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cmoores47
02-22-2015, 03:49 PM
Hey All,
Need some help on getting my CB up and running. I mounted the Firestik II in first pic, and could only get a 3.5 on the SWR meter. Then I ran an long ground wire right to the battery negative post and get a 1.8 on the SWR meter. I removed the mount and am now looking for another location. Anyone have a similar experience? Thank you for your help!
Mudderoy
02-22-2015, 07:55 PM
I'd recommend either trying another antenna, another antenna mount, or different coax.

Remember everything is 50 ohm so make sure you're using 50 ohm coax. TV coax is 75 ohm.

An easy way to check the coax all the way to the antenna mount is to connect up a dummy load. You should have a flat SWR, if you don't then you know your problem is with the coax, or how the mount is installed.

I wouldn't run the ground to the battery. I would run it to the body somewhere close to the antenna mount. I doubt you have a ground problem though.

More than likely the antenna has a problem, or the coax. I'm leaning towards the coax issue.

Amazon.com: OPEK Cb Ham Radio Antenna 5 watt Dry Dummy Load 50 OHM: Electronics@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41WadzWqwHL.@@AMEPARAM@@41WadzWqwHL
OldFaurt
02-22-2015, 09:05 PM
Hey All,
Need some help on getting my CB up and running. I mounted the Firestik II in first pic, and could only get a 3.5 on the SWR meter. Then I ran an long ground wire right to the battery negative post and get a 1.8 on the SWR meter. I removed the mount and am now looking for another location. Anyone have a similar experience? Thank you for your help!

Part of your problem is almost half of your antenna is too close to the body and therefore coupling to the body effectively detuning your antenna! The lower part of your antenna is too close to the ground plane (body of the jeep).
If you could mount the base of that antenna mount closer to the roof, you will find you get a better match.

The reason your SWRs went down with the cable was your body was higher resistance than the cable and the cable was not close to the antenna except at the feed point of the antenna.

If you have a roof rack, try c-clamping the base to that and see what happens!
slvmart
02-23-2015, 04:24 AM
I have my Antenna mounted similar to cmoores47. But I used a Firestick no ground pane antenna. They have a yellow band around the base. I've had no issues with the SWR.
Mudderoy
02-23-2015, 06:56 AM
I have my Antenna mounted similar to cmoores47. But I used a Firestick no ground pane antenna. They have a yellow band around the base. I've had no issues with the SWR.

Huh? No ground plane? So it's a half wave antenna? Like what you'd use on a fiberglass body vehicle?
cmoores47
02-23-2015, 08:01 AM
Part of your problem is almost half of your antenna is too close to the body and therefore coupling to the body effectively detuning your antenna! The lower part of your antenna is too close to the ground plane (body of the jeep).
If you could mount the base of that antenna mount closer to the roof, you will find you get a better match.

The reason your SWRs went down with the cable was your body was higher resistance than the cable and the cable was not close to the antenna except at the feed point of the antenna.

If you have a roof rack, try c-clamping the base to that and see what happens!

Great info! I installed a roof rack yesterday I will give it a try.
thanks,
prerunner1982
02-23-2015, 11:10 AM
Huh? No ground plane? So it's a half wave antenna? Like what you'd use on a fiberglass body vehicle?

Got one on the boat.... but think the signal would be better with a normal CB antenna for the Jeep.
prerunner1982
02-23-2015, 11:21 AM
You might look at doing a fender lip mount on the driver's side. Would get it away from the body, might need to run a ground strap from the fender to the fire wall to help tie it in and make sure you have an adequate ground plane.
OldFaurt
02-23-2015, 07:46 PM
I have my Antenna mounted similar to cmoores47. But I used a Firestick no ground pane antenna. They have a yellow band around the base. I've had no issues with the SWR.

Helical wound 5/8 wave length?
Those are great for fiberglass boats, RVs & cars as you say, they do not rely upon the body for it's ground plane. Making tuning for resonance MUCH easier!
OldFaurt
02-23-2015, 08:03 PM
You might look at doing a fender lip mount on the driver's side. Would get it away from the body, might need to run a ground strap from the fender to the fire wall to help tie it in and make sure you have an adequate ground plane.

When you are running coax, you expect the coax to act as the return for the antenna. If it does not, then the shield on the coax become another driven element. Check your cable fitting to see if they are rebuildable, if so, that the braid is properly terminated. If not, your cable will not be 50 ohm resonant & will be very lossy. It will also make for a noisy transmitted and received signals & will give you wildly erratic SWR. With RF energy, Balance is everything!

Also, make sure the ground at the radio is very good
slvmart
02-24-2015, 03:41 AM
Here's the antenna and yes, they are used primarily on boats and RV's where you are typically dealing with a fiberglass body.

Amazon.com: FireStik FG4648-B Four foot No-ground plane CB antenna kit (Black): Electronics@@AMEPARAM@@http://ecx.images-amazon.com/images/I/21neB8mNanL.@@AMEPARAM@@21neB8mNanL

You can go to Firestik for antenna design and theory : http://www.firestik.com/ If that is your concern.
Mudderoy
02-24-2015, 04:11 AM
So I thought it was a bit strange you guys were saying these antennas didn't need a RF ground.

Looking at the Firestik website it appears to me they all need a ground plane unless you use their "no-ground-plane cb antenna kit"

So unless he is installing a NGP kit Firestik I believe he's going to have to be worried about RF ground.
slvmart
02-24-2015, 05:27 PM
Note that the Coax comes as part of the kit from Amazon.
OldFaurt
02-24-2015, 10:02 PM
So I thought it was a bit strange you guys were saying these antennas didn't need a RF ground.

Looking at the Firestik website it appears to me they all need a ground plane unless you use their "no-ground-plane cb antenna kit"

So unless he is installing a NGP kit Firestik I believe he's going to have to be worried about RF ground.

They still need the coax to be properly terminated, but a 5/8 wave is designed so there is no need for a tuned counterpoise (ground plane). with a 1/4 wave, you need a balanced ground plane of like resonance or the energy is reflected back at the radio.
this PDF Antenna book can help explain them! (http://files.radioscanner.ru/files/download/file311/practical_antenna_design.pdf)
Mudderoy
02-24-2015, 11:32 PM
Oh before I forget again.... Check out this guy for some really nice and beefy antenna mounts!

https://breedlovemounts.com/Home_Page.php

https://breedlovemounts.com/images/2ee52000d5d6ab94326623e0d22ec19a_fi5q.jpg
cmoores47
02-28-2015, 10:56 AM
7096Hey All,
Well I got it mounted thanks to you all. I think I can do some serious weed whacking with it though. I don't like the cb mounted between the visors so I am looking for a new location.

Amazon.com: Firestik (FS-3BK) Black 3' 650W Tunable Tip CB Antenna: Automotive@@AMEPARAM@@http://ecx.images-amazon.com/images/I/316vSBXWYrL.@@AMEPARAM@@316vSBXWYrL