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Old 01-14-2018, 12:49 PM
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Tuning a KW4 CB Radio Antenna in a JKU

Hello! I want to share my experience with this install, in hopes that I can save someone else a few hours of frustration. Firstly, here is the list of parts that I used for the install:

Cobra 75 JK Kit, packaged by Just Jeeps
Firestik Spring Mount
SWR Meter

This post is mostly in regards to the KW-4 antenna, but I will briefly mention the other aspects of my install.

Cobra 75 Radio: This radio comes with a handled mic that houses all the buttons and displays of the radio. The mic connects to a smaller control box under the dash which receives power, the antenna coax, and has the option to send out audio to an external speaker through an 1/8" headphone jack. I zip tied the control box in the dash just underneath the glove box. Ran the hot and ground wires through the firewall to engine compartment. Hot directly on the battery, and the ground tied into a ground point on the body.

18' Coax Cable: This cable has a PL295 connector on each end, which makes connecting simple, but routing was a challenge. Most guides will tell you to run the cable straight, avoiding coils and tight corners. 18' of cable seems to be the perfect length to be able to do so in a JK Unlimited. I ran mine from the glove box, up the passenger A pillar, along the sports bar (just under the velcro fabric cover), down the sports bar in the trunk, behind the subwoofer panel, where it then met up with the other wires going into the tail gate. I followed the path of the other tail gate wires, and was able to pop out to the outside through a hole I had cut in a rubber plug.

Stud Mount: Make sure the mount makes contact with the antenna bracket to ensure a ground connection. Use the plastic isolation ring to keep the stud (the hot) from making contact with the bracket (the ground).

Firestik Heavy Duty Spring: Not much to say here, the spring works great to give your antenna a bit of flex. Remember, this also adds "length" electrically to your antenna and will effect how you tune it. Worth noting that the spring carries the hot only, and there shouldn't be any continuity from the spring to the ground.

TeraFlex CB Antenna Mount: As with most mounts, the will have a layer of powder coat that will prevent the stud from grounding to the mount. Where your stud connects (and ground wire if applicable) you will need to clean off the paint down to bare metal to make that connection.

Firestik Original KW-4' Antenna: Now onto the Antenna... For the life of me, I could not seem to solve what I thought was a ground problem. After my install was complete, I was getting SWR readings of 5+ on all channels. After checking many knowledge bases on the internet about CB Radios, I always came back to the same answer. High SWR = Grounding Issue. I took my system apart countless times, and used a multimeter to check continuity through all my parts, check for shorts, and confirm my ground was rock solid. Every time, it checked out, but still I would get bad SWR readings. After giving up, I emailed Firestik. This is where it gets interesting. Firestik told me that the original KW4 Antennas (not the KW II's with the tunable tip) were originally designed for truck tractor's, and had compensated for the amount of fibreglass in a tractor by adding 8 extra winds to the antenna. For reference, the popular Firestik FS4 Antenna with the tuneable tip has 8 less winds than the KW4. Therefore, what seemed to be a very bad ground issue, was just a tuning issue all along. I started by removing 2 winds from the antenna, then 1, then 1/2 winds incrementally. Once 8 winds were removed it became clear to see that this was a tuning issue and not a ground issue. After removing a total of 11 winds from the KW4 antenna, it was finally tuned to a comfortable SWR reading of 1.0 on Ch1 and 2.0 on Ch2. This is still considered electrically long, but readings under 2.0 are acceptable for operation according to Firestik.

TL;DR: The original Firestik KW series antennas have 8 extra winds at their tip that need to be removed before being tuneable on a JK.

Before my tuning process, I ran a dedicated ground wire to try and solve the problem. The wire is a 12AWG stranded cable, running from the antenna mount, through the tailgate cable patch, and is tapped into the body under the trunk panels. I can say that this did improve my antenna's ground connection by a lot, but I can't speak to how it effected my SWR because I had left it connected during the entire tuning process.

I would highly recommend using a multimeter to check continuity before install, and check for shorts and a proper ground after your install. Do this before connecting the radio and keying up the mic button.

I've added some pics here. One of my test results after trimming, with the spring installed. Another of the tip of the KW4 Antenna.

Useful Resources:
The Firestik website has great articles on tuning and troubleshooting: CATALOG Main Page (Frame Setup)
The Right Channel Radios website is also a great database: https://www.rightchannelradios.com/




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Old 01-15-2018, 07:50 AM   #2
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First thing I would have recommended is to test without the spring installed.

That would confirm where the problem was/is.

