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High SWR on new install

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#1
I installed a CB radio system in my Grand Cherokee and I'm getting high SWR readings, roughly 2.2 on channel 1 and 40. First, some details about my setup.

Radio: Uniden 980SSB
Antenna: 3' Firestick 2 (adjustable)
Coax: 17' Firestik Fire Ring

The Antenna is mounted near the drivers side taillight as shown in the picture. I realize this location is not ideal and that the antenna is a bit short, but I want to see if there is anything I can do to improve the SWR before relocating the mount and or getting a longer antenna. The Coax runs under the carpet and is not coiled at any point. I did however cut about one foot off and soldered the connector on. I’ve read a variety of opinions regarding coax length and there doesn’t seem to be any concrete evidence to support a full 18 feet versus trimmed to the proper length.

Containment: I’ve been checking SWR in an open area using the built in SWR meter. With antenna cap installed I calibrate then check SWR on channels 1 then 40 then adjust. I’ve checked the coax for shorts and none exist. I installed an additional wire from the mount to the chassis to make sure I’m getting good ground.

Side note: I made contact with someone 30 miles away and they reported a strong signal. It’s probably not relevant, but I was surprised and figured I’d mention it.
 

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#2
That is a crappy location for a CB antenna. The vehicle body is going to block the signal to the front and right, especially given the antenna is not much higher than your roof. Your SWR is about as good as can be expected.

If you want best performance, the antenna goes in the center of the roof. Anything else is going to suck in comparison.
 
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#3
High SWR on new instal

I just did two friends installs over. One on a 2006 Silverado Crew Cab and the other on a
2008 Jeep Grand Cherokee both using Firestiks and that new fangled Fire Ring.

Both had SWR readings almost at 3 and couldn't get it down no matter what they did. They checked all the things you did but no good.

Without uninstalling their coax, I took another 18' long piece with spade lugs on the end, unhooked the Fire Ring coax and mounted the antenna with the lugs, screwed on the PL-259 to the back of the radio, didn't touch the antenna tuning and just like that, the SWR dropped to 1.4 on 40 and 1.7 on Ch 1.

That was on the Silverado so, I did the same on the Jeep and, wouldn't you know it, the SWR was just the opposite so, I tuned it lower on 40 as he wanted to talk on the higher channels the most.

So what I did to both was cut off the Fire Ring end, put on some lugs, and installed the coax like the old days and all is well. Both of them are very happy now.

I know some people use Fire Ring systems and have no problem but, these two were not working.
 
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#4
The fire ring was one of my suspicions. One of the these I'm weighing is spending $25 on a new coax and hope that fixes it or spend that same money on a stand alone swr meter and hope that the built in meter in the radio was giving a high reading.

Most likely I'm going to get a new 18' coax with p-259 connectors on both ends and not trim it.
 
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#5
The fire ring was one of my suspicions. One of the these I'm weighing is spending $25 on a new coax and hope that fixes it or spend that same money on a stand alone swr meter and hope that the built in meter in the radio was giving a high reading.

Most likely I'm going to get a new 18' coax with p-259 connectors on both ends and not trim it.
Just cut the Fire Ring part off like I did, crimp or solder lugs on the end and use the same
stud mount. No expense or running new coax.
 

ipfd320

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#6
Firestick Website Link Below---NOTE How the SHOULDER Washer is Placed Into the Bracket on the Image Link--Alot of People who I Know Messed this Up and Got a Hi SWR--Plus Like jonwienke Said There is Alot Against You---The Rack and Jack are Throwing the RF Right Back Into the Antenna--Besides the Metal Body of the Car---Well Check Out The Site it is Pretty Informative---Good Luck

Forgot 1 More Thing----The Tuning Screw Might have to be Cut Down That can be Found Here---
http://firestik.com/Tech_Docs/long-tt.htm

This is the Image Link
FireRing Stud Mount Installation

This is the Website Link
Tech-Docs Index
 
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#7
The vehicle is not blocking the signal and you should consider that a wavelength at CB is about 36ft and a CB antenna a foot or two below the ground plane is not a big deal like it would be on VHF or UHF.

You will actually have the best signal to the front right side of the vehicle where there is the most ground plane. There may be a slight lack of ground plane around 3/4 of the antenna radius causing a difficult match, or it could be the way Firestick terminates their "fire ring"

I would find an antenna analyzer and see exactly where the antenna is resonant, it cold be working fine above or below the CB band and some trimming might fix things, but you don't want to trim anything without knowing more info.




That is a crappy location for a CB antenna. The vehicle body is going to block the signal to the front and right, especially given the antenna is not much higher than your roof. Your SWR is about as good as can be expected.

If you want best performance, the antenna goes in the center of the roof. Anything else is going to suck in comparison.
 
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#8
The vehicle is not blocking the signal and you should consider that a wavelength at CB is about 36ft and a CB antenna a foot or two below the ground plane is not a big deal like it would be on VHF or UHF.
What you're saying would be correct if the OP was running a 102" whip. But not when only a 12-18" of a 3' antenna is above the roofline.

You will actually have the best signal to the front right side of the vehicle where there is the most ground plane.
Not if most of the signal starting off in that direction is reflected upward or horizontally off the vehicle body. If the antenna mount was raised so that the base was at the same height as the roof then you would be correct.
 
