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Old 04-14-2014, 03:45 PM   #1
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Another high SWR problem... Sorry

Sorry to bring up the high SWR problem again. I have searched the forum and all the solutions listed from past problems I have eliminated. What am I missing?

I am seeing SWR reading of well over 3, but it is not pegging the meter.

Here is what I am working with

Cobra 75 WXST installed behind the glove box
4 foot FireStik II antenna mounted on LoD tire carrier antenna mount
18 feet of FireStik Fire-Flex coax cable with Fire-Ring antenna connection
Spring for the above mount
AUSWR SWR meter

I knew that the ground would be an issue so I ran a braided cable from the antenna ground to the chassis. I used a Ĺ ring lug at the ground connection of the Fire-Ring connector at the antenna mount.
There is continuity from the radio end of the coax to the chassis. Well less than 1 ohm.
There is continuity from the center pin of the coax at the radio to the antenna stud. Once again well less than 1 ohm.
There is NO continuity between the center pin and the shell of the connector at the radio. Greater than a meg ohm

I tried this with the spring and without. No substantial change. I have adjusted the screw top on the antenna and I am not anywhere close. I even stuck a longer screw in the top of the antenna to see if that got me any closer.

Things I have not yet tried.
A different antenna. I will have to borrow a friendís antenna to do this.
A different cable
A different radio
A different SWR meter

When checked with a multi-meter using low voltage DC everything checks out. I know enough about RF to know that things happen when you put high frequency AC into a system. I am just not smart enough to sort out what that means I should do.

I am feeling like a real doofus right now, so any ideas would be appreciated. If you need pictures I can do that, but I did not take any during the install.

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Old 04-14-2014, 06:26 PM   #2
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Check the install again. Make sure you have a nylon washer between the mount and your spring. Make sure you have the swr meter connected properly, it happens. After that, I would take the spring off and disconnect the antenna ground, check the readings and go from there.

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Old 04-14-2014, 09:34 PM   #3
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I have done all that but removing the ground. I will see what that does.
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Old 04-15-2014, 12:15 AM   #4
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New Jeep

Assigning probabilities to your symptoms, the grounding is the most likely cause. You say you grounded via braided cable to the chassis. If you mean, to the frame, only, that would be an error. Sheet metal ground is most important, followed by adding the frame if needed. The best ground possible would be to pierce the powder coat and paint right at the antenna mount and avoid the loss caused by a length of strap. Internal or external stainless star washers are excellent for this.

As an engineer, you may have a fleeting knowledge that two wire resistance measuring instruments are not suitable for low resistance measurements below 5 ohms, so your readings are inconclusive at best.

Since you elected to use a Fire Ring cable, you are unable to properly measure all aspects of your system that could give valuable info, but although the antenna could be the trouble, I would expect it to peg the meter.

If you continue to have issues, I live close enough to you, if you want to invest an afternoon, to take a look. May be do a write-up on it.

Phil
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Old 04-15-2014, 04:39 PM   #5
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First to answer bbtj, I pulled the ground. The ohm meter indicated no continuity, so it was truly disconnected from ground. I got a slightly lower SWR, but still well above 3.

Phil, yes I am connected to the frame. If I were to connect to the tire carrier it would still be through the frame since that is what the whole thing bolts to (and all the parts are painted or powder coated). There are no connections to the tub (sheet metal). I can try to find a place that I can ground to the tub if you think that will help. I could just run something to the sub woofer enclosure through the back window for a test. It is not too hard to run coax on this thing since it just runs down the passenger side of the interior. The only challenge is getting into the interior. I ran up through the bottom of the passenger tail light area. Should I switch to a different cable? I have a K4 stud and could therefore switch to something with a couple of ring lugs at the antenna mount. I also have a hood lip mount that I was planning to use for a VHF/UHF antenna in the future. I did not anticipate that this was going to be such an ordeal. I am not overly concerned about having the ultimate range. I just don’t want to kill the transmitter. This is mostly to comply with communications on the trail dictated by some of the local clubs. For range I will go to a ham rig.

I live in San Ramon and love kayaking on Elkhorn Slough and hiking down at Point Lobos. The last time I was down there with the family we stopped in Castroviile (to get out of the traffic jam) at that BBQ place that is on the main drag. They had very good BBQ. My teenage boys loved the size of the servings.

