Topband: T Vertical feed

[Joe Subich, W4TV]

On 1/26/2012 11:55 PM, DAVID CUTHBERT wrote:
> No I mean no balun is needed. The coaxial cable external shield
> current will be roughly that of one radial. With so many radials the
> shield current will be low.

This is a terrible error in logic.  Current on the radials will divide
based on the impedance of each radial.  If the feedline happens to be
a "pathological" length its (outer) shield can carry *all* of the
antenna return current.

Worse yet, even if the feedline shield carries only a fraction of the
antenna return current, if the length is such that it places the rig
at a high impedance point, the RF voltage can get quite high causing
"bites" or burns to the operator or significant damage to sensitive
solid state devices (not counting RF feedback or operational issues).

73,

    ... Joe, W4TV


On 1/26/2012 11:55 PM, DAVID CUTHBERT wrote:
> No I mean no balun is needed. The coaxial cable external shield current
> will be roughly that of one radial. With so many radials the shield current
> will be low.
>
> Dave WX7G
> On Jan 26, 2012 9:49 PM, "Jim Brown"<jim at audiosystemsgroup.com>  wrote:
>
>> On 1/26/2012 4:08 PM, DAVID CUTHBERT wrote:
>>> No balun is needed.
>>
>> What you mean, I think, is that no IMPEDANCE TRANSFORMATION is needed.
>> Yet another example of why I object to the word "balun."  And I agree
>> that no impedance transformation is needed at the antenna as long as
>> some sort of matching is used in the shack.
>>
>> But a common mode choke IS a good thing, because it keeps RF off the coax.
>>
>> 73, Jim K9YC
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