[CQ-Contest] [TowerTalk] EH Antenna - or when is a shield not a shield?

[Kelly Taylor]

It is perhaps related to too much time in close proximity of said
feedline...

73, kelly
ve4xt
----- Original Message ----- 
From: "Dudley Chapman" <chief at thechief.com>
To: <towertalk at contesting.com>
Sent: Friday, November 11, 2005 12:02 PM
Subject: Re: [TowerTalk] EH Antenna - or when is a shield not a shield?


> Tom wrote...
>
> >Actually Ted Hart, who claims to be the inventor of the EH
> >antenna, gave a stern warning to never use common mode
> >chokes on the feedline of EH antennas because it stops the
> >system from working. What Hart actually said was:
> >
> >"If you use RF beads, since the coax shield is not a
> >magnetic shield, the beads affect both the inner and outer
> >conductors. Therefore, most of the transmitter power will be
> >converted to heat. Not good."
> >
> >He also said:
> >
> >"RF on the Coax
> >Due to the large radiation at the EH Antenna, there will be
> >some RF coupling to the coax. Whether this is a problem is
> >dependent on the radio you use. Some are subject to RF
> >coupling into the audio system, which causes severe
> >distortion while transmitting. On some field day setups with
> >100 watt transmitters we have had so much RF on the radio
> >you can get an RF burn. Below we have suggested ways to
> >eliminate the RF coupling problem."
> >
> >73 Tom
> >
> >
>
> Tom,
>    Yes, these fringe ideas stick around because the theory always looks
> reasonable, except for an innocuous looking but terribly fatal flaw.  In
> this case:
>
> "...the beads affect both the inner and outer conductors."
>
> Not only is this totally bogus but the justification for this bogosity is
> found by reading between the lines of the following:
>
> "Therefore, most of the transmitter power will be converted to heat. Not
> good."
>
> To which I would add: (Yes, not good because all that heat represents what
> would have been fierce feedline radiation.  Without that the antenna by
> itself doesn't work as he rightfully asserts in the first paragraph.)
>
> What motivates an otherwise intelligent person to say something like this?
> Perhaps the answer can be found in his support of the Kor Radiation
theory.
>
> Dudley - WA1X
>
>
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