Why the gain?

[The Jerk]

Why do the large open coil antennas, like the 55s/Fatboys and the Predator 10k, seem to have more gain than a true 1/4 wave 102-inch? I've seen time and time again where people state they replaced a 102 with a large coil antenna and gained both RX and TX...why would that be??

Or is it simply there are other underlying variables that could have made the difference and there isn't really that much difference when all variables are equal?

I'm considering trying a open coil antenna, I currently have a 102 set at an almost flat 1:1 SWR on all 40 right now. My main two concerns/holdups are the fact the open coils look like they would be bad news in winter (icing, snow buildup) and they look like they would be excellent at catching a passing branch...not to mention the alien-looking antenna.

 

[mackmobile43]

Why do the large open coil antennas, like the 55s/Fatboys and the Predator 10k, seem to have more gain than a true 1/4 wave 102-inch? I've seen time and time again where people state they replaced a 102 with a large coil antenna and gained both RX and TX...why would that be??

Or is it simply there are other underlying variables that could have made the difference and there isn't really that much difference when all variables are equal?

I'm considering trying a open coil antenna, I currently have a 102 set at an almost flat 1:1 SWR on all 40 right now. My main two concerns/holdups are the fact the open coils look like they would be bad news in winter (icing, snow buildup) and they look like they would be excellent at catching a passing branch...not to mention the alien-looking antenna.

Well if I understand by adding a coil higher on the antenna moves the rf voltages higher on the antenna and thus perhaps changing the take off angle of the antenna's radiation pattern as it sees it's counterpoise as it relates to tx but I could'nt say about the rx part of your question.

But I may be totally off on the first part also.

 

[Robb]

I am a big fan of the ol' 102" stainless steel whip. I'd keep it if I were you.
You could always get an antenna switch and hook up both antenna and see which one you like more. My bet is, that you will find that the steel whip will be better. Although the Monkey-made coil will be impressive and work well. Steel whips are both mechanically and electrically impressive in TX and RX. You should Google the 102" steel whip and see what others say - and why - you will find a lot of people that know just how good they are.

I used to have one with a crappy mobile CB and got fantastic reports with it. The Db gain is really xlnt! They even make decent base antennas if you construct a ground plane system from solid-core #8 ga copper wire - either 120 degrees or 90 degrees apart (go for the 90 degrees though). Flat match at 1:1.1. Doesn't get much better than that. As Mackmobile43 said the position of the loading coil is effective and allows for fine resonance.

The problem that you face is that a steel whip - when moving - doesn't stay perpendicular to the ground - that is their weakness. However when stationary - and with a large ground plane surface - you can get great DX/RX and use all kinds of power on them. Truckers like the Monkey-made base coils because they are consistent when rolling and also handle a lot of power. They also have an unlimited lifetime warranty - which is almost unheard of as far as mobile antennas go. That is their strength - IMHO...

 

[W5LZ]

