High SWR with my CB Install
10-07-2005, 08:12 AM
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High SWR with my CB Install
Hi All,
This is my first post in the yotatech forums, however I have found a tremendous amount of information on yotatech. Let me say thanks for the past info and hopefully thanks for the future, if you can give me some insight.
I installed a Cobra Cobra 29 WX NW ST in my '95 4Runner. I have a 4' Firestik antenna with a heavy duty Firestik spring on top of a quick disconnect. My mount is exactly the same as 4RunnerKid's. It is right above the rear taillight on the driver side and is mounted on the inside of where the tailgate closes. My coax runsalong the inside of the side panels and under the bottom door panels all the way up to the dash. We got pretty creative with our mounting since the cb is so large, I didn't quite realize that when I bought it. I'm a gadgets kind of guy and the more knobs and buttons the better in my opinion. So we removed the two center air vents and ended mounting the cb in the space where the air vents used to be after removing the center divider. We sealed the air duct that lead to those vents and now I have even better air flow out of the two side vents than I did with all 4. The size of the opening and the size of the cb are a very good match. I'll have to post some pics when I get them off of my buddy's camera.
We tested continuity everywhere and everything checked out, however when I go to calibrate the swr, it has a built in swr meter, and switch to swr on the unit, I get the needle jumping all the way to the right on every channel. All of the reading I have done suggests that there is a short somewhere that is causing this, however I have checked everything. A poor gound plane at the antenna was also suggested and I even attached a seperate ground wire directly from the chassis to the antenna mount and still nothing changed. I have adjusted the screw on the end of the firestik as well and it didn't change.
By turning the cal knob on the unit when in the swr position, the needle does move to any point I want, however I didn't think that this was the proper way since it messes with the calibration setting.
My buddy who helped me install mine also installed one in his truck and is having the same problem. We both live in Los Angeles and there aren't a whole lot of places that know anything about tuning a cb around here.
If you can offer any assistance, I would greatly appreciate it.
This is my first post in the yotatech forums, however I have found a tremendous amount of information on yotatech. Let me say thanks for the past info and hopefully thanks for the future, if you can give me some insight.
I installed a Cobra Cobra 29 WX NW ST in my '95 4Runner. I have a 4' Firestik antenna with a heavy duty Firestik spring on top of a quick disconnect. My mount is exactly the same as 4RunnerKid's. It is right above the rear taillight on the driver side and is mounted on the inside of where the tailgate closes. My coax runsalong the inside of the side panels and under the bottom door panels all the way up to the dash. We got pretty creative with our mounting since the cb is so large, I didn't quite realize that when I bought it. I'm a gadgets kind of guy and the more knobs and buttons the better in my opinion. So we removed the two center air vents and ended mounting the cb in the space where the air vents used to be after removing the center divider. We sealed the air duct that lead to those vents and now I have even better air flow out of the two side vents than I did with all 4. The size of the opening and the size of the cb are a very good match. I'll have to post some pics when I get them off of my buddy's camera.
We tested continuity everywhere and everything checked out, however when I go to calibrate the swr, it has a built in swr meter, and switch to swr on the unit, I get the needle jumping all the way to the right on every channel. All of the reading I have done suggests that there is a short somewhere that is causing this, however I have checked everything. A poor gound plane at the antenna was also suggested and I even attached a seperate ground wire directly from the chassis to the antenna mount and still nothing changed. I have adjusted the screw on the end of the firestik as well and it didn't change.
By turning the cal knob on the unit when in the swr position, the needle does move to any point I want, however I didn't think that this was the proper way since it messes with the calibration setting.
My buddy who helped me install mine also installed one in his truck and is having the same problem. We both live in Los Angeles and there aren't a whole lot of places that know anything about tuning a cb around here.
If you can offer any assistance, I would greatly appreciate it.
10-07-2005, 09:08 AM
#2
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This exact thing happened to me when I installed my midland and 3' firestick unfortunately I never figured out exactly why. What I think finally fixed it was loosening the bolt that held my spring and antenna to the mount. My best geuss is that it was too tight and contact was made somewhere that is wasn't supposed to be. The reason I loosened it is that I did exactly what you did, I checked for continuity everywhere, there were no issues with opens or shorts, it was properly grounded, I even added an auxiliary ground like you did. I finally got fed up and tried another antenna and coax and that didn't work, then I tried removing the spring. When I did this I left it barely even hand tight because I was going to need to put it back and it magically started working, I put the spring back in and tightened it just enough that it would stay on. So as stated above, I assume I tightened it down to much and contact was made somewhere where it wasn't supposed to be. Give that a try. If nothing else try talking to Firestik and check out their website, they have a good tech section. http://www.firestik.com/Tech_Docs.htm
10-07-2005, 11:27 AM
#4
Registered User
Try an external SWR meter.