Thanks for your interest.
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Old 04-15-2014, 07:12 PM   #6
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First to answer bbtj, I pulled the ground. The ohm meter indicated no continuity, so it was truly disconnected from ground. I got a slightly lower SWR, but still well above 3.

Phil, yes I am connected to the frame. If I were to connect to the tire carrier it would still be through the frame since that is what the whole thing bolts to (and all the parts are painted or powder coated). There are no connections to the tub (sheet metal). I can try to find a place that I can ground to the tub if you think that will help. I could just run something to the sub woofer enclosure through the back window for a test.
Thanks for your interest.

The surface area of the body sheet metal is what the antenna uses as a ground plane. (this is a gross simplification) Grounding only to the frame will force RF currents through the factory supplied grounding straps that are some distance away from the antenna, inducing extreme ground loss, trying to energize the sheet metal, while increasing VSWR. An antenna, under these conditions will possibly not trim down in frequency to center in the CB band. An ungrounded CB antenna resonates 1 to 1.6 Mhz higher than a grounded one. For an example, the four foot Fire Stick only has a tuning range of 1.1 Mhz and thus will run out of adjustment long before there is any indication of approaching resonance on the VSWR meter. This gives the appearance that nothing is happening as you tune and is very confusing.

I am not convinced that the jumper to the sub woofer will be sufficient. Length is the main issue, as well as surface area of the braid / wire used. In my opinion ground jumpers over 4 inches long, no matter the width, should be avoided.


Later edit: It is apparent by your ground removal and measurement, that grounding is your main / only issue. Save other things (cable, connector, etc. for last resort.

Phil
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Old 04-16-2014, 12:19 AM   #7
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There is nothing within 4 inches. The nearest body work is going to be feet away. I am using braided eletrical bonding wire we use at work for grounding systems in RF enviroments. It is about 1/4 inch wide. You have to wonder about the people that sell these mounts and if they own an SWR meter. I could try the hood mount I have. That has good grounds right next to the mount. I just hate to waste that on a CB. It sounds like I have some more experiments to do.
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Old 04-16-2014, 09:29 AM   #8
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I checked on some of the reviews about the Firering coax and found some that had the same problem as you. Here is the link, in case you haven't looked at these already, Amazon.com: Customer Reviews: FireStik K-8R18 18 foot Fire-Flex coax cable with Fire-Ring. Hope this helps. I read a couple where the people called Firestix, and they apparently walked them through the install.
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Old 04-16-2014, 11:57 AM   #9
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There is nothing within 4 inches. The nearest body work is going to be feet away. I am using braided eletrical bonding wire we use at work for grounding systems in RF enviroments. It is about 1/4 inch wide. You have to wonder about the people that sell these mounts and if they own an SWR meter. I could try the hood mount I have. That has good grounds right next to the mount. I just hate to waste that on a CB. It sounds like I have some more experiments to do.
bbtj; Good research!

New Jeep; After trying the extended ground strap, a revisit to the details bbtj uncovered would be in order I suppose, I would then do an experimental install of the hood mount. No need to special route the coax, just let it hang out the window and see if any joy ensues. I know you will eventually get it.

Your comment on meters and mount makers applies double to Fire Stick. They are completely ignorant on transmission line theory and it is revealed openly on their website.

Good luck
Phil
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Old 04-16-2014, 05:06 PM   #10
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I did research ahead of time on how the mount goes together because like the comments on Amazon there are no instructions. My cable did not need to be soldered since it uses a miniature UHF connector that adapts to the PL259 mating connector. The cable I bought came with the K4R stud and all of the washers. I did end up adding one more washer to make the installation easier. Here is the order from bottom to top.

Fire Ring connector which has the 3/8-24 thread permanently attached (it is not a separate bolt) and the ground surface outside of the 3/8 bolt
1/2 inch ring lug with the ground wire attached
Nylon washer with a slight 1/2 inch shoulder down (this is what I added because it kept the ground ring lug from shorting to the 3/8 thread that carries the signal, I have good contact because the ring lug is firmly sandwiched)
The mount on the Jeep with a 1/2 inch hole
Another nylon shoulder washer with the shoulder down.
3/8 flat washer
3/8 split ring lock washer
K4R stud
Spring
Antenna.

That gives me the contact to ground, the signal contact through the stud to the antenna, and isolation between signal and ground.

