Strange Antenna Warning.

[BruceJM]

I have a new Cobra 29LX, a new firestick adjustable antenna and all new studs, cable of the right length and such, all mounted to my jeep(yes I know horrible platforms for CB's)

The antenna mount is part of the aftermarket tire carrier and I installed a stainless steel braided ground strap from the tire carrier to the frame rail of the jeep(Very good conductor).

All conductive surfaces are cleaned and free of any kind of coatings. The plastic washer on the stud mount is correctly installed between the top of the stud and the mounting surface(insulating the antenna from ground), leaving the screw on bottom of the stud creating the ground connection

I first tried using the SWR meter on the cb to adjust the antenna and could not get it done. Always 3.0 SWR reading.

Bought a meter from the local truck stop and adjusted it with that. I get around 1.8 SWR and no antenna warning with the meter hooked up to the cb.

When I take the external meter out of the antenna circuit and hook My SWR goes right back to 3.0+ SWR and an antenna warning flashing on the CB. The only thing I have done was to take the external SWR meter out of the loop.

What's going on with this, any ideas.

Thanks in advance, Bruce.

 

[prcguy]

Antennas mounted on tire carriers are notorious for insufficient ground plane and difficulty in matching. As a result the coax ends up being most of the counterpoise for the antenna and RF current will be flowing on it. To prove this attach 9ft of wire to the antenna mount, stretch it out sideways and check the match. I'll bet you can tune it pretty good with little interaction taking the meter in and out.

In the case of your existing setup you can actually tune the length of the coax because its a radiating part of the antenna and when you put a meter with jumper cable in line you change the length and tuning. You might make things better or you might make them worse depending on where the coax length was tuned before adding the meter.

The idea is not to tune your coax or have an antenna that is in any way sensitive to coax length. You probably need more metal around the base of the antenna as a ground plane but it may not be possible to get there with a Jeep, depending on the model. You also can't drive around with 9ft of wire sticking out the back of your car. You can place a 1:1 ferrite choke balun near the antenna or somewhere slightly down the coax to keep RF off the coax and minimize the coax length interaction, then custom tune the antenna with a small value of capacitor at the mount like a 25 to 50pf disc ceramic.

Tuning an antenna this way can achieve a great match and allow the radio to operate but performance will still suffer some due to a squirrely radiation pattern. You can make a very effective RF choke by wrapping about 8 turns of your coax through an FT-240-61 ferrite core which costs about $10. If you have some snap on ferrite beads that will fit over your coax you can put at least several over the coax and slide that up and down the coax to find a sweet spot where the match is better and taking the external SWR meter in and out of circuit will have the least affect. Then install the ferrite core I suggested as it is many times more effective than some snap on beads over the coax.
prcguy

 

[BruceJM]

Excellent reply with consice instruction that I can understand, I really appreciate that and it all makes sense to me now.

Tomorrow I will do the test with a piece of wire to check and see if it is in fact the lack of a ground plane, I'm betting it is.

The tire carrier only has about a 4" metal platform elevated to roof line which serves as the antenna mount. The roof is fiberglas so no help there for a ground plane.

Thanks again and I'll report back with my results.

 

[prcguy]

Aah, sounds like a Jeep Wrangler type. Its been a long time since I've installed a CB antenna on one of those, but I've probably done several dozen or more when I was much younger. The tire carrier mounts were always a PIA but some that got a ball mount on the rear quarter panel and a full lenght 9ft whip tuned up ok.
prcguy

Excellent reply with consice instruction that I can understand, I really appreciate that and it all makes sense to me now.

Tomorrow I will do the test with a piece of wire to check and see if it is in fact the lack of a ground plane, I'm betting it is.

The tire carrier only has about a 4" metal platform elevated to roof line which serves as the antenna mount. The roof is fiberglas so no help there for a ground plane.

Thanks again and I'll report back with my results.

 

[BruceJM]

Yes it is a wrangler.
Hmmm a ball mount you say. I'm not apposed to drilling a hole and mounting a whip antenna to the side quarter panel if it will in fact create a better ground plane for this set up.

 

[Project25_MASTR]

Aah, sounds like a Jeep Wrangler type. Its been a long time since I've installed a CB antenna on one of those, but I've probably done several dozen or more when I was much younger. The tire carrier mounts were always a PIA but some that got a ball mount on the rear quarter panel and a full lenght 9ft whip tuned up ok.

prcguy

I’ve always been fond of hood channel mounting on wranglers. Hell, I even mount there with my XJ when it comes to CB. Of course I use NMO based antennas but that’s besides the point.