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#9
The vehicle is not blocking the signal and you should consider that a wavelength at CB is about 36ft and a CB antenna a foot or two below the ground plane is not a big deal like it would be on VHF or UHF.
What you're saying would be correct if the OP was running a 102" whip. But not when only a 12-18" of a 3' antenna is above the roofline.

You will actually have the best signal to the front right side of the vehicle where there is the most ground plane.
Not if most of the signal starting off in that direction is reflected upward or horizontally off the vehicle body. If the antenna mount was raised so that the base was at the same height as the roof then you would be correct.
 
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#10
Changing the coax cable to a different length and that made the SWR better?? Most likely the coax cable is has now become part of the tuning of the antenna and NOT a transmission line. And you will have lots of loss of signal.

You can take a length of coaxial cable with a short circuit at the far end, and at the correct length your SWR will be one to one. About 18 feet of cable is the length for CB.
 
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#11
RF blockage in this case is more dependent on wavelength not antenna size as the radiated wave is much larger than this particular antenna. If half of a 3ft antenna at 27MHz is below roof line its just a small speed bump to the radiating wave and the resulting pattern will follow the large mass of roof ground plane towards the right front of the vehicle.

Once the OP gets his SWR problem under control maybe he can drive in a circle and let us know what direction has the best signal, and I say it will be towards the front right and it will be very noticeable.

If I win you owe me lunch and if I loose I'll buy. In either case lunch will be served in Southern Kalifornia.



What you're saying would be correct if the OP was running a 102" whip. But not when only a 12-18" of a 3' antenna is above the roofline.



Not if most of the signal starting off in that direction is reflected upward or horizontally off the vehicle body. If the antenna mount was raised so that the base was at the same height as the roof then you would be correct.
 
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#12
I had a similar situation. Except that my antenna is a 5.5' long center loaded 1/4 antenna centered on the roof of my van. I changed my cable from RG58 to RG8X. My SWR would not come down below 2:1. I decided to look into the coax since the antenna is tuned as flat as it can be across the band. I removed some excess I had rolled up, about 3', and reused the PL259. My SWR has become much more acceptable, below 2:1.

Understand that for years I have always experienced the fact that coax length has no effect. But then I must consider what I just experienced. In most cases length didn't appear to be a factor, when dealing with higher frequencies or base station installations. In a mobile installation where coax lengths are shorter, less than 1/2 wavelength (18') for 11M, then the length does have an effect.

The characteristics of coaxial cable are rather unique but predictable. Taking one quarter wavelength of coax of any given frequency, the characteristic (RF) impedance at the feed point is an open, then capacitive, then inductive, then a RF short. Add to that another 1/4 wave and the process reverses, short, inductive, capacitive, open.

When dealing with 11M mobile antennas we are stuck with a less than ideal antenna. That's why you can't get your SWR down. The only way to get past that is to compensate elsewhere. Since we're dealing with a RF short cable then we must deal with the characteristics inherent with it. The simplest solution is to make sure you have 18' or more of coax. Trimming coax is a tedious process and a crap shoot at best.
 
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#14
Thanks for the replies. I'm going to try replacing the fire ring with a p-259 connector. If that doesn't fix it I'll replaced the coax with a new untrimmed 18 foot cable. If that fails, I'll be back...
 
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#15
Interesting....The info on coax albeit correct I have never has 18' of coax in a mobile in 40 + years of playing CB... Not trolling or arguing, just curious.
What is the OP is to do with excess in a small vehicle. Roll it up...bad idea no? unless he is making an rf choke.
Generally as a rule properly mounting, grounding and adjusting an antenna on a mobile works well with no need to run excessive coax. Is this a case of real world correct antenna theory vs learning to live with the shortfalls of practical radio?

Anyway, had to ask. Good luck to thr OP and hope it goes well. :)
 
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#16
The 18' coax length thing is a superstition. Use the shortest practical coax length to get the job done.
 
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#17
Instead of engaging in opinions and theories of amateurs, why not call the professionals at the Firestick Antenna Company and see what the people that MADE the antenna say?

It's a FREE phone call
 
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#18
Links for Firestick are in this thread and I have found there website to be informative.

Going to the source woukd make sense. , Lots of very informed mbrs here but checking all sources is logical.
 
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#19
Not everyone participating in this thread is an amateur. And Firestick's customer service people are unlikely to be professional RF engineers.
 
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#20
I have almost the exact same setup on my van, and I'm also having issues with high SWR, as well as inconsistent SWR. I'll set it so it gives me 1.2 on Ch 19, then I'll check it the next day, and it's up to 2 or even 3:1 somehow. I don't know if I've got a bad cable assembly, or the adjuster screw is somehow not working, but it's annoying. I'd swear there isn't a short anywhere, my tests show no continuity between the conductor and shield on either end. As far as the antenna goes, I can't really run one much bigger, I have to go in and out of parking garages, and I can't have a huge antenna bashing against the ceiling fixtures. I was under the impression that most of the power is radiated from the top of this kind of antenna, and as long as you had ~12-18" above the roof, you should be OK.
 
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