SWR Tuning on a 102 " whip

[WNY964x4]

i am getting a 102" Stainless steel whip , and for right now i am mounting it inside my bed , later to be mounted on a custom rear bumper , and i was wondering how you tune one of these antenna , i used to have a dual Astatic setup , and they talked about trimming the wire at the top of the antenna's , but how do you tune a 102" , i am gonna be running the 102" , RG-8X coax , and a Uniden PC68 Elite radio , thanks in advance for any help

 

[rockwerks]

You cut off the tip of the antenna about 1/8" at a time till it comes into spec

 

[strvger]

x2 go slow. don't want to cut off too much too fast.

 

[Tbmitchell]

you can also do some minor swr adj by shorting the coax but ur best bet is to cut the ant down lil bit at a time

 

[4x4junkie]

Coax length should have very little effect on SWR. If it does have a great effect, you may not have something grounded well (it is a very common myth you have to use a specific length of coax. However all this does is subdue the obvious symptom of a poor ground (high SWR), but does little to restore performance lost to said poor ground).

As for tuning the antenna, like said, trim it. Or if you need to go longer, then adding a spring or some kind of spacer at the bottom can be used. Usually if grounded properly, the SWR on a 102" whip will be under 1.3:1 on all 40 channels. I wouldn't trim it just for that.

 

[WNY964x4]

so basically i should double check it , but it should be good to go right outta the box ?

 

[4x4junkie]

It should be if it's mounted straight to the body structure of the vehicle, yes. However bumper mounting it is far from ideal though. You might think about mounting it on the bed rail maybe, or dead-center behind the cab works well with full-length antennas (or you can use one of those burly triple or quad-magnet mounts and throw it up on the roof).

 

[WNY964x4]

well it may not get mounted to the bumper , i am mounting it to the Right Rear Stake pocket on the inside of the bed , i cannot mout it to the front panel in the center because the truck has a roll bar and my Blue Light is going to be mounted in the center of the roll bar , and it sticks out enough to be almost to the cab when i get done , so the antenna is toging to get mounted to either the front or rear right side stake pocket incide the bed , pictures of my idea

rear stake pocket

front pocket

tool box mount

 

[4x4junkie]

That should work OK. You'll find your radiation pattern will be somewhat directional off the diagonally-opposite front corner if you mount it in the rear, but probably not enough that it won't work at all in the other direction.

Didn't know you had a rollbar... Can you put the antenna up on the rollbar itself? That would be the perfect ideal spot (that's where I have mine).

 

[WNY964x4]

center mount is out of the question because ot the light , unless i weld some angle under the two mount bars and bolt the antenna mout to the angle

the green would be the angle steel stock

 

[strvger]

adding 102+ inches (mount, spring, etc.) to that rollbar, be careful what you drive under! wouldn't be surprised if even some telephone/electrical wires, and tree branches for sure will hang lower than your antenna will be. you can get a 'quick disconnect' for it when you need to take it down in a hurry. i have those on my antennas. just a thought.

 

[WNY964x4]

That should work OK. You'll find your radiation pattern will be somewhat directional off the diagonally-opposite front corner if you mount it in the rear, but probably not enough that it won't work at all in the other direction.
Didn't know you had a rollbar... Can you put the antenna up on the rollbar itself? That would be the perfect ideal spot (that's where I have mine).

can you explain this to me , i have a hard time understanding how it can favor one corner or another , doesnt it radiate in all directions equally moving from the antenna as the center point , i mean , that is how i would understand it to tork , maybe i am missing something here

 

[4x4junkie]

maybe i am missing something here

Yes, the ground plane (your vehicle body).
Your transmitted energy tends to favor the side of the antenna that has a ground plane under it. This is why mounting an antenna dead-center on the vehicle is best, it gives you more of an omnidirectional range.

I have a 96" Francis antenna on my Ranger's rollbar. I can't recall it ever hitting electrical wires, but trees are very common. Even if it did hit an electrical wire, any wire hanging low enough for it to hit wouldn't be a high-tension (super-high voltage) wire (nothing that your tires wouldn't be able to insulate against). I guess if you were to park underneath some wires, just verify it isn't touching before you put your foot on the ground to step out

 

[WNY964x4]

Right now my main concer is ease of install , with the mount right behind my blue light , it is gonna be a little bit of a pain in the a** to make the bracke and what not , if i do install this at the RR corner of the bed , will i notice a major change in my Range to send/recieve from ahead of me , i do alot of highway traveling , so this is my way of knowing what is coming up ahead of me.

i know my dad had a 102" mounted to the RR corner of his bravada , and my uncke was picking him up at his house 16 miles behind us

 

[4x4junkie]

It's often enough to be noticeable, but it won't prevent you from talking out several miles (especially to a fixed station).
Where you'll notice it the most is if for example you leave the house to go to the store or something, your signal won't be as strong as when you're turned around on your way back home, or in mobile-to-mobile communications where you have a bit of distance between you.