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-   -   CB with VERY high swr confused (http://www.wranglerforum.com/f274/cb-with-very-high-swr-confused-81354.html)

sssnarl 02-21-2011 04:26 PM

CB with VERY high swr confused
 
Hello all!

I recently installed a uniden 520xl pro with a 4' firestick II antennae. No matter what I do I can not get the swr to an acceptable range. I have checked the connections and all seem to be ok no shorts or anything. the cable is only 8' long should I have gotten the 18' length?

Thanks for any help :-)

KA3PIT 02-21-2011 05:05 PM

I would get the 18 my self,If you go to radio shack they have coax with the ends on it and it seems to work great.Check and make sure you got a good ant ground ,make sure your not pinching the coax also.hope this helps

Rogerg 02-21-2011 05:18 PM

Quote:

Originally Posted by sssnarl (Post 1071432)
Hello all!

I recently installed a uniden 520xl pro with a 4' firestick II antennae. No matter what I do I can not get the swr to an acceptable range. I have checked the connections and all seem to be ok no shorts or anything. the cable is only 8' long should I have gotten the 18' length?

Thanks for any help :-)

Is your antenna tunable?When i first installed my CB i got a firestick where there are no adjustment on the tip.I had to return it and get one that does.

captblack 02-21-2011 06:58 PM

Check your cables, including the connectors. Sometimes high SWR is a direct short between your shield and the center coax.

I would also get the 18' cable - be careful to roll up the extra loosely with no tight bends.

tuff2010 02-21-2011 09:00 PM

Coax explained.........



The length of the coax is determined by the length of the radio wave and the frequency of our radio signal. A full cb radio wave length is 36 feet, so ˝ a wavelength is 18 foot. The cb radio signal is positive for ˝ of the wavelength and negative for the other ˝. At the ˝ wavelength there is what is called a zero voltage point. This is where the signal is changing from a positive to negative or negative to a positive. The zero voltage point is at the half wavelength on every signal sent and received, this doesn’t change. The zero voltage point is where you want your coax to hook up the antenna. This is how the cb shops came up with the 18 foot length of coax. A lot of cb radio shops will tell you that you need to run an 18 foot long coax. Well I’m not a cb technician, but I can tell you that they are not telling you the whole truth.
How do you correctly determine the coax length?
Multiply the wave length by the velocity factor of the type of coax that you are using. This will give you the proper coax length where any excess standing waves (SWRs) are visible to the SWR meter. This way you can have your antenna properly adjusted, and your cb working like it should.
What is a velocity factor?
The velocity factor is a term for how fast your signal moves through your coax. Your radio signal moves through the air at somewhere around the speed of light, but it doesn’t go through your coax at that speed. The velocity factor causes the signal to move through the coax much slower, which puts the length of coax needed to equal a ˝ wavelength less than then 18 foot. The velocity factor needs to be accounted for when determining the length of your coax.
How do I find out what my velocity factor is?
The manufacturers will tell you the velocity factor. The velocity factor is known as the "correction factor". The perfect velocity factor for a coax is a 1.0, but there is no perfect coax. The velocity factors of Belden coax cables used by most cb shops are:

RG-58 velocity factor of .66 RG-58/U (foam) velocity factor of .79

RG-8A/U velocity factor of .66 RG-8/U (foam) velocity factor of .80

RG-213/U velocity factor of .66 9913 velocity factor of .84

By using this information you can find out what length of coax you really need. If you are using a mini 8 coax with the velocity factor of .66 you would need a coax of 11.88 feet long (142 and ˝ inches). This is how got that length: 1/2 a wavelength (18 feet) x the velocity factor (.66) 18 x .66 = 11.88

So when you have a cb shop telling you to use an 18 foot coax, ask them WHY. Now you know the truth on coax lengths. You can get this and other information from the ARRL Antenna Handbook

Hilldweller 02-22-2011 06:08 AM

You should be able to tune your antenna to an acceptable level even with that coax.

