On Wed, 22 Mar 2006 21:01:37 GMT, Telamon
wrote:

In article ,
Bob Miller wrote:

On 21 Mar 2006 19:41:42 -0800, "RHF"
wrote:


SO HERE WE GO AGAIN - - - - - - - - - - - - - -
This is a Three Band : 49 & 31 & 22 Meter Bands
Shortwave Listener (SWL) "Receive Only" Tri-Band
Dipole {Wire} Antenna built on a On-the-Fence
Question What Do We Do To Make It 'perfrom' ? ? ?
? To Perform - Or Not To Perform - - - Is That a Question ?
A little better across the Shortwave Bands so we can
"HEAR" a little of everything from 1.8 MHz to 30 MHz.
Not a good answer but never the less a fair answer is
the 4:1 Balun to 'smooth-out' the impedance mismatches
from the Three (3) Dipole Antenna Elements and provide
a fair 'match' from the three of them across the Shortwave
Bands; know that they are One-Foot, Three-Feet and
Five-Feet above the ground when Idealy they would be :
49m = 38.5 Feet above AGL
31m = 24.5 Feet above AGL
22m = 17.1 Feet above AGL


I took into consideraton that there are three dipoles here, connected
to a single transmission line -- so hopefully each will be within
yelling distance, impedance wise, of 75 ohms, so there's no need for a
4-1 balun to a 50 ohm input.

Unless you want to transpose 75 ohms to about 20 ohms?

And if the antenna is less than a half-wavelength high at frequency,
on a fence so to speak, the impedance could be anywhere between 40 and
90 ohms, according to chap. 20 of the ARRL handbook. Still no need for
a 4-1 balun. Maybe a 1 to 1 choke balun, to sop up noise, but a 4-1?

What is it, this high religious SW fever for baluns in this group :-)

It's a way to current terminate a coax so it is not completely (100%)
dependent on the the antenna impedance for the source termination.

You want to have lengths of the dipoles to be high impedance respective
to each other so the characteristic impedance of the sum says around the
72 to 50 ohm range. You would then want to then use a 1:1 BALUN.


H-Y-P-O-C-R-I-T-E ALERT!!