Sent from my iPhone using Tapatalk

 

[lmrtek]

Firestick sells a NGP (no ground plane) antenna kit that is made to be used in your situation.

 

[BruceJM]

Firestick sells a NGP (no ground plane) antenna kit that is made to be used in your situation.

Yes I am just now seeing that on their website.

I am after the best performing antena that I can achieve, have said that which of these three different antenna builds would be more effective, not necessarily easiest or cheapest but best performer.

1) The RF choke

2) side mount whip antenna

3) the Firestik NGP antenna

What say you all, I appreciate the shared experience.

Bruce.

 

[fireadioguy]

The ball mount , with the spring ( it is part of the antenna) and the 9 ft whip, will always outperform any of the other option listed. The NGP and the beads will get you a good swr, but the 9ft whip should get you a better swr, and better performance. You won't be "fooling" your radio into seeing 50 ohms, it will be seeing 50 ohms. Ive used 9ft whips on a few cars, and made a few base antennas out them have talked to Europe on stock radios.

 

[prcguy]

A side of hood mounted antenna like a Larson should work and tune ok, I just avoid it due to potential ignition noise, since your right on top of the engine. If people have mounted antennas there and report no ignition noise, then I think its worth considering.
prcguy

 

[BruceJM]

As far as mounting locations, does the 9" whip antenna eliminate the ground plane issue or would I still be limited to where I can mount that antenna or any antenna for that matter.

 

[BruceJM]

Just did the 9' wire experiment from the antenna out across the roof top and got great sir readings on the internal cb swr scale with no antenna warning, so it's safe to assume that prcguy hit the nail on the head, thanks.

 

[JayMojave]

Hello BruceJM: Yeah again what PRCGUY said. Good call.

I run with a bunch of Jeeps and such here in the Mojave Desert. Being asked to look at a few Jeeps CB installs as the SWR was high and getting a SWR warning light come on one jeep. I brought my Antenna Analyzer with me and all my soldering and tools and new coax and PL-259 connectors, to a camp we had last weekend.

While running on the 4 wheel drive runs and all over the place in the El Paso Mountains, everyone could talk to each other with no problems, even when miles apart, even with high SWR on there antenna system. Yeah many use the tire rack and some use a side mounted whip antenna. And these antenna systems have a 3 to 1 or more SWR, but that SWR isn't the end of the world. All the Jeeps radios worked OK. One guy had a Wilson 5000 magnet mount on top of his metal roof and it worked better than all of them.

They also used the VHF Murs Radios and they worked great. Many had hand held cheapie Chinese hand held radios.

Yes the 9" whip will require a ground plane but I've seen these mounted on metal roofs, and the metal over the windshields work pretty well. Good Luck.

Jay in the Great Mojave Desert

 

[BruceJM]

Thanks Jay, but I'm a bit OCD with this kind of stuff, a antenna warning coming up and just knowing that I'm my antenna isn't at optimal performance would bug the crap out of me every time I keyed the mic...Just one of my weird querks.

Bruce.

 

[Project25_MASTR]

A side of hood mounted antenna like a Larson should work and tune ok, I just avoid it due to potential ignition noise, since your right on top of the engine. If people have mounted antennas there and report no ignition noise, then I think its worth considering.
prcguy

In my experience, the alternator is the big issue with Jeeps. That being said, if it's an 01 or newer engine it should be using a distributorless system and ignition noise would be minimal. My 1999 Cherokee has alternator whine but not ignition noise for example.

 

[BruceJM]

Having today off decided to go out and freeze in the garage and relocate my antenna mount to the front of the jeep at hood height.

I mounted a simple 'L' bracket that I had using one of the windshield bracket bolts and that put the base of the antenna right exactly at hood with an excellent ground.

I re-routed the cable and mounted the 4' firestik antenna and I now have right around 1.3 to 1.1 SWR on the cb meter.

I'm onto of a mountain in a rural area of NYS and am about 15 miles from the interstate as the crow flies and I could hear truckers on the highway, all be it very faintly I was receiving pretty well for a down and dirty mount.

I'll see if I like this set up before I go and purchase anything with better reach.

I thank you all very much for the help you have been giving me,
Bruce.