Not sure about your SWR readings? 1:1.0 is perfect and getting that should mean everything is good. But! Having that on channel 1 then going to 2:1 on channel 2 means something is wrong. Most installations have the SWR tuned on channel 19 or 20. That way you can go to 1 or 40 and likely still have an acceptable SWR reading.

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Old 01-15-2018, 03:33 PM   #3
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k_dipietro, did you really mean Channel 2, or was it Channel 40 for your higher SWR value?
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Old 01-15-2018, 07:21 PM
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Originally Posted by Airstreamer67 View Post
k_dipietro, did you really mean Channel 2, or was it Channel 40 for your higher SWR value?
Definitely meant ch40, not ch 2. I will update that, thanks!
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Old 01-15-2018, 07:28 PM
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Quote:
Originally Posted by realshelby View Post
First thing I would have recommended is to test without the spring installed.

That would confirm where the problem was/is.

Not sure about your SWR readings? 1:1.0 is perfect and getting that should mean everything is good. But! Having that on channel 1 then going to 2:1 on channel 2 means something is wrong. Most installations have the SWR tuned on channel 19 or 20. That way you can go to 1 or 40 and likely still have an acceptable SWR reading.
Initially, I did do all my testing and troubleshooting with the spring not installed. My readings were still very high, and appeared to be a ground issue, not a tuning issue. Once you pass 3-4 on my SWR meter it becomes a bit harder to read. It wasn't very clear what the slight difference was that the spring made.

Ch2 was definitely a typo, my bad! I was getting a reading of 2.0 on Ch40. According to this article by Firestik 2.0 is an acceptable reading for operation.
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Old 01-17-2018, 01:50 PM   #6
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Firestick threw you a curve with that stuff about the antenna being tuned to offset all the non-metal big-truck cabs. They should have at least put a tune-able tip on that antenna if they expect them to be used on metal ground planes too. On the other hand, a tuneable tip might not have enough range to work on that antenna due to its design to accommodate fiberglass cabs.

Your SWR split of 1.1 on Channel 1 and 2.0 on Channel 40 indicates the antenna is still too "long." I'd trim off a bit more wire, which probably would get the values a bit closer. While the 2.0 on Channel 40 is likely not damaging to anything, it does reduce the antenna's efficacy by about 10% on that end of the channel scale, so improving the SWR a bit more would be desirable but not necessary.

If you do decide to try to improve the SWR values, be careful to cut short sections at a time while testing to prevent going too far with it. That antenna should be able to get the values closer, perhaps to 1.3 SWR or so on Channels 1 and 40, which should result in a better SWR than either end of the poles on the all-important-for-highway-travel channel, the Trucker's Channel 19 (or 17 in some places on the West Coast).
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Old 01-18-2018, 05:47 PM
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Originally Posted by Airstreamer67 View Post
Firestick threw you a curve with that stuff about the antenna being tuned to offset all the non-metal big-truck cabs. They should have at least put a tune-able tip on that antenna if they expect them to be used on metal ground planes too. On the other hand, a tuneable tip might not have enough range to work on that antenna due to its design to accommodate fiberglass cabs.

Your SWR split of 1.1 on Channel 1 and 2.0 on Channel 40 indicates the antenna is still too "long." I'd trim off a bit more wire, which probably would get the values a bit closer. While the 2.0 on Channel 40 is likely not damaging to anything, it does reduce the antenna's efficacy by about 10% on that end of the channel scale, so improving the SWR a bit more would be desirable but not necessary.

If you do decide to try to improve the SWR values, be careful to cut short sections at a time while testing to prevent going too far with it. That antenna should be able to get the values closer, perhaps to 1.3 SWR or so on Channels 1 and 40, which should result in a better SWR than either end of the poles on the all-important-for-highway-travel channel, the Trucker's Channel 19 (or 17 in some places on the West Coast).
Hey! What I found strange is that no where on the internet did I see anyone mention the 8 extra winds for fibre glass glass cabs. Not on any of the vendors sites, not Firestik's, and not in the forums. That was part of my reasoning to start this thread. Seems something that would be valuable to know when selling the product. Like I mentioned though I came across the antenna as a part of the CB Kit that I had bought, so was SOL when I realized it was a KW4 antenna and not the FS4, though I didn't know the difference at the time. Firestik did mention after that I need to take off 8 winds before I get to the long end of the FS4 tunable antenna, so it seems you're right in thinking that it's too long even for a tunable tip.

Yes the antenna is still long. I wanted to first get it down into the useable range. It was a big small victory for me so I felt like sharing, hah.
I'll likely wait for the warmer weather before I start cutting again.

Thanks!

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