If your still having problems its most likely a bad ground plane problem. (ground plane is NOT a ground on the antena but the surface the antenna needs to radiate off of)
If your still having problems its most likely a bad ground plane problem. (ground plane is NOT a ground on the antena but the surface the antenna needs to radiate off of)
10-07-2005, 12:08 PM
#5
Firestik has some good SWR docs on-line:
- http://www.firestik.com/Tech_Docs.htm
Are you testing the SWR properly? Usually a bit tricky to do it right with a built-in meter. On my old Uniden Grant, you turn the SWR/RF knob to the CAL position, key up on any channel and adjust the needle with the Calibrate knob to point to the spot indicated by the manual, usually full scale. Then you switch the knob to SWR, key up on Ch.1 and 40 and then read the SWR (w/o changing the Cal knob) on both channels and adjust the antenna to compensate, longer if Ch.1 is higher and shorter is Ch.40 is higher.
But if you are testing properly, it is likely a grounding issue. Did you see any tiny little change after adding the ground wire? I had a similar problem on my rear tire carrier mounted antenna. I found a tiny improvement (like from 3.0 to 2.7) when I added a heavy ground wire. I had DC continuity from the carrier to the frame and body, but I suspect the RF continuity was not there. So I ended up moving the antenna to the rear part of the body and it's worked fine since:
http://www.4crawler.com/4x4/CheapTri....shtml#Antenna
One other thing to try is swapping parts, coax and antenna if possible. I once had a coax go bad after a number of years use, looked fine externally and ohmed out fine, but the SWR was sky-high. I swapped the antenna off my other rig, same reading, got a new cable, hooked it up and SWR back to 1.2 or so.
- http://www.firestik.com/Tech_Docs.htm
Are you testing the SWR properly? Usually a bit tricky to do it right with a built-in meter. On my old Uniden Grant, you turn the SWR/RF knob to the CAL position, key up on any channel and adjust the needle with the Calibrate knob to point to the spot indicated by the manual, usually full scale. Then you switch the knob to SWR, key up on Ch.1 and 40 and then read the SWR (w/o changing the Cal knob) on both channels and adjust the antenna to compensate, longer if Ch.1 is higher and shorter is Ch.40 is higher.
But if you are testing properly, it is likely a grounding issue. Did you see any tiny little change after adding the ground wire? I had a similar problem on my rear tire carrier mounted antenna. I found a tiny improvement (like from 3.0 to 2.7) when I added a heavy ground wire. I had DC continuity from the carrier to the frame and body, but I suspect the RF continuity was not there. So I ended up moving the antenna to the rear part of the body and it's worked fine since:
http://www.4crawler.com/4x4/CheapTri....shtml#Antenna
One other thing to try is swapping parts, coax and antenna if possible. I once had a coax go bad after a number of years use, looked fine externally and ohmed out fine, but the SWR was sky-high. I swapped the antenna off my other rig, same reading, got a new cable, hooked it up and SWR back to 1.2 or so.
10-07-2005, 09:19 PM
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If you get desperate, send me a pm. Somewhere I have the business name and address for the place I went to have mine SWR'd. Was an old guy who had been around CB's when they were big in the 70's.
As I recall the place is near North Hollywood, if that's close to you.
As I recall the place is near North Hollywood, if that's close to you.
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10-09-2005, 02:10 PM
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Problem Solved
Hey All,
Well, we got everything working properly. We had used a twist on pl-259 connector to connect the coax at the head unit. This was done as a result of not having an adapter for RG-58 coax to fit inside a standard pl-259. The connector was the problem. so I would advise not using the screw on solderless type. In order to get a good connection, we needed to solder on a pl-259 with the appropriate adapter. Anyways, after getting the dash back together, we calibrated and switched over to swr. With a little tuning, I am now reading 1.2 on channel 1 and 1.3 on channel 40. I'm very happy. Thanks for all of your help.
Well, we got everything working properly. We had used a twist on pl-259 connector to connect the coax at the head unit. This was done as a result of not having an adapter for RG-58 coax to fit inside a standard pl-259. The connector was the problem. so I would advise not using the screw on solderless type. In order to get a good connection, we needed to solder on a pl-259 with the appropriate adapter. Anyways, after getting the dash back together, we calibrated and switched over to swr. With a little tuning, I am now reading 1.2 on channel 1 and 1.3 on channel 40. I'm very happy. Thanks for all of your help.
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