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Help! KJ CB Antennas


 
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MiniDevil
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Joined: 05 Dec 2007
Location: Southeast PA

PostPosted: Wed Dec 05, 2007 1:20 am    Post subject: Help! KJ CB Antennas Reply with quote

Hello,

I am a new member looking to finally mod my Liberty a bit.

I've had my 03 Sport model since February and its proven tough and reliable, despite getting rammed from behind twice within my first 3 months having it Evil or Very Mad.

I am looking to add a mobile CB sytem to it, but the problem arises when I realize I do not know where I can mount dual 4' firestik antennas. The company doing the antenna installation and tuning wants to throw mounts on the hood of my liberty and just have the antennas sticking up.

I was kind of hoping that I could mount one firestik on the rear fender area right behind the plastic wheelwell on each side (behind the fuel tank door basically) and then I could even run a dual 5' antenna setup. Is this possible?

Is there a better way to maximize my RX/TX?
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whlstnd
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Joined: 08 Feb 2007
Location: spfld,il

PostPosted: Wed Dec 05, 2007 5:00 am    Post subject: Reply with quote

y would you want to run a dual setup? it makes the radio very directional. do a single antenna and if you need to talk better you can find a linear(not legal though) to up the wattage and that will gain you alot of distance.
mike
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MiniDevil
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Joined: 05 Dec 2007
Location: Southeast PA

PostPosted: Wed Dec 05, 2007 2:30 pm    Post subject: Reply with quote

I was told that a dual setup would effectively double the range of receive and transmit, whereas a linear would only help transmission, and leave you able to talk far but not hear far... was I misinformed?
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ThePhantum
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Wed Dec 05, 2007 6:36 pm    Post subject: Reply with quote

MiniDevil wrote:
I was told that a dual setup would effectively double the range of receive and transmit, whereas a linear would only help transmission, and leave you able to talk far but not hear far... was I misinformed?

CB reception works the same as receiving AM/FM transmissions (as a matter of fact CB is an FM transmission in the 27Mhz range). Yes, a dual plane setup will help you hear more, but it's much more about the power of the broadcast that you are listening too.

A dual setup will increase the overall range (transmit and receive) in front of and behind the vehicle...but it does this by sacrificing range to the sides. This is what a lot of truckers do since they are mainly interested in talking/hearing other drivers ahead and behind them (and it sounds like you are talking with a shop that mainly does CB installs for truckers). For general use, and especially if you plan to use it on the trail, stick with a single antenna setup. It will give you the best all around performance.

Now, to get the most performance out of a CB system, spend the time and money on the antenna and coax. I've said this many times before...the best radio with a crappy antenna system will NEVER outperform a crappy radio with a good, well tuned antenna system. Think of the antenna system as garden hose. If you have good water pressure (transmit from the radio), all the hose fittings are tight (the antenna mount) and the hose doesn't have any leaks (good coax), you are going to be able to push water pretty far out of the nozzle (antenna). But if the hose has holes in it, or the fittings are leaking, etc., etc., the water will not travel as far out of the nozzle. While you can't see RF energy pouring out of a bad piece of coax (or interference pouring into it), the results are the same....decreased range and performance.

Ideally speaking, you want to have the antenna mounted on the roof at the center point of the vehicle. This allows the transmission power to radiate into unobstructed free space, using the vehicle as a ground plane. Of course, mounting an antenna on the roof is not always practical. So it becomes a trade off of performance versus convenience.

There's a few things to keep in mind in terms of antenna performance, regardless of where it's mounted:
    Stick with a top loaded antenna. They perform better than center loaded or bottom loaded.

    At least two-thirds of the antenna should be above a vehicles roof line. This allows transmit power to radiate as unobstructed as possible.

    Taller antennas perform better than shorter antennas

    Antennas mounted higher on a vehicle perform better than if mounted lower on the vehicle.

Finally...have the system tuned. Low SWR is directly related to system performance...as a matter of fact a high SWR can even damage the radio.

Once you've got a well tuned, quality antenna system, if you connect a decent, well tuned radio you'll be surprised at how well the entire system will perform. My Jeep is not a good example...my antenna is mounted on the roof rack dead center of the vehicle and my radio has had lots of work done to it... but my wifes Jeep has the antenna (4' Firestick) mounted on the rear tire carrier. The radio is a low end Cobra that has been tuned. On a bad day, she can transmit for about a mile and a half. On a good day, she gets out 5 miles.
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MiniDevil
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Joined: 05 Dec 2007
Location: Southeast PA

PostPosted: Wed Dec 05, 2007 7:09 pm    Post subject: Reply with quote

Thank you for your input, very useful knowledge. Perhaps you could help me decide on an antenna setup for my Jeep?

