Posted by
Don Wilhelm on
Dec 06, 2018; 2:54pm
URL: http://elecraft.85.s1.nabble.com/Flumoxed-tp7646765p7646863.html
That statement is true - however ---
The problem is not radiation from the conductor, but how to get the RF
current into the conductor and not in other unintended places.
For those who want to build their own antennas, I suggest starting with
a resonant dipole fed in the center. That provides a good match for 50
ohm coax, and a good current mode choke (balun) at the feedpoint keeps
RF from flowing back onto the outer shield of the coax which can create
a lot of RF in the Shack.
Off Center Fed, and End Fed antennas can be made to work with more care.
The feedpoint impedance does not match coax, and special care must be
used to keep the RF on the radiator rather than coming back into the shack.
I realize that OCF and End-Fed non-resonant antennas are popular because
they can be used on multiple bands, but there are problems feeding them
while keeping the RF on the radiator and not in unintended places such
as the shack.
For those who want multiband operation, I still suggest a center fed
radiator fed with open wire or ladder-line to a good current mode choke
balun at transition point to coax is a better choice than OCF or end-fed
antennas - keep the coax short and use a tuner that can match the
resulting impedance.
Make the length of the dipole approximately the length of a half-wave at
the lowest operating frequency desired. It will be more "tame" for RF
in the Shack than many OCF or End-fed antennas.
73,
Don W3FPR
On 12/6/2018 8:56 AM, ANDY DURBIN wrote:
> "RF current into a conductor will radiate, even if it's at eye level."
>
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