High SWR -- tried everything!

[jsmoriss]

I used to have a decent SWR, but then it turned bad, and I suspected my coax. My antenna was mounted on my tailgate, and my coax would bend every time the gate would open/close. I just change my rear bumper, and changed the coax (routing it from the outside, so no more bends). I dissected the coax and found the core was broken. I cleaned up some rust here & there and redid everything. I used a multimeter to check the ground, etc. -- everything looks perfect. I just can't seem to get the SWR lower than 2 (using internal or external SWR meter). I tried different antennas (4' firefly, 5' wilson), coax (18+9, 18, 30), and even connected the CB directly to another battery. I feel like I've tried every possible combination, and still can't get a decent SWR. The only thing I can think of that might be the culprit is the CB itself. Is it possible that by using it with a bad coax, I could have damaged it, and the only hint of this damage affects the SWR?

Thanks,
js.

 

[jsmoriss]

Oh, I forgot to mention that my CB is a Cobra 29WXNWST.

Thanks,
js.

 

[goodtimes]

From your avatar, it looks like you are driving a JK? How far from your top is the antenna? How far above it?

I had the same problem with my TJ....even with a top loaded fiberglass antenna (4', and a 5', IIRC) I couldn't get my SWR down. Then I tested it one day with the top down....all was well. Put the top up...not so good anymore. After talking with the local radio shop, we believe that the antenna just wasn't high enough (above the roof line). I ended up putting a 1/4 wave stainless antenna on it, and haven't looked back.

 

[jsmoriss]

From your avatar, it looks like you are driving a JK? How far from your top is the antenna? How far above it?

I'll take a picture later, but the antenna is much higher than it used to be -- a good 2/3rd or more above the roof line (and roof rack). My SWR used to be 1-1.5 lower down. This is a new bumper and tire carrier though. The ground checks out everywhere, BUT the tire carrier is at an angle (Expedition One bumper & carrier for the JK). I wonder if:

1- The antenna is too far from the ground plane.
2- The ground plane immediately bellow the antenna is at an angle.
3- I blew the CB when the old coax shorted.

Any thoughts on #3? I have until Wednesday to buy another if the CB could be the cause. I'm going to do a little more testing today, including moving the mount to the tailgate (where it used to be) instead of the tire carrier.

js.

 

[rusty_tlc]

As a suggestion I would pick up a cheap Radio Shack / Uniden CB and use it to test the antenna install. I think you can finds a basic unit for under $50.
If it tunes okay you know you have a problem with your Cobra. If not you can look into the antenna install. Either way you have an inexpensive backup radio.

 

[jsmoriss]

A little update...

When I have the radio on, and I press transmit, I'm getting very loud static in the speakers.

Any ideas on what could be causing this? I went through the whole system and didn't find a short, so I've no idea...

Thanks,
js.

 

[jsmoriss]

I changed the antenna mount since the old one had been mounted outside for a while, so you never know. It cleared up the HU speaker problem, but I still have a 3-4 SWR. This is getting really frustrating... I have a new CB on it's way for Wed-Thu, but we're leaving Thursday morning, so I may not get it in time... Meanwhile, I'm going to try and connect the CB to an independent battery (again) AND run a new 18' coax between the CB and antenna (again). Although my ground checks out, maybe there's a 'ground quality' issue I'm missing... Or maybe it's just the CB that's defective.

js.

 

[jsmoriss]

BTW, here's a shot from Saturday when we installed the new rear bumper...

There's a ground strap between the tire carrier and tailgate, and there's another strap between the tailgate and body. Even without the straps, there's a continuous ground, but I still prefer to make sure. I added a coil spring to the antenna later, so it's a few inches taller now.

js.

 

[gary in ohio]

A little update...

When I have the radio on, and I press transmit, I'm getting very loud static in the speakers.

Any ideas on what could be causing this? I went through the whole system and didn't find a short, so I've no idea...

Thanks,
js.

High swr will feed back into the speaker. My bet is water in the coax. If you had a break in the coax and it got wet there will be water in it. Replace the coax. I would also look at the antenna. If its whacking branches its possible you cracked the antenna wire. You may never see it outside but it may still be cracked.

 

[jsmoriss]

High swr will feed back into the speaker. My bet is water in the coax. If you had a break in the coax and it got wet there will be water in it. Replace the coax. I would also look at the antenna. If its whacking branches its possible you cracked the antenna wire. You may never see it outside but it may still be cracked.

Thanks Gary. I replaced the original coax already, and yesterday I replaced the antenna mount. I'm using an older 4' and a new 5' antenna. Nothing seems to work. So today, just to make sure (again), I used a dedicated battery for the CB and a different 18' coax. I'm still getting 3-4 SWR, so now I'm pretty sure it's the CB. I have a new peak & tuned CB on the way, so hopefully that'll fix the problem.

js.

 

[gearbox]

Maybe a No Ground Plane setup?

 

[gary in ohio]

I used a dedicated battery for the CB and a different 18' coax. I'm still getting 3-4 SWR, so now I'm pretty sure it's the CB. I have a new peak & tuned CB on the way, so hopefully that'll fix the problem.

Being that SWR is a ratio of transmitted power to reflected power I DOUBT its the radio, If the radio is transmitting the SWR is determined by the load, not the source. Is it possible the SWR meter is defective?

 

[jsmoriss]

Being that SWR is a ratio of transmitted power to reflected power I DOUBT its the radio, If the radio is transmitting the SWR is determined by the load, not the source. Is it possible the SWR meter is defective?

The CB has an SWR meter, but I also used an external meter to double-check the CB's reading, and they match. At 3-4 it should be something obvious, but I'm pretty sure everything is ok. I've tried an 18', 18+9', and a 30' coax. If the CB doesn't fix it, then maybe I'll try an 18+18' coax. And as gearbox suggested, there's always a no-ground-plane antenna.... Unfortunately, that's about the only thing I don't have in my pile of parts.

js.

 

[soonenough]

I realize this is slightly off-topic, but you mentioned that you're trying different combinations of coax length. You might want to consider eliminating any extra length of coax, as the whole 1/4-wave or 1/2-wave coax length thing isn't all it's cracked up to be. I seriously doubt that's what's causing the high SWRs you're getting, but it could be hurting you slightly. More reading on this subject here.

And when the author of that article is referring to "XXXXX CB manufacturer", he's talking about FireStik and their online Tech Section, which can be found here. It's actually a really helpful section, as long as you keep in mind that selling parts is their top priority. I'd suggest looking it through for other ideas of what might be causing your high SWRs. IIRC, they have an article specifically on mounting antennas to tire carriers.

 

[jsmoriss]

Woohoo! Ok, here's the good news and the bad news.

- The bad news is the new CB gives the same result. No surprise there, I guess. The upside is this new unit is a little more powerful. <grin>

- The GOOD news is the 18+18' coax combo worked! SWR is now a little over 1 on channels 1-40. Woohoo!

js.