Right now I just want the best antenna setup I can possibly get. I will worry about a radio unit and tuning the unit later.

My main use of the radio will be for highway driving, however I will occasionally use it during offroading and camping.

Would a continuous coil antenna like a FireStik be better than a top loaded antenna, since I drive mostly on the highway? I am not sure of different antenna brands so I do not know whether or not there is a top loaded antenna capable of resisting the wind at highway speeds. Originally I wanted to go with a 6' FireStik, but the shop told me that there would be way too much dancing of the antenna, and that I should stick with a 4' FireStik. They also said I could go with a 2 or 3 antenna setup. The 3 antenna setup kind of threw me off because I'd never heard of it before.

I would like the ability in an emergency situation to be able to transmit 15 miles, as when I go camping it is out of range of everything except a base station about 15 miles away. Not only is the radio going to be used as a means of highway communication, but I want to be able to rely on it in an emergency situation.

As far as practicality for my circumstance goes, it's a bit tough considering I want to be able to convert from highway use to deep offroad use. I just want an antenna system where I can still go under bridges without smacking the antenna off the vehicle Mr. Green
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ThePhantum
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Thu Dec 06, 2007 7:51 am    Post subject: Reply with quote

The first thing is going to be to figure out where to mount the antenna. When picking the location just keep the points listed above in mind. That's really going to be entirely up to you...but if it were me I would figure out how to get it on the roof, at the center point of the vehicle.

IMHO, coax is the most important component. You can have the best antenna in the solar system, but if your coax is a piece of crap the system is going to suck. I run Belden RG8X Mini 8, and would recommend it. When the cable is run, make sure that there are no sharp bends or kinks (think about the garden hose analogy). Now, lot of people will tell you that when used with top loaded antennas, you need to have 18' of cable. I'm not a firm believer in that, mainly because I only run 12' and my system gets out farther than most. However, if you do use 18' and only need say 10' do not wind the excess up in a tight loop. That will become an RF choke. Any surplus should be wound like yarn about 18" long and tied in the center with a plastic wire tie.

The next important component is the antenna mount. It has to both physically support the antenna and act as a electrical bridge between the antenna and the coax to/from the radio. There's a lot of cheap ones out there that use non-stainless steel washers (which will corrode), or that have cheap plastic insulators (which will crack or collapse), etc.

As far as the antenna itself, stick with a top loaded unit that has a tunable tip. Firestiks are decent antennas and will do the job well. They are too rigid for my tastes though, so I prefer flexible antennas. The Everhardt Tiger superflex is a great performer, however it does not have a tunable tip. It needs to be cut to tune it. I run a 4' Wilson superflex. It has a tunable tip and I've whacked it off many a low hanging branch with no adverse affects. It's mounted on the roof of my XJ and even with 6" of lift, I've never hit it on anything going down the highway.

Finally, have the system tuned. This post is already long enough, so I'm not going to get into a discussion on what SWR is...besides quanda71 put it best in his post on adjusting SWR:

quadna71 wrote:
CB and amateur radio systems work best when the antenna system's impedance matches the transmitter's output impedance as closely as possible. The meter's standing wave ratio (SWR) function helps you trim your antenna to the precise length you need for the maximum transmitted power.


Basically, you want that ratio to be 1.5 or less. You can read more about SWR here.

Now, in regards to getting out really far in an emergency situation, I cannot and do not officially recommend any of the following since none of it is legal. It is being posted here for informational purposes only. Radios are set up to deadband so that when you are transmitting on say channel 19, it won't step on channels 18 and 20. You can have the radio modified with a switch that will drop that deadband...in other words, you will get out much further, but will be stepping all over adjacent channels. You can also run linear amps, which will add more power to transmit...more power = more distance. Drop the deadband and flip on the amp and you will get out for miles.
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97 XJ Sport with a bunch of stuff
Quote:
Never argue with idiots, they drag you down to their level and beat you with experience
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MiniDevil
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Joined: 05 Dec 2007
Location: Southeast PA

PostPosted: Fri Dec 07, 2007 12:39 am    Post subject: Reply with quote

Phantum,

Thanks for your help, this is a great help indeed!
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