CraigM,

1. If you look at many Transmitter Loading Coils.
They are often Bare Wire with Insulated "Spacers" that
provide an Air Gap. One of the "Features" of this 'design'
is to Allow for HEAT (Power) Dispensation.


2. Many Up-In-The-Air Antennas use "Loading Coils" that
are simply made of the same Insulated Wire or Bare Wire
used in the Antenna. Frequently there is a 'small' Air
Gap (about one to two wire diameters) in these Loading
Coils. Sometimes when Insulated Wire is used these
Loading Coils are simply wound with NO Air Gap.
But remember, there is the Gap (Spacing) that is created
by the Covering Insulation on both sides of the inner wire.

Loading Coil Looks Like: iWiiWiiWiiWiiWiiWiiWiiWiiWiiWi
"W" = Wire (Inner)
"i" = Insultation (Outer)


3. For Shortwave "SWL" Antennas that are Receive ONLY.
It is Simplier and Easier to use Insulated Wire and wrap
the Loading Coils using the Side-By-Side wire wrapping
method.

NOTE: An 'alternative method' is to use a "De-Wired
Insulated Wire" as a Spacer to create a Uniform Gap
between the Loading Coil's wire coils.

HOW TO: Estimate the length of the Wire required for
the Loading Coil; and "Cut" a second piece of Insulated
Wire to 'act' as a Spacer. Remove the 'inner wire'
from the Insulation and use the Hollow Insulation (Tube)
as a Spacer.


4. Cheap-and-Dirty "Loading Coil Form" = Simple and
Easy to Make. Basically use common PVC Pipe:

* 3/4" ID = 1" OD = Circumference 3.14"
+ Plus Factor in One #14 Insulated Wire Diameter (0.10")
= Length of One-Turn-of-the-Coil would be 3.46"

* 1.25" ID = 1.5" OD = Circumference 4.71" (Per Turn)
+ Plus Factor in One #14 Insualated Wire Diameter (0.10")
= Length of One-Turn-of-the-Coil would be 5.02"

HOW TO: Estimate the Lenght of your Loading Coil Winding Area.
Add Two Inches (3/4" PVC Pipe) or Three Inches (1.25" PVC Pipe)
to this for both PVC "End Caps" that will be used in the Form.
* Cut the PVC Pipe to Length.
* Glue on the End-Caps.
* Drill a 1/4" Hole in the Ends of each of the End-Caps.
[The End-Cap-Hole]
* Drill a 1/4" Hole at the PVC Pipe right next to the Edge
of each of the End-Caps. (Directly opposite each other.)
[The Side-Hole]

Use Black 1/4" Drip Irrigation Tubing (DIT) as a Strain
Relief for the Antenna Wire / Loading Coil Wire.
* Cut the DIT in to 4" pieces:
* Use two pieces of DIT per Loading Coil.

HOW TO: Building the Antenna "Loading Coil".
* Feed the Antenna Wire through one piece of DIT.
* Feed the Antenna Wire & DIT through the End-Cap-Hole
and around to the Side-Hole.
(About 2" out the End and 1/4" out the Side.)
* Jam about 1" of the Hollow Insulation (Tube) that is
being used as a Spacer into the Side-Hole.
* Wrap the Loading Coil using the Antenna Wire and the
Spacer as a Wire Pair.
* Use Electrical Tape to 'temporarily' hold the Antenna
Wire and Spacer in place on the PVC Pipe.
* Feed the Antenna Wire through the other piece of DIT.
* Feed the Antenna Wire & DIT through the other Side-Hole
and around to the End-Cap-Hole.
(About 2" out the End and 1/4" out the Side.)
* Trim the Hollow Insulation (Tube) Spacer Free-End
down to 1" and JAM that End into the other Side-Hole.
* Use RTV Silicone to Seal the Side-Holes and End-Cap-Holes.
NOTE: The "Remaining" Antenna Wire is routed to the Antenna's
Far End (Terminating Insulator) -or- the next Loading Coil.


OBTW: A copy of this Message has been posted to the YAHOO eGroup
"SWL Antennas and AM & FM Antennas" - Read Message #421:
* HOW-TO-BUILD: SWL Antenna Loading Coils - One Method
http://groups.yahoo.com/group/SWL-AM...na/message/421


iane ~ RHF
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= = = "craigm"
= = = wrote in message ...
"Telamon"
wrote in message news:telamon_spamshield-
...


At RF frequencies the coils are shorted electrically
because there is a lot of capacitance between them.
It won't work much better than a piece of metal the
same size. Coils can be useful as part of an antenna
if the turns are farther apart but as an element to
pick up RF energy from the air medium it will work poorly.

--
Telamon
Ventura, California

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I have a little trouble with this statement.

If there is so much capacitance between turns that you
have an effective short, then things like IF transformers
and AM loopstick antennas can't possibly work. A loading
coil at the base of a whip antenna is no more useful than
a chunk of metal? It just doesn't make sense.

Coils are added to antennas to increase their effective
length. If they just acted like a solid piece of metal
they couldn't do that.

craigm

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