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Old 12-11-2011, 06:10 PM   #1
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Finally got my CB working/SWR resolved

I struggled with SWR issues for quite a while after installing my CB system, and finally got the issue resolved this morning. I thought I'd share the experience here for anyone else who may have similar problems.

I wanted a CB for trail riding with my buddies. I didn't want to spend a whole lot, because it would mainly be just for trail use. I bought a Cobra 19 Ultra III CB from Walmart, and a Firestik KW3 antenna, antenna mount and 10 foot coaxial cable from Radio Shack. All together, I think I had $80 into the system.

The install went pretty easy. I mounted the antenna onto my Body Armor swing out spare carrier. It has a tab specifically made for mounting a CB antenna. I used a wire brush to remove the powder coating from the mounting surface to ensure a good ground for the antenna.

After getting everything hooked up, I pulled out into the driveway to give it a try. I live approximately 4 or 5 miles from the interstate, so I was hoping to be able to communicate with some truckers on I-10. I turned it on, changed to channel 19, and was able to receive, but it was very faint and scratchy. I tried asking for a radio check, and got nothing back. I just figured I was too far away. So I tried again the next time I was on the freeway, and still nothing back. So I decided I needed an SWR tester.

I borrowed an SWR tester from a friend and hooked it up. The SWRs were spiked, off the scale! So i did some troubleshooting, assuming I had a bad ground or a short. I got my multi-meter out, and tested everything I could test. Everything that was supposed to be grounded was grounded, and everything that wasn't, wasn't. All was well in the world of continuity.

I searched this forum and read all the threads relating to SWR and CB issues, and nothing seemed to show me the error of my ways.

My next thought was maybe the coax was too short. Everything I had been reading told my that an 18 foot coax is the optimum length, and I only had 10 feet. Of course, my local Radio Shack didn't have an 18' coax, so I ordered one online. It arrived last night, and got installed this morning.

To make a long story, well, long, that fixed it!! SWRs were high, but they were readable on the scale. After printing out the tuning instructions, I drove out to get away from structures and tuned and trimmed my antenna a few times. I got the SWRs down around 1.3-1.5, and got a "5x5" on my first request for a radio check!

So if you are struggling with high SWR, consider the length of your coax. It makes a difference.

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Old 12-11-2011, 08:18 PM   #2
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Thanks for the information. I am sure it will help more than a few jeepers out there!

Take care,

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Old 12-11-2011, 11:37 PM   #3
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The length of your coax has NOTHING to do with how well your system is tuned. It's a myth. Notice that your SWR, while lower, was still high even after you added the extra coax, and didn't come down until AFTER you adjusted your antenna length. The additional coax masked your high SWR due to the way radio waves propagate in a transmission line.

The ONLY way to tune your system is to adjust your antenna length. SWR will indeed be lowered by changing the coax length in some cases, but low SWR does NOT necessarily mean an antenna system is optimally tuned.

Here's a link explaining more about this...

http://www.stu-offroad.com/misc/myth-1.htm
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Old 12-12-2011, 09:57 AM   #4
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The length of your coax has NOTHING to do with how well your system is tuned. It's a myth. Notice that your SWR, while lower, was still high even after you added the extra coax, and didn't come down until AFTER you adjusted your antenna length. The additional coax masked your high SWR due to the way radio waves propagate in a transmission line.

The ONLY way to tune your system is to adjust your antenna length. SWR will indeed be lowered by changing the coax length in some cases, but low SWR does NOT necessarily mean an antenna system is optimally tuned.

Here's a link explaining more about this...

Exposing the 18' CB Coax Myth
That brings up two questions:

1) If the optimum length of coax is a function of wavelength and cable VF (presumably a value known to the cable manufacturer), are there people out there selling optimum-length coax?

2) Other than SWR, is there any other way to determine when an antenna is "optimally tuned"?

