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PostPosted: Tue Jan 03, 2012 4:00 pm 
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Hello all.

Bought my first CB radio with a 3 foot whip antenna from a nice little thrift store and I have been playing around with it. Hoping to install it in my truck, listening to local channels, etc. I admit I don't know much about CB radios but I know the distance is dependent on line of sight so the taller your antenna the better distance you can get. If I am ever mobile in a PAW situation and I just have my little whip antenna it may be hard to get any decent distance on my signal and carrying around a big tall antenna isn't really possible. First question is how do you (my fellow Zombie Squad CBers) plan on getting reception distance in the PAW?

My idea: A balloon?
What are the practicalities of using a helium balloon to hoist an antenna wire? I've read that CBers have been using balloons for a long time. Can it be a thin wire attached to the end of the whip antenna or do I need to lift the entire antenna and coax cable? I'm thinking if I can just carry a small tank of helium, a heavy duty balloon, and a thin wire on a coil it would be perfect for being mobile. I hope to play with this idea but I'm interested if anyone else has some ideas or advice. Thanks very much for reading, best wishes.

- Joey_Numbers


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PostPosted: Tue Jan 03, 2012 4:25 pm 
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I'm not an expert, but I believe that CB antenna length is a function of its percentage of the frequency wavelength. (Radio experts, please correct as needed.)

Also, my understanding is that a good sized groundplane is also beneficial to transmitting to maximum range. (this is why an antenna mounted square on the roof of your car works better than one mounted on the corner of a fender.)

The rest of the range issue simply comes down to taking full advantage of the maximum allowable transmitting wattage. (Linear amplifiers were quite popular in the 1970's for boosting CB range, but they were illegal then, and still are now...)



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PostPosted: Tue Jan 03, 2012 6:05 pm 
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The people equipped to communicate outside the line of sight can use radio bands and modes where signals bounce off the Earth's ionosphere. The "HF" - high frequency- ham bands, as they're known. You can literally string an antenna out and tie it between two trees . It doesn't have to be high off the ground.

Another way people communicate outside the line of sight is by using repeaters. Yes, technically that's still line of sight but repeaters, remote receivers and other infrastructure is put into place so stations can communicate over relatively long distance.

There's also satellite.

Using a weather balloon to raise an antenna has a fundamental flaw.
That's that power is lost in the coaxial cable. The longer the run of coax, the more power you'll need. And the 4 watts provided by CB's in the US does not go very far. If I'm not mistaken the FCC regs limits CB antenna heights as well.


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PostPosted: Tue Jan 03, 2012 7:47 pm 
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CB radio is not nor has it ever been a long range radio service. mobile to mobile 5 miles, 10-20 miles mobile/base at little more base to base. A bigger antenna isnt going to greatly improve the distances. Yea people can talk 100+ miles with an illegal amp, but not reliability when ever they want. Only when the bands up. If the band conditions are not favorable, no amount of power or antenna will help.


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PostPosted: Tue Jan 03, 2012 7:52 pm 
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The Jinxmedic wrote:
Also, my understanding is that a good sized groundplane is also beneficial to transmitting to maximum range. (this is why an antenna mounted square on the roof of your car works better than one mounted on the corner of a fender.)


The ground plane for a fender mount or roof mount is exactly the same. The entire care is the ground plane. Mount on the roof gives you the most omni direction patter where fender mount tends to put the signal more forward and out from the fender.

The best CB antenna is a 17ft whip mounted in the center of the root. This is hardly practical so EVERY CB antenna is a compromise. being the short distances most people talk. Any antenna over 4ft or so will do fine. The higher the better, but you take what you can get.


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PostPosted: Wed Jan 04, 2012 4:55 am 
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Joey_Numbers wrote:
First question is how do you (my fellow Zombie Squad CBers) plan on getting reception distance in the PAW?

With the limitations of what you can do with/in a car, drive to the top of the tallest thing you can find. Hill, parking garage, overpass, bridge, doesn't really matter. Let the ground become your tower. People talk around the world on milliwatts of power with handheld antennas just by standing on tall things.


Quote:
My idea: A balloon?
What are the practicalities of using a helium balloon to hoist an antenna wire? I've read that CBers have been using balloons for a long time. Can it be a thin wire attached to the end of the whip antenna or do I need to lift the entire antenna and coax cable? I'm thinking if I can just carry a small tank of helium, a heavy duty balloon, and a thin wire on a coil it would be perfect for being mobile.

Basically not going to work unless you scale the idea waaaaaay up. Let's say you wanted to put the ballon up 200' for better LOS. Wind is going to take it down range, so the "string" holding the balloon will be MUCH longer than 200' to get the ballon 200' in the air. Assuming the actual angle of the string is 45* relative to the ground, the actual string length will be almost 300'. Since the line will sag in a catenary curve, it'll be even longer than this in reality, but I don't feel like calculating that. Now, conveying a 27MHz signal through 300' of wire is no small challenge. You'll have to use a cable with high efficiency such as LMR-400. LMR-400 is 0.20lbf/ft. That's 60lbs of feedline. So your ballon is going to need to be HUGE to just lift the weight of the feedline. Then you have to add the weight of the antenna. Your best bet with a ballon mounted antenna is going to be a vertical wire dipole. How exactly you're going to feed the dipole in the center when you're hanging it off the ballon is an exercise left to the reader. However, what you really need to think about here is that the antenna and whatever you do to feet it at the correct point is going to add even more weight. So your ballon gets bigger again. Where is this big, tough, durable, storable ballon coming from? How are you going to store and transport enough He to inflate it when the ballon goes up (ha!).

