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High SWR on CB radio? Answered

I've had a long, hard journey to try and get my Cobra CB to transmit properly. Let me explain.

My radio never has been able to transmit properly, and my friends with their CBs (they have the same kind as me, and their SWRs are fine) can't even hear what I am saying if we are parked right next to each other. This is very surprising, because I have a 4 foot long Firestik antenna. 
So I borrowed my friend's SWR meter and measured my SWR. I have well over 3 in all channels, which is WAY in the red.
I immediately printed out Firestik's high SWR troubleshooting tips, and did everything it told me to do. I tried tuning the antenna as usual, I tried checking all the grounds and connections, and even changing antenna positions. Nothing helps at all. I was still in the red, and my friends could not hear me.
I thought that maybe my antenna or coaxial cable was at fault, so I borrowed my friend's working magnetic-mount antenna to try it out. With the different antenna, my SWR was worse.
Finally, I decided to just get a new radio, because maybe mine had a fried resistor or something. So i took my CB back to walmart, and successfully exchanged it for a brand new radio (without receipt or original box, for that matter).
And just my luck, the new radio STILL has a super high SWR, in the red, the same place as before.

I am all out of ideas. I have searched the many CB and off-roader forums on the all-knowing google, and nothing helps.
Does anyone have ANY ideas on what I can do?



Best Answer 3 years ago

Hi, I know this is now a couple of months old but it sounds like a short to me. Try testing continuity between both the hot and ground wires. Easiest way to test is use a multi meter and put one end on the outside of the screw connection and one on the connection pin (the connector that goes into the radios aerial port). If this is the case make sure the insulation washer isn't broken or that the hot connector is not earthing out via the thread or backing plate. You can put a small amount of insulation tape on the thread which passes through or touches the body. Hope this helps.

I have a 2006 Hyundai Elantra and if I put my mag. mount antenna on the roof of the car and I get less than a 1.5 SWR which is great. BUT when I put it on the trunk I get a 4 on all 40 channels, I know the trunk is metal because the magnet mount sticks to it so it has to be the washers that go on the bolts on the braces that hold the trunk on or the bolts that connect the braces to the car body. Either way, something in that line is not metal and thus not grounded, could be what your problem is - something is not metal and not grounded.

1. Test your radio on a known working system to eliminate the actual radio.

2. If the SWR is still high then you have either a meter problem or a radio problem.

3. If the reading is normal then you have an Antenna issue.

In general SWR issues are created by the antenna and its associated system, the coax cable or the connectors. You can really only fault find by substitutuin.

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Sounds like he did 1.) and he tried another antenna , and another radio and STILL a high SWR. Dragging RF theory from the dark recesses of my brain to which it was consigned, high SWR can blow your transmitter, which it doesn't seem to have done.

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Id try putting your radio in the friends car to determine if your mounting or aerial/ cable is a problem.

Otherwise put the entire system on the bench with a 12v dc supply, or battery if no psu is available, and then try looking for the fault, if its still on.

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SWR is affected by where the antenna is mounted on the vehicle, by proximity of the antenna element to metallic vehicle body parts, or if the antenna is mounted on a Fiberglas or other non-metallic body part. For example, if mounted on a bumper with the antenna element running parallel and close to body panels, SWR will be high. To see the effect, hook a bungee cord or large rubber band near the top of the antenna, hold the other end of the bungee cord and pull the antenna away from the vehicle body while a helper keys the transmitter and watches the SWR meter. SWR should drop noticeably. Mobile antennae use the vehicle as a ground plane which is essentially half of the antenna system. So if the antenna is mounted on a non-metallic body panel, part of the antenna is effectively missing, resulting in high SWR. Most efficient location for a mobile antenna is centered on the roof or trunk lid (unless it is a Fiberglas body, then you need an antenna designed for that application).

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