Did you ground the mount? Run a length of 10-gauge wire from the mount to a good ground on the frame, check the coax for shorts to the ground (you want none on the center), and tune the stick again.

I prefer the Firefly for Jeeps or the Wilson Silverload "Flex" --- you'll break the Firestick.

The Wilson product also has a ground dongle and instructions if you can't mitigate high SWR.

And don't loop your extra coax at all. Run zigzags.

jeffk42 02-22-2011 06:20 AM

Quote:

Originally Posted by Hilldweller (Post 1073135)
I prefer the Firefly for Jeeps or the Wilson Silverload "Flex" --- you'll break the Firestick.

How? I just installed my 4' Firestik II yesterday. Is there something I need to look out for (other than low ceilings, obviously :) )?

Hilldweller 02-22-2011 09:08 AM

Quote:

Originally Posted by jeffk42 (Post 1073141)
How? I just installed my 4' Firestik II yesterday. Is there something I need to look out for (other than low ceilings, obviously :) )?

Tree branches are evil and eat fiberglass antennas. I've even snapped Fireflies; that's why I'm running the Wilson Flex now; it can bend 180 degrees without complaint.

Peepers 02-22-2011 09:12 AM

8ft coax on a JK? I have an 18ft on my TJ and used the whole thing!

jeffk42 02-22-2011 09:13 AM

Quote:

Originally Posted by Hilldweller (Post 1073296)
Tree branches are evil and eat fiberglass antennas. I've even snapped Fireflies; that's why I'm running the Wilson Flex now; it can bend 180 degrees without complaint.

Hmm... well I just signed up for some trail riding on Saturday. Fingers crossed! :redface:

sparky 02-22-2011 02:54 PM

sssnarl

Where is your antenna mounted and does it have a good ground connection.

tuff2010

Yes, except if you are using a tuned antenna, it does not matter what length coax you are using. It does not have to be a 1/4 wave multiple.

sssnarl 02-22-2011 03:52 PM

Thanks for the replies!

I have it mounted to a 1" strip of HEAVY steel that I bent the last bit at an 90 then bolted it to the aluminum tire carrier. I get almost the same amount of swr with or without the antennae attached. I will try to run an additional ground to the tailgate electrical ground, where would be a good place to ground the mount? anywhere on the piece of steel?

I ran the cable through the roll cage from the tailgate grommet (that is why I got the solder fire ring as it was able to be put through the little holes the soldered at the end.


Thanks again!

Hilldweller 02-22-2011 06:14 PM

Do you have continuity from terminus to terminus? It sounds like you have a bad coax...

seadog 02-22-2011 09:05 PM

Aluminum is NOT a good ground for an antenna. Ground it to steel. Also, set your SWR for the primary channel you will using. I know that the book, tells you center channel, but that is a generic statement. In FL, that seems to be ch 12. Might be different where you are. When you tune it to primary, you are good for about 5 channels up and 5 channels down. Then you start to have roll-off.

KSCRUDE 02-22-2011 09:42 PM

Yes try a Wilson flex. I have tuned at least over 100 antennas in my day. Wilson is hard to beat. All I run on my semis, and some k40s on pickups. And yes you Ned 18 foot of rg 58 I think it is. And a single will usually out perform duals as a rule. You need to place duels at least 8 to 9 feet apart and this is hard to do on smaller vehicles. Every vehicle is different but it can be done. I have put as much as three sets or more on some befor I get it right. Some semis I have I have a duel setup but can only run 1 as they will not tune n cophase no mater what I do. I just use one, but run 2 for the look. Just use the one with the best swr, and sometimes that works great. Most cb nuts only run one as one usually works better. And one is always easier to tune. Good luck.

sparky 02-23-2011 09:46 AM

Aluminum is fine for the mount, it's just as conductive as copper, but you need to get your mount grounded to the body/frame as well.

If your SWR is the same with and without the antenna attached, make sure your antenna connection to the mount is good. It should be clean and tight.

jeffk42 02-23-2011 10:03 AM

I have a tangentially related grounding question...

