[TowerTalk] RF Ground is not a Myth

[Roger (K8RI) on TT]

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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