One thing to try if your SWR goes up with higher power would be a low pass filter. Reason being that the closer you get to the max power a radio (or amp) is capable of transmitting at the more harmonics it will produce, and with these harmonics being on frequencies other than the one your antenna is tuned for they will get reflected back to the radio. This is quite often (but not allways) the reason for SWR readings that change with power levels. To check this out get a good quality low pass filter and take two power measurements with the equipment hooked in line as follows.

reading #1:
radio->amp (if being used)->power meter->antenna

reading #2:
radio->amp (if being used)->filter->power meter->antenna

While there will allways be an insertion loss when a new piece of equipment is added in line this will be allmost unnoticeable with a good quality filter, and most of any difference in power measurements will probably be due to harmonics.

 

1:1 is the baseline to strive for. You'll never get that, but it's fun to try. If your equipment does show 1:1, it's because the equipment isn't accurate enough. The best I've ever achieved on a match is 1.12:1 using Anritzu and Bird analyzers that cost about $8 grand a piece. And that was on a real narrow part of the band. The 0.5:1 was just tech shorthand, "I got .5 in the middle and that's the best I can do." 1.5:1 is a great number for a twin array and if he did it for $85, that's not bad.

You have to watch out for some shops. It's real easy to cut the coax going to one of the antennas. It's hard to blame them though. Tuning a phased array at a CB shop, when all they have for equipment is a Watt meter, O-scope and MFJ antenna meter must be a nightmare. If you have a dual channel scope, you can measure the current going though each coax with ferrites, (basically, you are making your own custom clamp meter).

Running twin sticks at less than 1/4 spacing, (like on our pickups), gives an omni pattern just about like a single. But twin sticks rate about a 9 for cool factor, so why not? If you do have a big truck and can get the 8-9 foot spacing, it won't quite double your gain, but that coupled with the increased antenna height might.

Some of the truckers here have a pretty good grasp of how this stuff works.Try doing a GIS for, "small magnetic loop transmit antennas". It's a far more mechanical antenna and you use a capacitor to tune, instead of a coil. (You can make your own.) It's physically small, with a very high Q, (very narrow bandwidth for both Tx and Rx), and directional. It would easily fit up under the fiberglass wind deflector and no one would even know you had a CB - until you keyed up.

 

When tuneing dual antennas I usually hook one antenna to the co-phase harness and put a dummy load on the other lead from the harness, then I tune that one antenna. Once the first antenna is tuned I remove the dummy load and hook up and tune the second antenna, while doing this the first antenna is still hooked up but I don't touch the adjustment on it. I know that this isn't the best way to tune dual antennas but with only a standard SWR meter and a cheap dummy load you can get it pretty good with a minimum of time and hassle. Of course your milage may vary.

And as far as talking across the median is concerned you have to adjust your clarifier/delta tune to compensate for the doppler effect

 

I have a Uniden PC68XL (I think thats what it is) mounted on my ceiling, a 18' dual coax, and dual 4 1/2' Hot Rods on each side of my toolbox. There is no way to tune them, the CB doesnt have SWR and there is no adjustment on the antenas. My CB transmits and recieves further than most others I know around here who have a single antena. It'll transmit and recieve better than the Cobra Nightwatch with dual 3' antenas in my Dad's KW (mirror mount). I do not understand why it works this good, it isnt anything special. People usually think i'm miles closer to them than I really am. I've been thinking about moving the antenas to my mirrors (I have the big west coast big rig style ones) to see if that'll make it any better, but then they have a better chance of getting whacked off (No pun intended)

 

The nice thing about gain antennas is that the gain works for receive as well as transmit. Some of you are really close to understanding how this stuff works, some of you know it and I'm always learning.

A single whip system is pretty easy to understand. You have your radio with a connector on the back with positive in the center and negative on the outside. You hook up the coax from the radio to the antenna, where the whip is the positive and the truck is the negative. Since this is AC both sides get used. This is just an AC circuit. The signal off the antenna radiates out and some of it is absorbed by your truck, some of it just goes out and some of it bounces off your truck and combines with the signal just leaving the antenna. Partially, it's these combined signals that we try to deal with when we tune for SWR. We want the positive side to equal the negative side and look like a 50 ohm load to the radio.

