In article .com,
"RHF" wrote:
Telamon wrote:
In article .com,
"RHF" wrote:
Telamon wrote:
In article . com,
"RHF" wrote:
JHR,
The Grove "Flex-Tenna" HVU Shortwave Listening (SWL) Antenna
http://groups.yahoo.com/group/Shortw...a/message/9886
Yes having the two Wires Parallel and within an 1/8" of each
other should effectively have the signals cancel each other out.
- B U T - The Wires are not the same length and therefore
a-differential is created between the two signal levels in the
two Wires. Because In-Fact the Two Wires are of Different
Wave Lengths.
One must 'assume' that Grove did some Design Planning or
practical Trial-and-Error Testing to get the Length of the Two
Wires so that they would give good results across the HF,
VHF and UHF Bands.
* 24 Feet is a little short for a 1/4 WL for the 31 Metre Band.
* 19 Feet is a little short for a 1/4 WL for the 25 Metre Band.
For Shortwave {High Frequency Only} one might try building
the same type of "Flex-Tenna Antenna made from Speaker
Wire with Two Wires that are a little Longer and have a Greater
'difference' in the Wave Lengths :
Shortwave Upper-Middle Bands :
* 38 Feet (a little short) for a 1/4 WL for the 49 Metre Band.
* 24 Feet (a little short) for a 1/4 WL for the 31 Metre Band.
= Delta of 14 Feet
Shortwave Lower - Middle Bands :
* 47 Feet (a little short) for a 1/4 WL for the 60 Metre Band.
* 31 Feet (a little short) for a 1/4 WL for the 41 Metre Band.
= Delta of 16 Feet
NOTE - The Flex-Tenna Antenna design lends itself to Speaker Wire;
Twin-Lead and Ladder-Line "Parallel" Wire type wire-structures.
Coax Cable for this Design of Antenna would not work IMHO.
The Outer-Shield of the Coax Cable would effectively Shield the
Section of the Inner Conductor of the Coax Cable and thus only
result in the Shield and Delta-Tip functioning as the 'differential'
Wire Antenna Elements.
FWIW - Most of the Coax Cable 'Liner' Antenna Designs are
basically End-Fed Dipoles beginning with a 1/4 WL of Coax
Shield with an ending with 1/4 WL of Exposed Inner Conductor.
The Grove "Flex-Tenna" HVU Shortwave Listening (SWL) Antenna
http://groups.yahoo.com/group/Shortw...a/message/9818
You could make a similar antenna out of coax but it would be more bulky
than the Grove version.
You can make loop antennas with coax that are balanced antennas. The
loops made of coax can be made sensitive to the E and M fields or just
the M field.
You could use the speaker wire to make a loop antenna that was sensitive
to the E and M fields.
Telamon,
Maybe someone could do some modeling of these two
types of Wire Antenna
First a piece of Speaker Wire with one Wire 24 Feet long
and the other Wire 19 Feet long using an "F" Connector
at the common Feed-Point-End.
Second a piece of Coax Cable with the Outer Shield
Terminated at 19 Feet and the Inner Conductor with
the Insulation still around it continuing for another
Five Feet for a Total Length of 24 Feet - again using
an "F" Connector at the common Feed-Point-End.
Some How I Do Not Think That They Are The Same Antenna.
but i could be wrong -and- you could be right - iane ~ RHF
Yeah, that would not.
I was think more along the lines of:
Starting from the radio the coax center conductor goes to the antenna
jack tip and the shield is not connected to anything. This coax is 19
feet long. At the coax far end the center conductor and shield are
connected together and a single insulated wire continues another five
feet starting at the center/shield junction.
Telamon - Your discription requires some thinking ~ RHF
19 Feet Coax & 5 Feet Wire
===================|
o------------------------------------|-----
===================|
Some how i think it comes out
19 Feet & 5 Feet
-------------------|-----
o
The shield is a 19 foot element and the 5 foot single insulated wire is
a continuation of it where the connection to this element is offset from
the end by 5 feet.
--
Telamon
Ventura, California