RadioBanter - View Single Post

January 23rd 04, 03:36 PM

From: (Jerry=A0Oxendine)
"Duke Of Windsor" wrote in message
...
(Twistedhed) wrote in news:28004-40102BD9-249
@storefull-3256.bay.webtv.net:
From: ('Doc)
FWIW
=A0=A0A coil will always lower the power handling

ability of an antenna.

Balderdash. The coil will evenly distribute heat that would otherwise
fry a lesser, non-coiled antenna.
_

What he is trying to tell you is that a coil

DOES reduce the efficiency of a circuit as

opposed to a straight wire.

That is not what he said. There was NO comparison until you entered an
example.

That is something you can argue with all day

No need. What you said and what Paul said were two different things.

long and it will still be a fact.

What Paul said is not a fact. With your radio background and experience
with antennas, you should know his claim is no absolute.
The presence of a coil does not necessitate the reduction of efficiency.
In fact, the opposite is true in many instances an I'm really having a
difficult time believing you can't realize this.
There is a tradeoff in the design of many small antennas,,,,practicality
for sixe and all that jazz,,,,,in some of these cases, a coil actually
makes the said design more efficient.

Any coil creates resistance. If you wind a coil

of say #18 wire, it will also CREATE more

heat than that straight wire.

Which is where antennas are compromised by virtue of design for
practicality of size.
Nevertheless, the coils are efficient at dissipating heat, which can
often be a factor in making the antenna more efficient.

Where RF is

concerned, in a given circuit, it will be

resonant, but that heat wastes RF

energy . Along with it, it will also be more

"broad-banded" and tolerate a wider range of

frequencies.

My original statement said nothing of broadbandedness,,,I merely said
Paul was incorrect.

Now,

when you----and let's talk about antenna

coils-- use a larger coil, YES! It distributes

heat better,

Again,, "better" is often synonymous and construed as, "more efficient."

again a result of less resistance. It is also

called IMPEDANCE of which there are 3

"resistances": feedpoint impedance, COIL

resistance, and radiation resistance. Now. We

can't do much about radiation resistance, but

the other two can be used to advantage. With

the coil, again, it DOES dissapate heat AND

its bandwidth becomes NARROWER. That

means that

if you are sitting still and the antenna's

environment doesn't change (like with those

keydown events) the

antenna remains in resonance. If the vehicle is
moved, then it's effficiency *can* suffer

because its environment changes along with

it. That cell tower that wasn't there before now

can have a BIG effect on the antenna's overall
performance. It also may not be as big an

effect

at 27 MHZ as it would be at lower frequencies,
but it is an effect no less.

Which is why the antenna testing ranges are free of obstacles. Paul's
coil statement still is incorrect without qualification.

According to established antenna theory, a

102" whip would outperform that big coil.

Theory is only that,,,,,"theory",,otherwise it would be fact. In all
seriousness, that whip is gonna fry with mo' watts!

The

reason they don't is that *most* users put the

whip on the bumper and when they install a

Predator 10K, they put it on the tool

box (pickup) or the roof. Now the parameters

have changed and the user now believes that

the coil is "better". Sure, it's better, but the coil

antenna now has

gained a height advantage.And this has as

much to do with the antenna's FEEDPOINT

and proximity to the earth With the whip on the
roof or tool box, the coil should not outperform
the 102: whip, but whips are impractical and

they don't *usually* end up on top because of

their height.

A local muddin' club has several trucks with whips on the roof and even
a Jeep with a whip on the rollbar.

Antenna theory is the same for any radio

service whether it is CB or any other.

Jerry

Yep,,a theory is but only the best explanation we can offer for all that
we can't explain and the real world tinkerers know that theory does not
always hold in real world applications, especially in endeavors such as
radio and antenna design, otherwise, the products would never advance or
improve, as they would be at an impasse.