I'm in a location that has relatively little CB traffic, so I don't really have a way to test my setup. SWR is 1.2-1.3 across the board and it works great at shorter distances (i.e. in a caravan) so I don't really need to mess with it. But the perfectionist in me is always looking for the best way to make it as ideal as possible.
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Old 12-12-2011, 10:21 AM   #5
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Old 12-12-2011, 09:43 PM   #6
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Old 12-13-2011, 02:35 AM   #7
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Originally Posted by jeffk813 View Post
The length of your coax has NOTHING to do with how well your system is tuned. It's a myth. Notice that your SWR, while lower, was still high even after you added the extra coax, and didn't come down until AFTER you adjusted your antenna length. The additional coax masked your high SWR due to the way radio waves propagate in a transmission line.

The ONLY way to tune your system is to adjust your antenna length. SWR will indeed be lowered by changing the coax length in some cases, but low SWR does NOT necessarily mean an antenna system is optimally tuned.

Here's a link explaining more about this...

Exposing the 18' CB Coax Myth

That may be so, but with the shorter coax, and the SWR spiked off he scale, I didn't want to start trimming the antenna because I wasn't sure if that was the issue. By using the longer coax, it let me know where I was at.
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Old 12-14-2011, 09:58 AM   #8
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That brings up two questions:

1) If the optimum length of coax is a function of wavelength and cable VF (presumably a value known to the cable manufacturer), are there people out there selling optimum-length coax?

2) Other than SWR, is there any other way to determine when an antenna is "optimally tuned"?
1) To make money, same reason they sell CAI's, and Oxygen Free Speaker Cables for $$$$.

2) There are a number of ways, a RF current meter in line between the radio and the antenna, an antenna analyzer. The SWR meter is the cheapest and will usually get your antenna system to a decent working configuration. Not perfect but usable. For the type of usage expected of a CB it's fine.
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Old 12-14-2011, 10:16 AM   #9
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1) To make money, same reason they sell CAI's, and Oxygen Free Speaker Cables for $$$$.

2) There are a number of ways, a RF current meter in line between the radio and the antenna, an antenna analyzer. The SWR meter is the cheapest and will usually get your antenna system to a decent working configuration. Not perfect but usable. For the type of usage expected of a CB it's fine.
Okay, but for #1, I would think that having a superior cable (superior because it's the ideal length given the wavelength and VF) would allow you to charge more, even for a shorter cable, because of the better results. Besides, how much extra money are they really making on a $13 cable? Ehh, whatever. Mine's working fine, I'm not going to over-analyze it.
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Old 12-14-2011, 11:08 AM   #10
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Not to drag this on because if it's working that is what matters, just some further explination.
The cable is not superior because this is no ideal length. Actually have a cable length as a fractional wavelength of the working frequency can be detremental because it can mask any actual problems.

To go a little further as why SWR indication is not the best way to set up a system, a dummy load will have a SWR of 1:1. You have a match, and will not radiate anything. A resonate cable can act as a dummy load, and give you a perfect match, and not transfer any signal to the antenna. Again no usable radiation.
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Old 12-14-2011, 12:33 PM   #11
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In my experience with CB and ham radio antennas over the last 35 or so years, coax length does matter.
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Old 12-15-2011, 07:09 AM   #12
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Sure it matters from the standpoint of loss. The more cable you have absorbing the RF it carries, the less of that RF reaches and is radiated by the antenna. If the antenna isn't the correct length, or if there are other factors such as a poor counterpoise for the antenna to work against, it's going to reflect RF back into the feed line. RF in a feed line is making heat, plain and simple.

The optimal length of a transmission line is the shortest length required to connect the radio and the antenna. Period. The transmission line's sole function is to get the transmitted power TO the antenna, and bring the received signals back FROM the antenna. The antenna itself has the job of radiating signal. You can have a perfectly flat SWR but if your antenna sucks, nobody will hear you. Rather than wasting all this time with the coax, your time would be better spent adjusting the antenna properly.

High SWR is a symptom of a poorly adjusted antenna. Using a piece of coax to "fix" this is like putting a bucket under a leaky roof to "fix" the leak.

