The best and easist way to tune swrs.

TNspeedy said he had 2 francis. can you set them up for duals or do you need to have both with a tunable tip?

 

Yes they can be setup for duals. You tune them with a hacksaw.

Or you can tune them (somewhat) with the length of the coax and type of coax you use.

The package has some coax specs etc on it and if you follow th specs for length and type of coax then you will see exceptable SWRs which will nto harm your radio. They may not b the best for performance but they will be exceptable.

Don't ever fall into the "Factory Pretuned" advertisments as there is no such thing or way they can factory pretune and antenna for the vehical they are going on. Each vehical has differences such as the amount of metal needed for ground plane and hwo they reflect signal etc.

A perfect example would be the antennas I mounted on the previous truck. It was an 01 Volvo VNL 670 with a condo style sleeper. I got the antennas tuned to a near perfect 1.1:1 SWR. I was then moved to a 04 379 Peterbilt. The SWRs were over 2 with the same radio and antennas etc. I had to retune the antennas for the new truck. Shorter sleeper, less fiberglass in the body (more metal) and the exhaust stacks were close to the antenna were the Volvo had 1 stack behind the cab. I also had to bull horn the antennas (never more then 10 degrees) so that they did not flex so close to the stacks when rolling down the road into the wind.

 

while i have heard this many a times, i tend to disagree respectfully, and from experience. i dont use firesticks, but on their page they say that they have sucessfully gotten the dual antennas to work on vehicles with only 5' seperation between antennas on multiple occasions.

i run dual wilson silverloads, on a little s-10 guy.... i have tried so many different antennas, before i went dual, i had one antenna on the passenger side, then decided to say "what the heck" and try two... i did and noticed better performance with most antennas i have tried. (yes i tune all my SWR's low at max 1.3 or lower)

so even though i have heard this, i wouldent say its always the case.

 

[FONT=Arial, Helvetica, sans-serif] Radiation Pattern of Mobile Antennas[/FONT]
[FONT=Arial, Helvetica, sans-serif] Most people think that antennas mounted on vehicles are omnidirectional. This is mostly true, but the radiation pattern is influenced greatly by the body of the vehicle. Remember we stated that the body acts as the "radials" for the antenna? Well, we know that the body does not extend around the base on the antenna equally. Figure 2 shows how the radiation pattern of a whip is influenced by the body of the vehicle. As you can see, the shape of the pattern depends on where you mount the antenna. The pattern is "pulled" to areas where there is the most vehicle body. The pattern is the worst in directions where there is no metal body for a radial. [/FONT]
[FONT=Arial, Helvetica, sans-serif] [/FONT]
[FONT=Arial, Helvetica, sans-serif] Figure 2 - The dashed line shows a omnidirectional pattern you would expect from a mobile antenna, but as you can see, the pattern gets distorted from the car body not being even around the base of the antenna. This is why you should try to mount the antenna as close to the center of the vehicle as possible unless you desire a pattern that stresses a certain direction. Do not think of this as gain in a certain direction, this effect is actually detrimental to the overall effiencieny of the antenna. [/FONT]
[FONT=Arial, Helvetica, sans-serif] Co-Phasing Your Mobile Antennas ("Twin Truckers") [/FONT]
[FONT=Arial, Helvetica, sans-serif] Co-Phasing antennas simply means taking two identical antennas, mounting them on the vehicle and feeding them in-phase. One of the biggest misconception of radio operators is what kind of effect this has on the radiation pattern. Most people think that after you Co-Phase two mobile antennas, your signal will be strongest in line with the vehicle body (meaning the signal is strongest down the road straight in front of you and straight behind you also. This is the theoretical effect that you would get from co-phasing two omnidirectional antennas. However, to realize this effect you need to satisfy a couple of requirements. For one, a good earth ground with long (over a wavelength or so) radial wires is required. Secondly, at CB frequencies the closest you would be able to place these antennas are about 18 feet apart. Since it is impossible to satisfy these requirements, the effect of co-phasing is seriously diminished. Unfortunately, even the "Radio Shack Antenna Book" states that co-phasing two mobile antennas will produce a two directional signal. [/FONT]
[FONT=Arial, Helvetica, sans-serif] So then, is there any advantage to co-phasing two mobile antennas? Why yes, there is. Before we noted that the radiation pattern of a single antenna is "pulled" where there is the most metal vehicle body. You can see the pattern is not perfectly omnidirectional like we would expect it be. As we travel down the road, you will notice signal fade ("flutter" or "waver") from this uneven radiation pattern. Co-phasing two antennas will even out the pattern irregularities. Instead of making the pattern more two directional, it will make it more omnidirectional. Do not expect more "gain" from two antennas. Figure 3 shows how co-phased antennas clean up the radiation pattern. Read the section "Co-Phasing" for instructions on how to make a harness to feed your co-phased antennas. It best to get them as far apart as possible. The best way would be to mount one on the front bumper in the center and one on the back bumper in the center also. Most people think this looks silly (me included!) and mount one on each side of the vehicle. [/FONT]
[FONT=Arial, Helvetica, sans-serif] [/FONT]
[FONT=Arial, Helvetica, sans-serif] Figure 3 - Radiation pattern of Co-Phased antennas. The pattern is now more consistent in every direction, and is less influenced by the body of the vehicle. [/FONT]

 

francis with 18' of quality cophased coax will normally have acceptable swr if mounted properly.i prefer a francis over anything if i am running no amp.i can't stand firestick i have had trouble with them breaking.wilson is a good choice.

 

I hope this is the right place for this, i bought a new truck took my radio, coax, and ant out of international and installed in new KW. in old truck if i could hear you i could talk back, in KW it just talk's fair. SWR is almost the same, less than 1.5. wilson 5000 cophase. int has alum cab KW has fiberglass, stacks in rear of sleeper in int in front on KW. both mounted on mirroir bracket about the same width apart. ran ground to metal on cab frame and to battery. thanks for any help, would like to have my fire in my wire back

 

That is exactly what I was told, that two antenna's will work but not as well, overall, as one. Due to the fact that they are too close together, even in a big Freightliner like I drive. I also have been educated to the believe that the single is better on the driverside due to the fact that that is where all the traffic is for the most part. Truckers are more often, than not, in the right lane, with all other traffic on their left.