At 04:03 PM 2008-04-12, Paul Young G0HWC wrote:
>I have been reading up on the TAK-Tenna and would like to build one
>for 20m and 40m. Anyone for the details for this ?
>
>Also, anyone tried building a 80m TAK ?
There has been some discussion about the Tak-tennas on the TowerTalk
list. Start at
http://lists.contesting.com/archives//html/Towertalk/2008-04/msg00319.html
The comments from K4SAV are especially pertinent.
The conclusion is that the "antenna" serves to drive currents down
the shield of the feedline, which actually does the vast majority of
the radiating. Tapping the two "pancake" coils asymmetrically
adjusts the coupling to the coax shield and lets you get a good match.
On 40m, the radiation resistance of the antenna itself is only a few
ohms, most of which is copper loss, since the radiation resistance of
such a small dipole is less than an ohm. The bandwidth is also very
narrow, which is typical of small antennas, regardless of the loading
method. If a choke balun were used at the feedpoint of the Tak-Tenna
so the feedline isn't part of the radiating system, the SWR would be
very high, even at resonance.
On the good side, for a very small antenna, this is a relatively
efficient design, since capacitive/inductive hats of this type do
tend to raise the radiation resistance near the maximum possible for
a 30 inch radiator. But the reality is that the bandwidth will still
be very narrow even after matching (with a hairpin, etc.) and
decoupling the coax shield.
I have some EZNEC models for 40m, which include the coax shield, if
anyone is interested.
73, Terry N6RY
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