On 1/22/2015 9:23 PM, Jim Brown wrote:
On Thu,1/22/2015 10:28 AM, Mike Reublin NF4L wrote:
I hope I get this correct:
The word "Balun" is a contraction, or a concatenation of two
abbreviations (Bal) for Balanced and (un) for unbalanced. In other
words, Balanced to unbalanced. Jim's RF "chokes are not "baluns", They
are simply a broadband REF choke of a relatively high impedance of
roughly 5000 ohms if wound correctly according to his tutorial. He has
graphs that display the impedance and bandwidth for the number of turns
and number of cores, for a given core material and mix. They, usuing
the concatenations are UnUns or simply unbalanced to highly unbalanced
antennas such as, center fed, half wave, fan dipole. Very few, if any
dipoles are truly balanced. Most are far enough off balance to benefit
from the application of the broad band RF choke.The sloping dipoles
usually need then. Some actually need two..
The matching networks for the Cushcraft R series and Hy-gain AV 640 and
AV 680 use both RF chokes and Baluns although some may argue with the
use of balun on the RF transformer because these antennas are not
balanced They are feeding effectively a combination 1/4 wave, loaded
radiator, using decoupling stubs, capacity hats. and/or traps or a
combination of traps and decoupling stubs against a small counterpoise.
The small, fixed dimension counterpoise is not a balanced radiator
although the RF transformer and the RF choke make it appear as
one...more or less. Several have rewound the RF transformer for a
better match on the Cushcraft R series of antennas. The RF transformer
matches the impedance while the RF choke takes care of the unbalanced
condition. .
The RF choke is used to keep RF off the coax, in the antenna and out of
the shack. It does a great job of doing that with the center fed, half
wave fan dipole on 75. Although it take two of them in my installation.
They also reduce noise pickup on the coax. Then, the choke feeds a
Balun/RF transformer which is also an RF transformer feeding the antenna
in a rather balanced manner. I say balanced manner because these
antennas are not balanced.
73
Roger (K9RI)
I think the confusion exists because we insist on calling too many
things "ground". To me, ground is earth. In electrical circuits
(AC,DC,RF) there is return. I doubt the world is gonna adapt my view.
That is EXACTLY the problem, Mike. We try to solve hum, buzz, and RFI
problems and make antennas work better by driving ground rods, when
those ground rods don't help any of those things (except, of course,
for RX antennas).
What DOES solve hum, buzz, and RFI problems is proper termination of
cable shields, and BONDING all equipment together. What DOES make
antennas work better is providing a return for antenna current that
goes good places and not bad ones. That means providing a good
counterpoise or radials for end-fed wires (including verticals) and
using common mode chokes to keep antenna current off of feedlines.
BTW -- we exactly the same problem with the word "balun," which is
used to describe nearly a dozen very different things, leading to more
confusion and fuzzy thinking.
73, Jim K9YC
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--
73
Roger (K8RI)
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