Oh, and I myself have 17 years of CB and ham radio experience of my own.
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Old 12-16-2011, 05:17 AM   #13
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While Jeff is right, to a point, it's important to remember that the feedline (coax) and antenna work together as a tuned system. There are certain lengths of coax that work better. Yes, the quick answer is for LOSS is the shorter the better. However, there's more in play than just loss. There's impedance. The lowest SWR is not ALWAYS the best IMPEDANCE match. For a 4 watt CB install the lowest SWR is really all you have to worry about. Sometimes you have to add coax to achieve that. Everything, and I mean EVERYTHING hinges on a really good ground. I've done a lot of ham radio HF mobile over the years and a proper ground is the most critical aspect of it all.
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Old 12-16-2011, 06:59 AM   #14
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Hi guys I have a question for y'all I haven't installed it yet but but my cb antenna came with aluminum mounting brackets will this give me a good ground?
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Old 12-16-2011, 04:11 PM   #15
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Okay need help from resident CB specialist....installed CB a few weeks ago....just got hold of SWR and all my readings are in the red and stay there.....i haven't used the cb other than to listen to the weather....i have a 4' tuneable tip firestick and its turned all the way in.....whats my next step...I'm not comfortable cutting into the antenna as I'm not quite sure what is meant by shortening it....
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Old 12-16-2011, 10:38 PM   #16
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Hi guys I have a question for y'all I haven't installed it yet but but my cb antenna came with aluminum mounting brackets will this give me a good ground?
Aluminum will ground just as good as any other unpainted or non powder coated metal. Star washers under the mounting screws will help make sure you get a good electrical connection.
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Old 12-16-2011, 10:40 PM   #17
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Okay need help from resident CB specialist....installed CB a few weeks ago....just got hold of SWR and all my readings are in the red and stay there.....i haven't used the cb other than to listen to the weather....i have a 4' tuneable tip firestick and its turned all the way in.....whats my next step...I'm not comfortable cutting into the antenna as I'm not quite sure what is meant by shortening it....
How and where is the antenna mounted? My first guess would be a grounding problem. Have you pinched or kinked the coax? Did you solder the PL plug on the end or is it factory molded on there? You could have shorted the braid and center conductor inside the plug.
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Old 12-17-2011, 08:55 AM   #18
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ant is mounted onto the ruged ridge spare tire mount....gonna double check coax for pinch....the antenna is the fire stik k-8r18 18 foot fire-flex coax cable with fire ring... i'm gonna double check that and make sure the ring isn't upside dow....and last but not least i'm gonna add a ground strap...
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Old 12-17-2011, 09:30 AM   #19
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Aluminum will ground just as good as any other unpainted or non powder coated metal. Star washers under the mounting screws will help make sure you get a good electrical connection.

Awesome thanks
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Old 12-20-2011, 08:17 AM   #20
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Instead of shortening the antenna (which you can't do, since it's all the way in) try lengthening it. Short amounts, 1/8" at a time and check the SWR each time. See if that improves things.
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Old 12-20-2011, 08:25 AM   #21
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What do you do for one of those fiberglass ones that you can't adjust?
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Old 12-20-2011, 09:07 AM   #22
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The fixed-length fiberglass antennas are a but more difficult to adjust, but I know some guys who have been able to tweak a little bit by using washers between the antenna and mount to lengthen it. You obviously can't have too many there, since you're losing threads with every washer, but it may not take much. You also can't do anything to shorten it. This is one reason I always recommend an adjustable antenna. If you can't adjust the length you're limited to moving it to a different area of the Jeep that may provide a better ground plane.
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Old 12-20-2011, 09:13 AM   #23
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The fixed-length fiberglass antennas are a but more difficult to adjust, but I know some guys who have been able to tweak a little bit by using washers between the antenna and mount to lengthen it. You obviously can't have too many there, since you're losing threads with every washer, but it may not take much. You also can't do anything to shorten it. This is one reason I always recommend an adjustable antenna. If you can't adjust the length you're limited to moving it to a different area of the Jeep that may provide a better ground plane.
Cool thanks for the info!

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