The best and easist way to tune swrs.

you cannot tune a francis antenna. the only thing you can try to do to get a lower swr is to make sure the antenna is grounded

 

just take them to a good cb shop and they will know what to do, or you can try to ground the antennas yourself.

what exactly is ur swr reading?

 

First off, you don't ground the antennas. You make sure the mount is grounded not the antenna itself.

Second, you can tune the Francis antennas but I don't recomend it. Get some firesticks of Wilson fiberglass with the tuneable tips.

If you are running duals (cophased) then go get a seperate coax for tuning the antennas seperatly. Don't just unhook one of the antennas and use the facotry cophased coax for this. Bad things will happen to your radio.

Take your seperate coax and hook it between the radio and the antenna. Tune the antenna up or down (longer or shorter) till you have the lowest possible SWR. 1-1 is perfect while anything less then 2-1 is exceptable. Once you get one antenna tuned then go do the other one.

Once you have them both tuned to read the same swr then hook the factory cophased coax to the antennas and double check your SWR. If more fine tuning is needed then you must tune both antennas at the same time meaning that if you shorten one 1/8 of an inch them you have to shorten the other 1/8 of an inch.

If you are having problems getting th SWR down to an exceptable level then check the grounding system out on the mounts. Also make sure that the antennas themselves are not grounding out. I have lost count of how many times I have found the plastic washer on some mounts missing which causes the antenna itself to ground out.

But the threaded section were the coax hooks to the bottom of the antenna mount should be properly grounded while the center section of the coax mount should not have continuity to ground.

 

that your problem there . using 3 sections of regular 50 ohm coax with a T coupler . you need a dual antenna harness made from 75 ohm coax .
tuning seperately as rat said is ok for a ball park to maybe even close enough tuning . if you havnt or cant do it yourself then get someone to do it for you and watch so you can do it later yourself if the you need to .

turn your mic gain all the way down when setting the swr .

 

What do you mean close enough? Not to start an arguement but the proper way to tune a dual setup is to tune each one seperately as I described.

Tune each antenna seperately using a seperate 50 ohm coax then hook them up to the cophased coax and fine tune them both at the same time.

Mine are tuned to a 1.1-1. The SWRs do not change when I add more power such as going from my Cobra 29 to my high powered Connx 4300.


But no you can not use two 50 ohm coax on a dual setup. You must use two 75ohm coax.

If the big truck came setup with dual antennas and you plan on using the stock coax then you need to stick with duals or run a seperate coax for a single setup.

If you ar going to run a single setup then placing the antenna on the passenger side is perfered because your ground plane gives you a better pattern to the drivers side. Just make sure the antennas are long enough so that over 2/3 of the antenna are above the roof line or unobstructed by the cab or you will have some serious reflect problems and poor performance.

 

no offense taken rat . you are right . apparently i wasnt paying enough attention to what i was typing .

im not a truck driver but i do have a question .
since mounting a single antenna on either side will favor tx and rx to the opposite side and since the vehicle is always moving and in different directions i dont understand favoring txing twoards the drivers side ?
it seems to me mounting on the drivers side would be better simply because theres typically less or no trees to hit on the drivers side and potientally dammage the antenna system .

 

The best place for an antenna would be, ideally, in the center of the vehicle. However, taking into consideration the trees you mentioned, mounting your antenna would be best mounted to the left. So-called "co-phased" antennas, popular with CB, do little or nothing for small vehicles such as cars or pickup trucks. When less that 9 feet apart, they are now OUT of "phase" and are in their own near field, negating any advantage. Dual antennas for CB (big truck are an exception) do one thing: put extra $$$ in some snake oil salesman's pockets because he can sell TWO antennas instead of ONE!

Gadfly