in other posts the higher your antenna, the less these effects will interfere.
Prattle about grounds, ground planes and bonding are another issue and not related to this effect.
As in real estate, the primary concern is location (of the antenna). Some of the best installations with regard to this subject, have the antenna installed on either front fender, a foot or more in front of the windshield. If you can tolerate that position and your wheeling style doesn't kill it, then consider it.
Most of us who understand VSWR and its minor effects (within reason) settle for a rear mount as high as possible and remain happy.
|11-07-2012 04:23 AM|
If you are having swr problems with vehicles that have a crappy ground plane configuration then do yourself a favor and order or find a truck stop that sells the Wilson brand silver load antennas. These antennas have a ground wire at the base that can be hooked to ground if you are having issues.
I have worked on and repaired base and mobile CB equipment for over 20 years and I run 5ft silver loads on my Duramax with great performance and anytime I get a Jeep, tube buggy or atv that's giving me fits the silver load has saved the day.
These are fiberglass antennas from 2ft to 5ft and have the adjustable tips. They have the large type that's good for 1000 watts and a smaller diameter "flex" series that's good for 200 watts.
Here some information
They can be ordered from www.copper.com just type silverload in the search. Try a truck stop first shipping from there is pretty high for an antenna.
Hope this helps.
|11-07-2012 03:56 AM|
SWR. Important, but with limits...
I have spent a lot of time, and used professionals to help me, and teach me.
I am not a pro by any means, but I have gained some knowledge over the years playing with CB's.
First of all. It's strange when I hear people talking about SWR under 1:1..
Some are actually mistaken, and all respect for that. It's not common knowledge knowing how to adjust SWR...! But it is just plain impossible to get that result (at least on a car). Period... The fact is, there are other things that are important too, like the shape of your car, weather, cables, watts, ground plane ++. But we tend to get hooked on getting a low SWR. And yes, it's a good thing to keep it low, but don't get crazy...
I will not go into too many details. There are other threads for that, but let me say it like this. If you place your antenna on the rear part of a car, it will normally have a better range forward (if unobstructed), as it uses the shape and thickness of the metal in your car to transmit.
And if the antenna is in the front part, more range backwards. Corner placement has the same functionality.. Opposite maximized range (depending on the frame, line of sight and body shape). A friend connected his radio to a barb wire fence, and it worked too. No antenna! But I guess his SWR was way too high for long term use...
Most cars have a lot of options regarding placement of the antenna.
JK..., not so much.... And if you get an SWR below 2 at your choice of location, you are well on your way, and there is little reason to fight for hours to get it .2 lower... That is unless you have plans other than talking to people that are with you, or at least a few miles away.
If your plan is to make new friends far far away..., and you think this is interesting and fun (like I did), tweak all you want. It might be the last .1 that makes you reach what and where you want. If you want to talk to others close by on the trail/freeway, don't bother.
But make sure your SWR is low enough to NOT cause damage to your CB Radio. You WILL damage your radio if your SWR is too high!
Some say that magic number is 3, some say it's 2.5.
I always stay under 2.1, to make sure I am ok! Other than that, I don't care anymore. My priority is to get the antenna high for a "no obstacle transmit" (Not on a bumber, behind a hardtop and/or other "bad" places)
This is just my opinion, and I am sure some will disagree. That's why we bring these things up in forums. To find solutions for everyone!
And to give and gain knowledge. I am gaining every time I log on a JK forum, and I am smiling every time I find and answer to my question!
As I said, up to you, and your needs.
Have a great evening!
|06-26-2012 11:18 PM|
Antenna 101 - the transmitter sends a signal to the antenna, which is sent to the tip, then radiates out. This radiation of microwaves must then "bounce" off of a large, flat, square, reflective, metallic surface, and from then it propagates into the atmosphere. This piece of metal is a ground plane, or counterpoise, and forms the "2nd half" of your antenna. Without it, the antenna is not matched, and the system is incomplete and will not properly function. Jeeps have little to no ground plane on the rear - there is just nothing there to reflect off of.
"All "FS" antennas are compatible with autos, trucks, vans, motorcycles and ATV's in a single antenna configuration when metallic ground plane is available. Or, they may be used in dual (co-phased) configuration on any vehicle made from any type of material."
Basically your ground plane is varying when you move the relevant location of the antenna to the body of the vehicle (open/close the gate), which is changing the SWR. Unfortunately, it seems Jeeps get worse with it closed than open.
3:1 sounds like a bad ground, or maybe just a nonexistent counterpoise (too low antenna). Height will help, as others said 1/3 above the roof, especially with hard tops. The fiberglass and real glass are more obstructive than a soft top, leading to lost radiation (the waves can't get through - glass doors on microwave ovens and all).
Having said that, I imagine both measurements are right (variance of door open) with the CB shop meter reading likely having a higher degree of accuracy (you read ~2.5, they read ~3).
|06-26-2012 12:43 PM|
|Maro35089||Yea that's a good question. I have the same mount location with no problems. But I am also running a 103' whip so I can't tune the antenna. I am getting a 1.2 or so with my setup|
|06-21-2012 01:33 PM|
Yet another CB tuning SWR meter question!!!
|04-16-2012 11:47 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.
|04-11-2012 06:16 PM|
|04-11-2012 06:14 PM|
|04-11-2012 06:10 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...
|04-11-2012 10:16 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.
|04-10-2012 03:39 PM|
1822 - There is no interference.
|04-10-2012 02:45 PM|
|04-10-2012 02:29 PM|
|182250x||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|
|04-10-2012 01:20 PM|
|Maro35089||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.|
|04-09-2012 03:39 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.
|04-09-2012 10:39 AM|
|Maro35089||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.|
|04-08-2012 03:16 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!!!
Alpine, CA (San Diego County)
|04-08-2012 01:37 PM|
|Sbroadus||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?|
|04-05-2012 12:21 AM|
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.
|04-02-2012 09:45 PM|
|Sbroadus||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.|
|03-18-2012 03:11 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.
|03-16-2012 11:31 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.
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.
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