The wave leaving your radio is about 36 feet tall. You only need half that height, (18 feet) for the positive side. When you draw a wave form, you start with a horizontal line and then draw a sideways "S" on that line. Anything above the line is positive and below is negative, (you get the picure). Think of where you mount your antenna as the horizontal line. The negative part of the 36' wave from the radio is going to your truck, the positive side, (18 feet), is going to your antenna. The highest point of the positive side is about 9 feet and it's at this point the most signal is out there. That's why the 9 foot SS whip works so well. The signal comes out pure, reacts with the ground plane and radiates out fairly horizonal.

The whip also smacks everything you drive under.

We can trick the wave by wrapping a 9 foot antenna around a short fiberglass rod and make it think it still 9 foot tall. It still looks the same to your radio, but what happens when it comes out the positive side of your antenna and combines with the negative side of your truck is much different. The strongest part of your signal tends to bounce up, instead of out. This is ground plane. No matter what you do with the short whip, this is what happens. But enough signal gets out low enough to use your radio. As far as your radio is concerned, by tuning for SWR it can't tell the difference between the full size 9 foot and the short 9 foot, but wave can after it leaves your antenna.


When we go to twin whip what we are doing is trying to force the signals together and go a certain way. As far as your coax goes, it's kind of like wiring up two legs of 120V to make a 240V circuit. The two phases add together. If one of the phases were off, you might get 170V from the waves partially cancelling out. (This doesn't happen under normally.)

Same thing on the phasing harness of the twin whip. Even though the physical length of both coax might be 9 feet, the electrical length might be different. The signals are in phase when they split, but migh be different when they get to the antennas. Fordpickup460 probably has a matched phasing harness. Just like tuning motorcycle carbs, you have to be able to see both sides at the same time to tune. It's hard to do, but sometimes you luck out.

If you've followed up to this point, you've seen how the positive side of your antenna and the negative side of your truck, (ground plane) work together to point your signal. Adding the extra stick is just helps point. We still have to work with that big wave though. When you install the sticks close together with both signals in phase, the wave thinks it's shooting out of one antenna - there's not enough room for the signals to combine off each other.

At about 4' separation the gain is around 0.3dB, about the same as a single whip. As you spread the whips apart the gain will increase, so you tune the gain by spreading the antennas. At about 9 feet the gain is around 2dB. If you were to spread the whips as far as they would go with the 18 foot coax, you would more than double the gain front and back, which doubles the power of both receive and transmit inline with your truck. Then broadcast how you took out mailboxes on bothsides of the stree in a single pass.

Twin whips look really cool though and they do help a little, but it's not a magic fix. You not only have to tune for gound plane and impedance, but tune the phasing harness - when the most you can hope for is a third more gain.

 

I have the same CB. I dont have a whip for it...but I do have a 3' magnet mount antenna that I use (used. I dont have it hooked up in my truck yet. Im wanting to get a whip).

I get awesome signal with it. Better than my friends who use a 102" whip, and a Wilson 6' whip. I would sit at school in the morning and listen to the truckers talk on the interstate 10 miles away just as clear as if they were sitting next to me.

I hope a new antenna wont screw that up

 

Umm... I have a VHF radio with a 3' mag mount on the roof of my diesel... My 460 truck used to sport a 3' VHF mag mount, and a 5' CB mag mount when I was doing winter road stuff...

 

The Uniden PC68 is a good solid radio. The Cobra radios have a good reputation mostly because the older ones were very good, the newer ones ain't what they used to be.

Here is a good read for anyone looking to find out a little more about antenna theory
http://http://www.signalengineering...._antennas.html

 

Whips with no radios? What's the point? I remember years ago people would put FAKE cell phone antennas on their vehicles. Pretty funny. And again. What's the point??

I had a few ask about the VHF/UHF "ham" antenna on my roof saying "That's too small for a CB antenna. You're not going to get out good with that."

 

Whips with no radios? What's the point? I remember years ago people would put FAKE cell phone antennas on their vehicles. Pretty funny. And again. What's the point??

I had a few ask about the VHF/UHF "ham" antenna on my roof saying "That's too small for a CB antenna. You're not going to get out good with that."

 

Ya this senior at school has a 95 eddie thinks its the nicest truck in the world only drives it about 2 times a month. he has dual whips but no CB i said somethin to him and he gave me no responce. I have dual whips on my 96 F150 (5.8) and they look great. Dont let any one tell you their dumb, if you have a CB you can have them if you dont then you cant. pics in my galery