I installed my spare tire carrier antenna mount and ran the coax, but I never grounded anything. All the same, after tuning the antenna my SWR meter reads just a fraction of a hair under 1.2 at CH20.

So, should I just leave well enough alone? Or is there a reason why I'd still want to make sure it's grounded properly?

sssnarl 03-15-2011 02:10 PM

Ok I know its been a while but life got in the way....

I replaced the connector at the radio end of the antennae wire and the swr problem is fixed! I did not have to ground the mounting bracket on the tire bracket.

Thanks so much for all the help!

Hilldweller 03-15-2011 02:47 PM

Quote:

Originally Posted by jeffk42 (Post 1076017)
I have a tangentially related grounding question...

I installed my spare tire carrier antenna mount and ran the coax, but I never grounded anything. All the same, after tuning the antenna my SWR meter reads just a fraction of a hair under 1.2 at CH20.

So, should I just leave well enough alone? Or is there a reason why I'd still want to make sure it's grounded properly?

hells yes; leave it alone.
That's a great reading.

BTW, you get better SWR readings on a higher mount with more antenna above the roof. My mount, down by the license plate, is great for an OE-appearing mount but not very good from an RF point of view.

jk'n 03-15-2011 03:54 PM

Just for the sake of information, the Firestick is not resonate at 52 ohms so it creates a slight matching problem from feedline to antenna. The 18 foot feed, which is sold with the firestick is the length of feedline required to create a match at the antenna connector of the radio to match the radio to the feedline. All appears well when SWR is measured at the radio but there is still a slight mismatch at the antenna if you were to measure it there. This is one way to "fool" the radio into thinking that it is connected to a perfect antenna. The other way would be to use an antenna that is matched to the feedline and then the feed can be any length. A quarter wave whip is an example of a better matched antenna to feedline connection. That feedline can be any length.

anotherjarhead 06-14-2011 10:11 AM

Breaker! Breaker
 
I did not make a post about my problem because someone else already posted the same problem. HIGH SWR readings. I read every post and tried many including the idea of adding an extra grounding wire to the roll cage none:banghead: of these ideas helped. Finally i found a post that helped. Some of the posts were extremely technical but the post that helped me was not real high tech. Remember K.I.S.S. (Keep It Simple Stupid). After reading this post and following a link provided I found out how true K.I.S.S. fit my situation. :facepalm:
I have had many radios over the years so when I saw the diagram I imediately saw I had put my spacer in the wrong position. This also made me go back and check my connections the one going to the radioo was loose. Now when I key the mike if your not watching you'll miss the needle movment (just a hair off the 1)
It may not help you but here are a few links our friend provided.:)

Hi-SWR Causes
Jeep Installations
Testing Continuity -- 1996 Firestik&#174 Antenna Company

pacu44 09-17-2013 08:30 PM

Quote:

Originally Posted by anotherjarhead (Post 1304953)
I did not make a post about my problem because someone else already posted the same problem. HIGH SWR readings. I read every post and tried many including the idea of adding an extra grounding wire to the roll cage none:banghead: of these ideas helped. Finally i found a post that helped. Some of the posts were extremely technical but the post that helped me was not real high tech. Remember K.I.S.S. (Keep It Simple Stupid). After reading this post and following a link provided I found out how true K.I.S.S. fit my situation. :facepalm:
I have had many radios over the years so when I saw the diagram I imediately saw I had put my spacer in the wrong position. This also made me go back and check my connections the one going to the radioo was loose. Now when I key the mike if your not watching you'll miss the needle movment (just a hair off the 1)
It may not help you but here are a few links our friend provided.:)

Hi-SWR Causes
Jeep Installations
Testing Continuity -- 1996 Firestik® Antenna Company

Those links above helped me fix my problems... Thanks anotherjarhead...

check the antenna mount, make sure connections are tight and (my big one) no hard/pinched right angle...

Channel 1 @1.75 Channel 40 2.75... I am good enough as I only use channels 6, 11, 16, 19 and 21....


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