First you have to understand where 'gain' comes from. The only way to get any gain at all is to make a portion of that radiated signal go in a direction you want instead of the direction it would normally go. Move it around, sort of re-shape the radiation pattern to a more usable 'shape'. I guess that's most noticeable with beams, or directional antennas. An added element (or two, or three) makes the radiation from the back side go to the front side. It's the same with omnidirectional antennas except instead of moving that signal from the back to the front side, the radiation pattern sort of get's 'squashed', or flattened a bit. That's typically done (or seen, rather) with changing the length of the radiator (in terms of wave length), such as 1/4 wave, 1/2 wave, 5/8 wave and so on. that pattern changes from a sort of 'ball' to a sort of 'pancake' shape (lots of exaggeration there, but still close to being what happens).
An antenna doesn't make any energy or signal, it only radiates what's sent to it in a particular pattern. If you can shape that radiation pattern to something that's usable to you, that's good. You still don't get something for nothing, or that shaping of the radiation pattern isn't without a cost. The typical cost is that some of the potential signal is going to go some place that isn't where you want it. Sort of a misplaced 'lobe'. That isn't gonna make a lot of sense unless you've seen some of the changes in radiation patterns. Some look really 'odd', lobes going here, there, and who knows where else. there's some 'waste', but if you can get some of that signal going like you want it, who cares, it'll work better than it not going that way.
Aftr you work your way through all that mess, stop and think about it for a minute. The typical mobile antenna is a vertical. The way to change a vertical antenna's radiation pattern is through adjusting it's height/length, not adding other elements to the antenna system (normally). So, in a very rough, generalization, making that mobile antenna shorter than about 1/4 wave length ain't gonna help that pattern shape much. May not hurt it, but it sure isn't gonna help it. About the only way to shorten an antenna is by adding a coil to it. That typically means that any antenna that has a coil in it isn't gonna produce the radiation pattern a 'full sized' one will. It's going to be a compromise. The good side of that compromise is that a shorter antenna can usually be made stronger mechanically so that it doesn't bend over like a typical 1/4 wave antenna does. So that it 'acts' like it has the same characteristics of that 1/4 wave at times. But, not all the time. If you can 'live' with that compromise, then by all means, use that stronger, shorter antenna. If not, then use that tree banging long thingy.
That ought'a keep you busy for a while, and I gotta go run them @#$ reindeer of the @#$ roof. Merry Christmas.
- 'Doc

 

[dudmuck]

The large open-coil antennas work better not because of the antenna itself, but instead where it is mounted on the vehicle: on the center of roof.

I would imagine that a 1/4 whip (with 4" spring) mounted on the center of roof might exceed height limit for many vehicles. So the whip is mounted in a substandard location causing degraded performance.

The vehicle chassis is the other half of the antenna.
If any this metal is higher than antenna mounting location, then performance is sacrificed.

 

[rfoverlord]

Wow if this isn't a loaded question! The ole gain game, stick with a 102" whip, like as previously stated. If you can't use one (mounting, body issues) that's when the elevated coil will come into play, as far as more "gain" well it's your money.

 

[BOOTY MONSTER]

hhhmmmmmmmmmmmmmmmmmm.... good egg nogg

i wonder how a fiberglass 102 with a solid/allthread spacer in place of a spring centered on a tool box on lil truck compared to a 17 or 22 inch 10k on the same roof would compare ? should be a lot straighter when driving.......?????

 

[W5LZ]

I would say it would act like an all steel whip of the same length, treated in the same way would. How would it compare to that '10k'? While I'm sure there would be some difference, I'm willing to bet that it wouldn't be much. If that fiberglass (or steel) whip would stay up straight, I'd have to lean in it's direction, so to speak...
- 'Doc

(all puns intended)

 

[The Jerk]

Thanks for all that...

So these guys claiming an improvement over the 102 are most likely seeing it because of their mount location and not the antenna itself?? That's sorta what I was thinking, but just wanted to see what others' thoughts were on the subject...

I only asked because some "indicate" they see big gains in both RX and TX (as in several s-units) moving from a 102 whip to an open coil...maybe its all in their head, so they feel better about their purchase?? I'm sure most of you have read similar threads...

I figured I'd ask before I spent some of that green on something I didn't need...

 

[Robb]

A lot of truckers run the MonkeyMade's in a co phase setup - which does a lot to establish a strong ground plane. And as others have said before, the disadvantage of the steel whip is wrapped up in the loss created by where it is mounted. Not to mention, the loss of being perpendicular when rolling. The advantage of the magnet mount base loads suddenly comes into focus, as they are a relatively low profile and get a good center spot for a better ground plane surface on/near the rear window (sedan).

I have a K-40 for the mobile because it is a trade-off of mounting options, and can run a modest amount of power thru it if I decide to do so. It doesn't mess with the sheet metal on the car - no drilling, mo mess, and no fuss. Of course, the Wilson 5000 is supposed to be the big boy on the block, as far as base load coils are concerned. You didn't exactly let us know what kind of vehicle you have, so that is an open question - too.
Here's an interesting link I found today.
Enjoy!
http://www.angelfire.com/psy/mrcoily/id10.htm
http://www.angelfire.com/psy/mrcoily/id20.htm

 

[The Jerk]

I've got the 102 mounted on a toolbox in the bed of the truck...probably less than 24" below the roof line of the cab.

