Question:
I've always run one antenna, one coax. I was looking thru WalCott CB shop online last nite, wanting to buy another Wilson 2000 so I have matching ones and noticed the description said something about the coax or antennas being Co-phased. First off, what does that mean and If I bought another antenna, is this cophasing, something I can do myself, or should I take it to a CB shop??
I want maximum performance, so I'd rather some professional do it than me.
Also...are those Wilson antenna mirror mounts any different than a normal mirror mount?
Any comments?

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Co-Phasing is where the coax is equal for both pieces in swr and ohms electriclely and in length for the freq you are using.
From the PL259 plug to the antenna end.
A co- Phase harness is a piece that goes from our radio and splits off to two ends , one for each antenna.
You can make it or better yet just buy one already made and factory soldered ends.
You want better preformance stay with a single antenna. especially if mounted on the drivers side
Your radio is putting out 8 watts lets say. with a single antenna. if you install a second antenna you will have only 4 watts from ea antenna. .
NOW your signal is elecpticle and you are getting out better. If you use 2 you will effectivly cut your distance on transmit. and quite possibly on recieve too.
You can put the second antenna on but not hook it up if you are wanting to look good or uniform.
Most drivers want 2 antennas because it looks good, and some think they actually get out beter, not so.

Answer:

Co-phasing is the act of incorporating more than one antenna into a system to be used simultaneously. The benefit of doing so is to modify your radiation pattern such that it is concentrated in a particular, advantageous direction.
On most vehicles, a single antenna generally provides a uni-directional pattern. It's best range will be in the direction where there is the most metal the antenna can see. ie. If the antenna is mounted on the rear bumper, the best range will be towards the front of the vehicle. The rear will be a dead spot.
On a car's passenger side mirror, the usual best range is had to the driver's side with diminishing results moving towards the front & rear of the cab. Anything off to the passenger side will be a dead spot.
The purpose of co-phasing is to allow a second, active, antenna on the other side of the cab. This provides a pattern modification that provides coverages to the passenger side as well as the drivers side areas.
The resulting pattern is more omni-directional using a co-phase setup. There are places / locations in the resulting pattern that will cause a small gain in range to be noticed over what one antenna alone could provide.
I wouldn't count on this gain as it is difficult to reliably predict in what direction it will occur. Too many variables involved. With carefull manipulation of antenna mounting, grounding & cable length, you can "move" the pattern around the vehicle to a small degree. Sometimes this can provide gain over what one antenna can provide.
The "gain" comes at the expense of radiation in another direction. There's no free lunch here. If you want the best range in one or two directions then you sacrifice it in others.
Where Nite Star left off was that the co-phasing harness / cable needs to be made of 75ohm cable. Virtually the same stuff your cable tv lines are made of. And, the lengths of each line not only need to be the same (usually) but need to be a certain length. These specific lines and lengths provide a proper swr and pattern for a given antenna placement.
What he said about cutting the power in half to each antenna is true. However, there will be gain in certain directions as the pattern of each antenna merges in an additive way. This gain will not be more than 3db typically which is the equivilent of doubling your power. So, in some favored directions you will not have lost the power and in others you will have.
Dual antennas are a trade off between omni-directional coverage and the amount of signal energy you place in the omni pattern. The more you spread out the coverage, the less signal you can put into that coverage.
With a single antenna, you loose coverage on one side of the vehicle but now you have the radios full power to put into the favored side. You aren't loosing half your power to feed the other antenna thru the co-phasing harness.
Personally, I like to keep the antenna centered on the passenger side, I prefer to push my pattern to the front / rear and across the median.
There's numerous antenna / cable geometries to get the pattern you want but it takes time, tools & experience to set up the fancier systems correctly.
I like the KISS principle myself. I rarely see a truly large benefit in fancy systems over a single antenna. Since I'm inherently lazy & since theres no one out there I really wanna talk to that far away, I go with the antenna that looks like it will withstand the physical rigors of car life. I hate having to change antennas because the wind or a small branch broke it.
Go with the longest antenna you can get away with. The more metal in the air, the better will be the range and swr. Shortened antennas are a trade off. They are only attempting to mimic the performance of a true, 9 foot, quarter wave whip.
Make for a good ground system. That's the other half of the antenna performance issue.
Are ya still awake?
bc

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Wow! And to think.....I always thought....bolt her up there and press the talk button!
I think I'll stick with one antenna. When I buy the extra antenna and extra mounting bracket "just for looks" would get kinda pricey. We'll see.
What would you recommend I do. I've had the antenna centered on the drivers side, with my Cobra 29 NWSTWX. I think I have the longer of the two Wilson 2000 whip sizes offered.


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Explain how you "push your pattern" to the front/rear and across the median.
M

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Hywayjunky, here's what some drivers have been doing when they want the "uniform dual antenna look".....
They mount two antennas, but use a single antenna for their CB (as I've had the best luck with myself). The other antenna is connected to either a second CB, or makes a great AM/FM antenna (I've tried it before, and even with fiberglass antennas, it works pretty damn good! If you listen to AM, be sure to run a ground wire from the antenna mount to the cab ).
If you are in a company car, you're still best using your own coax cable anyway, as the factory coax cable in the car is likely of inferior quality. Most every reputable CB shop out there will advise against using the factory coax in the car.
Good Luck!