I will play with the ground and see what that does. I might try another antenna if I can swipe one from a buddy’s rig. After that I will try moving to the hood mount and see what that does. I have another cable and another stud on order that use the PL259 connectors. I also have a stud that uses ring lugs. With all that I am only lacking another radio. I solve problems for a living, but I am not an electrical guy so I revert to swap and test with these problems. I know basic electrical, but when it comes to RF, that is an alternative reality in my mind. I guess the first step in the 12 step RF recovery process is admitting that you don’t know what you are doing.
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Old 04-17-2014, 08:52 AM   #11
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Try running the ground to the tub, which means you are going to have to take off some of the paint. Just about all of the instructions I've read say to run it through the tailgate, by the coax, and pull up some of the carpet, grind off the paint and then attach the ground to the tub. Also, if you haven't already, take out the extra nylon washer that you say you added. Make sure you are over 30 feet away from any obstructions, I've seen people trying to tune their antenna while inside their garage.

Other than that, I'm out of ideas. I would refer you to rightchannelradios.com, and check out their resources section. They have detailed instructions on installations and trouble shooting.
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Old 04-21-2014, 10:16 PM   #12
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I have found the problem. This evening I replaced the cable with a standard RG85AU cable with PL259 connectors on both ends. The SWR came into 2.0 with no great effort. It seems that the Fire Ring cable is the problem. The cable was just run through the interior, so I still need to do a permanent installation. That will be this weekend. I did have to switch to another stud that had an SO259 connector on it, but those things are so simple there is no way that could have been the problem.
I used the ground on the frame of the Jeep. I tried moving the ground to the tub and got no improvement. I went in through the tail light assembly and drilled a hole in the sheet metal in there. No difference. I have not tried moving the ground with the new cable. I might try that this weekend.
I also moved the antenna to the fender mount and saw no difference with the new cable. It was still at 2.0, so I will mount the antenna on the back.
I cut a knuckle working on it this evening, so maybe that is the real reason it is working now. We have a saying at work that if you don’t bleed on the equipment it won’t work.
Thanks for the suggestions.
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Old 04-21-2014, 10:19 PM   #13
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Good to hear.
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Old 04-22-2014, 06:24 AM   #14
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Quote:
Originally Posted by New Jeep View Post
I have found the problem. This evening I replaced the cable with a standard RG85AU cable with PL259 connectors on both ends. The SWR came into 2.0 with no great effort. It seems that the Fire Ring cable is the problem. The cable was just run through the interior, so I still need to do a permanent installation. That will be this weekend. I did have to switch to another stud that had an SO259 connector on it, but those things are so simple there is no way that could have been the problem.
I used the ground on the frame of the Jeep. I tried moving the ground to the tub and got no improvement. I went in through the tail light assembly and drilled a hole in the sheet metal in there. No difference. I have not tried moving the ground with the new cable. I might try that this weekend.
I also moved the antenna to the fender mount and saw no difference with the new cable. It was still at 2.0, so I will mount the antenna on the back.
I cut a knuckle working on it this evening, so maybe that is the real reason it is working now. We have a saying at work that if you donít bleed on the equipment it wonít work.
Thanks for the suggestions.
Glad you found progress. My thread seems to be around the same issue.
CB install issue, short exists
The firering coax cables... I'm convinced aren't so great, but who knows. I was only able to get SWR down to 1.8, but I'll keep at it.
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Old 04-22-2014, 03:19 PM   #15
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I agree that the Fire Ring cables don't seem to be too good based on my experiance of two. Even with the new cable I am only able to get to 2.0. That is at least 2 watts of power going out as oposed to esentially zero with the other cable. I will see if I can get it better once I make the installation permanent this weekend. I have a meeting every night for the rest of the week, so I will not get to it until the weekend. At least the weather is suppose to be nice then.
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Old 04-22-2014, 03:34 PM   #16
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I agree that the Fire Ring cables don't seem to be too good based on my experiance of two. Even with the new cable I am only able to get to 2.0. That is at least 2 watts of power going out as oposed to esentially zero with the other cable. I will see if I can get it better once I make the installation permanent this weekend. I have a meeting every night for the rest of the week, so I will not get to it until the weekend. At least the weather is suppose to be nice then.
Not bad. I'd go with it. At a 2:1 SWR, you're still getting 3.6 watts out and should have respectable receive performance.

Also, should not risk the small power transistors.

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