H. Adam Stevens wrote:
Try quoting me correctly next time.
The word in the ad is "Handel."

Oops sorry, I thought you made a typo.
--
73, Cecil http://www.w5dxp.com

James Barrett wrote:

Hi, I'm not really sure what all of that means. I'm learning about
antennas, and I've been doing a lot of reading on the web until I can
get a copy of the ARRL Antenna book. I'm learning the terminology and
the other day read a thread about loading coils. I had no idea what that
was, so I went in search of an explanation. So, when I saw the radio
shop selling antennas with funny looking coils I wondered if that's what
a loading coil looked like. But I had expected a loading coil to be at
the bottom of the antenna, these looked like they might be in the middle
of the antenna. Does that even work?
. . .

The ARRL Antenna Book is a very good choice.

The function of a loading coil, as you've probably learned, is to add
inductive reactance at the feedpoint to cancel the capacitive reactance
normally present when the antenna is short. This results in a purely
resistive feedpoint impedance, which is the definition of resonance.
There's nothing magic about resonance insofar as antenna radiation
characteristics are concerned, but it often makes the antenna easier to
match to the transmitter.

You can put the loading coil anywhere along the length of the antenna.
As you move it higher, two things happen. The first is that the current
it's carrying decreases. This decreases the coil loss, which is
proportional to I^2. The other thing is that it has less effect on the
feedpoint reactance, so you need more inductance in the coil. This
increases the coil loss, which is approximately proportional to the
length of wire making up the coil (all else being equal). The net result
is that the overall coil loss is usually minimum at somewhere around the
middle of the whip, which is why center loading is often used. Another
benefit of center loading is that it might move the coil away from
objects which it can couple to in a way as to increase its loss.

That being said, W8JI has pointed out that at least on the lower
frequency bands, ground loss is so much greater than coil loss, that
there's no point in going to much trouble to minimize coil loss unless
it's outrageously high to begin with. This would have to be determined
on a case-by-case basis.

Have fun!

Roy Lewallen, W7EL

"James barrett" wrote in message
oups.com...
Hi, I was looking up antennas on google, and found a radio shop's
antenna page. These antennas have some kind of coil welded onto them.
Are these what you would call loading coils? And by the picture I
can't tell if the coil is at the bottom, middle or top of the antenna.
Any guesses?

http://www.mpaudio1.com/cbmobileantennas.html

Probably the bottom. The antennas are all shorter than a quarter wave and a
bottom loading coil would be likely.

What's with those power ratings? Thousands of times over legal CB and
unbelievable, too!

"James Barrett" wrote in message
. ..
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John Smith wrote:
art wrote:

...
yep, and this is where you get the amps to melt them
down:http://www.davemade.com/mobile.htm

You may be looking at the spring between the antenna and the bumper
which allows a long whip style antenna
to bend with the wind while mobile
Art


Ohh that's a loading coil alright, seen plenty of 'em at
cb-swap/meets/shows in the midwest. The shows used to be a lot more
open, now you have to know someone or be invited.

He should be warned, those BIG mobile amps draw a lot of amps and you'll
be into adding extra batteries in the trunk and alternators under the
hood! (think ambulance/swat-team/military vehicle industrial
alternators.)

Also, those BIG base amps can cause you to drop a new box into yer
house/shack to supply the power--above 5KW just gets too crazy, IMHO ...
and don't even think about it unless you have a place out in the boonies.

Anything above the smallest base amp with the big tubes is kinda
crazy--IMHO.

You want to run more power than that, think about starting up a real
am/fm broadcast station!

Regards,
JS

Hi, I'm not really sure what all of that means. I'm learning about
antennas, and I've been doing a lot of reading on the web until I can
get a copy of the ARRL Antenna book. I'm learning the terminology and
the other day read a thread about loading coils. I had no idea what that
was, so I went in search of an explanation. So, when I saw the radio
shop selling antennas with funny looking coils I wondered if that's what
a loading coil looked like. But I had expected a loading coil to be at
the bottom of the antenna, these looked like they might be in the middle
of the antenna. Does that even work?

BTW, I enjoy reading old threads from Roy and Cecil. A ton of great
information there. I have learned alot, and have much more to learn. I
want to try to make a 2 meter yagi (3 elements) this weekend and
experiment a little. Maybe I can finally hit that repeater 30 miles
away. ;-)

Jim

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generally the higher up the antenna the loading coil is the more efficient
the antenna is... but there are tradeoffs in mechanical strength and wind
load.

On Thu, 08 Nov 2007 22:37:51 +0000, Dave wrote:

"James barrett" wrote in message
oups.com...
Hi, I was looking up antennas on google, and found a radio shop's
antenna page. These antennas have some kind of coil welded onto them.
Are these what you would call loading coils? And by the picture I can't
tell if the coil is at the bottom, middle or top of the antenna. Any
guesses?

http://www.mpaudio1.com/cbmobileantennas.html


Jim


yep, and this is where you get the amps to melt them down:
http://www.davemade.com/mobile.htm

We just gotta get one of those "Rod of God" antennas! What a
hoot.....


--
-73 de Mike N3LI -

Jim,
Yes, they are loading coils. Specifically 'where' they are in the
antenna is very variable, just depends on the particular user, what he
has available, etc, etc.
One thing you should be aware of is that translating between 'CB'
electronics and everyone else's electronics is not always easy! The
'CB' world has proven that all the 'acceptable' assumptions assumed by
the rest of the world are mistaken in at least some way. Obtaining an
acceptable translation is very "iffy". (Nicest way I can think of to
say it's mostly total B.S., sorry.)
Examples:
Wider coil windings (straps) radiate better because or larger surface
areas, than measly small wire.
Wide coil windings that are 'flat', horizontal, radiate in a
horizontal polarization.
Vertical strap coil windings radiate in a vertical polarization.
'Fat' antennas can radiate gazzilions of watts whereas 'smaller'
diameter antennas can't.
MY antenna is better than your antenna because I made that way.
.... I quit. Probably gonna make someone mad or something.
- 'Doc

I'm trying to understand why a CB antenna needs to be able to "handel"
50,000 Watts. :0

Pete
AC7ZL

Cecil Moore wrote:
James barrett wrote:
Hi, I was looking up antennas on google, and found a radio shop's
antenna page. These antennas have some kind of coil welded onto them.
Are these what you would call loading coils? And by the picture I
can't tell if the coil is at the bottom, middle or top of the antenna.
Any guesses?

http://www.mpaudio1.com/cbmobileantennas.html

Presumably, the plastic looking things in the center
are insulators which makes the coils = loading coils.
But with CB antennas, one needs to be careful about
presumptions as some are designed for looks only.

H. P. Friedrichs wrote:
I'm trying to understand why a CB antenna needs to be able to "handel"
50,000 Watts. :0

Pete
AC7ZL

Probably has to do with the "Maserati Syndrome", you know, crazy people
with more money than sense and like high powered "things."

???

Regards,
JS

I'm trying to understand why a CB antenna needs to be able to "handel"
50,000 Watts. :0

------------

Easy!
Just in case it should ever have to. Right?
- 'Doc

H.P. Friedrichs wrote:
"I`m trying to understand why a CB antenna should "handel" 50,000
Watts."

Here we go again. Years ago we had a 50 KW CB thread that endured and
endured.

Best regards, Richard Harrison, KB5WZI