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Recall where I wrote how the pattern is changed or skewed by the metal in close proximity to the antenna.
If your roofline is metal, the antenna will see it and make the pattern directional towards the greatest amount of "nearby" metal. If the antenna is on the drivers side, the pattern will be directed towards the passenger side and to a diminishing degree towards the front and rear.
"Pushing" the pattern is a bit of a misnomer. I used that term to say I mount my antenna on the passenger side to take advantage of the fact that my "reflector", the greatest amount of roof metal, will cause my signal to radiate towards the drivers side which means it will be directed toward the other side of the hiway.
Visualize looking straight down on your car. The ideal pattern will look like the letter O with the car in the middle.
If the antenna is on the passenger side, the O will look more like a backwards D with the flat side on the passenger side.
I know this isn't the best way to say it but thats all I could come up with this late. Sorry

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best range will be in the direction in which the longest path of body or frame metal exists. on the drivers side with a single antenna the two strongest lobes would be off of the passenger rear corner and the passenger front corner of the tractor trailer. great if you drive in the UK. with a single antenna on the passenger side the two strongest signals would be off of the drivers rear corner and the drivers front corner of the car. great if you drive in the USA. even better if every driver mounted a single antenna on the passenger side of the car.
it is of no concern to anyone that the transmitter power is divided between two antennas because the power is re-combined via the interfering patterns of the two antennas. this "interference" can take two forms, either constructive or destructive. we want "constructive interference."
due to the physical geometry of a tractor-trailer rig, 1/4 wave spacing of dual antennas for improved performance over a single antenna is not mandatory. with a pair of antennas at 1/8 wave spacing over a uniform ground plane surface the pattern generated would normally be omnidirectional but this is not the case because of the non-uniform ground plane presented by a tractor -trailer rig. the rectangular shape works to maintain an increase in signal strength towards the front and rear of the rig, even down to 1/8 wave spacing, given the proper antennas and the correct type and lengths of feedline for the phasing harness.
what's possible? let me answer the question by asking another. what's the distance in miles from San Diego to Riverside?

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With a tractor and a trailer attached, would be the effect of the trailer? Does this skew or change the pattern any? Does it reflect more "forward with the duals since the trailer is lots of metal and sort of "in the way". What happens if you deliberately ground out one of the two antennas? Is there any reflection present? Just asking for the sake of conversation.
RR

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Creates pattern skewing with unpredicable results depending on trailer characteristics.

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A lot depends on how much rf is actually being radiated in that rearward direction to start with. Most times not much. The trailer is almost too far away to be a usefull contributor although it will definately have an effect on the pattern. Most likely it acts as a shield for the most part.

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Gounding one antenna located in the very near proximity of another (within a half wavelength or so) will cause the grounded antenna to act as a parasitic element. It will absorb power & reradiate it. If the grounded antenna is tuned 5% higher in frequency, it will act as a director just like an element of a beam. If it's tuned 5% lower in freq, the element will act as a reflector. If it's tuned at the operating freq, it will simply absorb power and dissipate most of it to ground.

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"The trailer is almost too far away to be a usefull contributor although it will definately have an effect on the pattern. Most likely it acts as a shield for the most part."
the further away the nose of the trailer from the mirrors the better. it also depends on how high up the antenna the base of the loading coil is located. if we look at a straight line with a 20+ degree angle above horizontal starting at the base of the loading coil and move towards the nose of the trailer either one of two things will occur. the line moving away from the base of the loading coil will impact the front nose of the trailer or it will pass over the top of the trailer. if we can get it over the top of the trailer with the trailer roof underneath it, we can increase the amount of signal available off the back of the trailer. the two easiest ways to do this is to move the antennas further forward away from the nose of the trailer or raise the height of the loading coils, either by adding a longer shaft or selecting a different antenna design. under these conditions the signal off of the back of the trailer can be 30 - 40 % more intense than the signal to the front and is much less "skewed" and more "uniform" than you would imagine. relatively speaking, if the base of the loading coil is not high enough to deliver any low angle radiation above the top of the trailer then the back of the rig remains "dead" when referenced to the signal produced to the front.
co-phasing or phased array:
a group (2 or more) of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction (or directions) and suppressed in undesired directions.
The relative amplitudes of--and constructive and destructive interference effects among--the signals radiated by the individual antennas determine the effective radiation pattern of the array. A phased array for our discussion is used to direct a fixed radiation pattern. for the purpose of the over-the-road car driver, the most useful directions with relationship to the position of the tractor-trailer rig would be to the front and the rear of the rig, a bi-directional pattern being the most desirable, perpendicular to the plane of the array.

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I can't imagine how you guys come up with this stuff. Who are you...NASA? What launch?
Wow! I'm sure glad you understand all that antenna stuff. It'll save me a few thousand dollars in buying some ridiculous EESoft modeling software.

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Co-phased is when Kirk and Spock (or Picard and Worf) both turn their phasers on you...
I'm sorry, I haven't been well since the surgery. I'll go quietly...