High swr reading

[ajcardona27]

I have high swrs and have tried everything to fix it any suggestions? I’m running dual sirio bull trucker antennas which are on each side of a headache rack that’s on my truck bed(the bed is composite) I have replaced the the dual coax cable and adapters and same issue. I even ran a ground wire to each adapter. Could my antennas just be junk?

 

[nomadradio]

(the bed is composite)

There's your problem.

Those antennas require a RF ground. Not the same as a skinny wire that grounds your headlight bulb.

The ideal RF ground would be the metal roof of the vehicle, in a mount near the center. Plenty of surface area around the base of the antenna.

The farther the antenna's feedpoint gets from that metal surface area, the higher the SWR.

If you were to ground the rack to body metal at BOTH ends, this might help. The shorter the connection, the better.

I'm pretty sure an antenna analyzer would reveal an insufficient RF ground for those antennas.

Consider for a moment how well (poorly) each of those antennas would work if you stepped away from the truck, holding the base of the antenna in your fist. The SWR would go sky high, for lack of a proper RF ground.

Years ago, Antenna Specialist sold a ground plane kit for fiberglass surfaces. It was a roll of aluminum-foil tape. You plastered the inside surface of the fiberglass roof, tonneau or boat and connected the feedpoint ground to the foil.

It worked okay the couple of times we tried it, but this probably isn't much help with your setup.

Somebody (else) needs to come up with a true no-ground mobile antenna that doesn't end up using the radio for its ground. They give you less and less metal to work with each succeeding model year.

73

 

[Eldorado828]

They give you less and less metal to work with each succeeding model year.

We fight it more and more on class 8 trucks. I cringe a radio install when the time nears of getting in a new rig.

 

[ajcardona27]

There's your problem.

Those antennas require a RF ground. Not the same as a skinny wire that grounds your headlight bulb.

The ideal RF ground would be the metal roof of the vehicle, in a mount near the center. Plenty of surface area around the base of the antenna.

The farther the antenna's feedpoint gets from that metal surface area, the higher the SWR.

If you were to ground the rack to body metal at BOTH ends, this might help. The shorter the connection, the better.

I'm pretty sure an antenna analyzer would reveal an insufficient RF ground for those antennas.

Consider for a moment how well (poorly) each of those antennas would work if you stepped away from the truck, holding the base of the antenna in your fist. The SWR would go sky high, for lack of a proper RF ground.

Years ago, Antenna Specialist sold a ground plane kit for fiberglass surfaces. It was a roll of aluminum-foil tape. You plastered the inside surface of the fiberglass roof, tonneau or boat and connected the feedpoint ground to the foil.

It worked okay the couple of times we tried it, but this probably isn't much help with your setup.

Somebody (else) needs to come up with a true no-ground mobile antenna that doesn't end up using the radio for its ground. They give you less and less metal to work with each succeeding model year.

73

This is the setup. Does the rack being steel not help it ground at all? The ground wire for each are going to the frame

 

[Eldorado828]

View attachment 68024
This is the setup. Does the rack being steel not help it ground at all? The ground wire for each are going to the frame

Is that not a steel bed with a composite shell liner?

I think part of your issue is the loading coils are right next to that rack and creating a lot reflect. Those coils need to be above that rack for starters. A long top loaded antenna will probably work much better in your situation. Firestick fs-5, fs-6 or skipshooters would get that load above that rack.

 

[nomadradio]

He's right. There is a limit to how close you can get metal to those loading coils before it disrupts the coil's tuning. That will drive up SWR. If you don't believe me, wrap your hand around one of those coils and see the SWR change from that alone.

73

 

[Keto]

yep I think that's what's going on the RF is bouncing around off the cab for one thing.
I tried this with one coil antenna the same spot on a F-150 swr was no good and couldn't get it right.
I tried back behind the cab of a Mack, and it drove me nuts trying to figure it out. Open the door and it all changed, swr was all over the meter. Went with a mirror mount and boom, it was good and stable.

 

[G-Golly Wally]

View attachment 68024
This is the setup. Does the rack being steel not help it ground at all? The ground wire for each are going to the frame

Good looking rig. Those taillights look like the same style I just put on my 06 F250. I like the SS102 whip with 6 inch spring, that's the only mobile antenna I can seem to get a low swr on. Others I can get the swr's to an acceptable level for use but if I want 1 to 1 swr reading, I can only seem to do that with the SS 102 with the spring.

 

[Eldorado828]

Well I wonder what the op decided to do?

 

[fourstringburn]

If antenna height isn't an issue, a single antenna is omni directional and easier to tune and coax feed.

It's also better as a mobile because 2 antennas give a front to back hour glass radiation pattern where a weaker side to side signal will occur.

I would run the 1 antenna dead center of the vehicle on the rack.

 

[BC Coyote]

Well I wonder what the op decided to do?

Who knows ! There's a lot of threads that end without us ever knowing how or if a problem was fixed or remedied. People ask for help, receive help, but then we never know the final outcome !
It would be nice if folks dropped back in to the thread to let us know if and how the problem or issue was fixed !
That said, this thread is only a three days old, so the OP may well still be experimenting with a fix, and will let us know the outcome soon enough........