It works, it's been done in the past, but the logistics are not trivial.

Also doesn't help that no CB antenna is allowed to be more than 20' higher than the structure to which it's mounted (not relevant here) or 60' AGL, whichever is lower. 60' is NOT worth going through this effort!

The Jinxmedic wrote:
I'm not an expert, but I believe that CB antenna length is a function of its percentage of the frequency wavelength. (Radio experts, please correct as needed.)

ALL antennas are sized in relation to the frequency at which they're supposed to be operating. CBs use relatively long wavelengths so you end up with relatively large antennas.

Quote:
Also, my understanding is that a good sized groundplane is also beneficial to transmitting to maximum range. (this is why an antenna mounted square on the roof of your car works better than one mounted on the corner of a fender.)

Yes, RF groundplane is absolutely a critical factor in antenna performance. Yes, RF groundplanes need to be large, flat, and right at the base of the antenna. Hence roofs good, fenders bad. But here's where reality bites us in the ass: the ideal RF groundplane for CB is a circle a little over 9 feet in radius! I have not personally seen a car with a roof 18 feet wide by 18 feet long! This means that any piece of metal on a car is actually a bad RF groundplane so we need to make the best of a bad situation. That means putting the antenna in the middle of the largest piece of flat metal you've got.


gary in ohio wrote:
CB radio is not nor has it ever been a long range radio service. mobile to mobile 5 miles, 10-20 miles mobile/base at little more base to base. A bigger antenna isnt going to greatly improve the distances. Yea people can talk 100+ miles with an illegal amp, but not reliability when ever they want. Only when the bands up. If the band conditions are not favorable, no amount of power or antenna will help.

Answer this: does a megaphone help you, the user, hear better?

No, and neither do power amps. They help you shout more. However, they're still limited by RF-line-of-sight issues. The additional power really only helps "burn through" vegetation, buildings, etc. The key issue is the "band being open". What that means is that certain layers of the atmosphere are in a correct ionization state that the radio waves reflect off of them rather than traveling out into space. So the radio wave leaves your car at a bit of an up angle, travels WAY up into the sky, hits a useful layer of the ionosphere, and reflects back down to earth, landing on the receiver of another radio hundreds of miles beyond the RF-line-of-sight.

When the band conditions are right, power is nearly irrelevant to how far you can talk. There's an award in the ham community for "miles per Watt", meaning how far away you talked vs how much power you had to put into it. The problem with miles/Watt is that everyone was getting too little of numbers! So it became miles/milliwatt. Then thousand miles per milliwatt! People were using extremely weak transmitters, about equivalent to what you have in your garage door opener, and talking all the way around the world just by using really good antennas, really good technique, and great band conditions. Heck, guys do "EME" (earth-moon-earth, basically bouncing a signal off the moon and back to earth) on 5W (roughly CB-power) just by using crazy antennas.


gary in ohio wrote:
The ground plane for a fender mount or roof mount is exactly the same. The entire care is the ground plane.

This is absolutely untrue! If the entire car is perfectly electrically bonded (and it's not), you'd be minimally right in that the entire car would be radiating/receiving at least a little RF. However, the extreme, huge, internet-doesn't-have-a-smiley-serious-enough emphasis is on *little*! The RF groundplane is basically a mirror for the antenna to provide the "other half" of the dipole. Think about looking at yourself in the mirror; the best image of yourself is going to be with a large, perfectly flat mirror dead in front of you. Now, think about coating your entire car in chrome to make it a mirror. Some places on the car are going to be better image-formers than others. The places that are large and close to flat are going to be the best image-formers and the places that are small and highly curved are going to be the worst image formers. The fender is tiny and highly curved. The tiny means that it's terribly inefficient (can't see a full image in it) and the curved means the image is all distorted (like a funhouse mirror). Crap image former and crap place to put an antenna. On most vehicles, the roof represents the largest, flattest mirror and therefore the best place to put an antenna.

Quote:
Mount on the roof gives you the most omni direction patter where fender mount tends to put the signal more forward and out from the fender.

Close but not quite. The shape of the RF groundplane and the location of the antenna within it absolutely determines the radiation patter, you got that bit right. However, the preferential direction of radiation will always be in the direction of the most metal (to make a pretty severe approximation). So an antenna on the left fender will be almost deaf to the left side of the car but will preferentially hear and talk towards the right side of the car. If the antenna is near the front bumper, the antenna will also be nearly deaf in front of the vehicle and will preferentially radiate and receive to the rear. If the antenna is on the fender back near the windshield, the reverse is true and you can hear/talk forwards but not backwards.

For in-convoy distances (a couple hundred yards at most), these effects can safely be ignored. However, when you start trying to talk a couple of miles, they become very significant.


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PostPosted: Wed Jan 04, 2012 2:55 pm 
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gary in ohio wrote:
The best CB antenna is a 17ft whip mounted in the center of the root. This is hardly practical so EVERY CB antenna is a compromise. being the short distances most people talk. Any antenna over 4ft or so will do fine. The higher the better, but you take what you can get.


If you're going to go to ridiculous lengths (couldn't resist the pun) with your antenna, why stop at only a half wave? :mrgreen:

In truth, the "best" antenna is the one that works for your situation and allows you to make the contact.

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PostPosted: Wed Jan 04, 2012 4:43 pm 
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KJ4VOV wrote:
If you're going to go to ridiculous lengths (couldn't resist the pun) with your antenna, why stop at only a half wave? :mrgreen:



Because everyone knows a half-wave is the ideal isotropic antenna :D

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