 

[hookedon6]

Wow if this isn't a loaded question! The ole gain game... ... well it's your money...

exactly! it's not about "gain" at all, ...it's about reducing losses and increasing efficiency. from another thread: http://www.worldwidedx.com/cb-antennas/31548-stupid-antenna-mounting-next-level.html .....to increase performance and minimize the coil losses, the loading coil should be at or near the center of a whip antenna.
Xl must equal Xc for a whip antenna to achieve resonance. the loading coil is used to tune out capacitive reactance.

 

[W5LZ]

'Jerk,
There is no 'one' best antenna for -all- situations. There can be and are 'best' antennas for almost any ~particular~ situation. That situation thingy means where it is mounted, fixed, mobile, whatever. With a mobile, that 'situation' is changing all the time since it's moving, or things around it are moving, traffic. That means that what may work just dandy fine at some particular place/time/environment, may not work so good at another particular place/time/environment. Unless that antenna is changing along with it's surroundings. (If you should happen to run across one'a them kind'a antennas I wish you'd get two of them, the second one for me! I'm not going to hold my breath waiting for that to happen. Not that I think you wouldn't get me one too, I just don't think you'll ever find such a beasty.)
All things considered, the biggest difference between the typical 1/4 wave whip and a 'coiled' antenna is it's rigidity. The whip is just going to lean over at speed, the other won't, at least not to the same extent. So, I figure you've got about as good as it gets for the price you paid for it. If you want to spend 5 to 10 times as much for a very -slight- increase in performance, please, be my guest. (You can have the one reserved for me! Won't bother me a bit. )
When people start worrying about very slight possible improvements in what they have, I think they should take another look at the whole thing. As in, is it really worth that? The 'catch' is that while there may be some -slight- improvement, is it very practical, really, considering where it's going to be put, etc? If it's worth it to you, then do it. It's your wallet.
An antenna does not have to be resonant to perform well. It certainly doesn't hurt if it's resonant, but it isn't absolutely necessary. A 5/8 wave antenna is a very good example of that. The antenna isn't resonant all by it's self, the matching device that is used with it makes it appear to be resonant to the transmitter. Aside from one being resonant, the only difference between a 1/4 wave antenna and a 5/8 wave antenna is the shape of it's radiation pattern. That's it, just that. The 'shape' of the radiation pattern changes with length. Till you get to about 5/8 wave length, that change is typically to the better. After about 5/8 wave length, that 'shape' starts to get really sort of 'odd' looking and it typically isn't as 'good'. It's fairly easy to see if you happen to have an antenna modeling program (which also have limits and are NOT the 'cure all' of antennas). Get someone who isn't as lazy as I am to show you, it's very informative.
Shortening an antenna by adding inductive reactance, a coil, certainly works. The 'catch' is that there is always a loss of efficiency when that's done. One reason is that a coil is not very efficient to start with. The other reason is that the resulting radiation pattern will change to something 'less' than it was at 'full length'. That's one of those things that is just a fact of life, doesn't matter what anyone says, it always happens. Sometimes the benefits out weigh the loss, so it's worth doing. Other times, not. It's up to you to decide if it's worth it or not...
- 'Doc

 

[BOOTY MONSTER]

basically , sitting still a 108 it the better antenna . when driving a 10k will stay pretty much verticle and will out do a 108 laying back in the wind .
the 108 would probally be better for talking to someone on horozontal beams when driving though . hehehe

 

[Cat Driver]

Do like the HP here in Mo. do. They have the 102 mounted to the rear fender on the car an then a nylon? cord hooked from the top of the 102 running to a clip on the rain gutter of the car to keep it from bending over while going down the road.

Ron