TopBand: Pennant antenna

[Earl W Cunningham]

Peter, VK3APN wrote:

>My thanks to Earl K6SE for publicising the Pennant antenna, which is
>reminiscent of a short terminated vee or half-rhombic. It is actually a
>very logical progression, come to think of it! I was about to try an
EWE,
>but this antenna looks even better. Before proceeding however, there 
>are a couple of points I want to clarify.
>
>Firstly, wouldn't the omnidirectional response of the vertical section
tend
>to fill in the rear null, or is there a phasing effect at work here?
========
Yes, there is a phasing effect.  The rear null is quite deep, greater
than 40 dB on 160m.
_
>Secondly, the fact that antenna dimensions had to be adjusted to
eliminate
>reactance implies that the pennant is not a pure travelling wave
antenna.
========
I don't believe the Pennant, Ewe, or Flag are traveling wave antennas
like the Beverage.  I feel they operate similar to phased arrays.  In the
Pennant, the top and bottom sloping wires are the other vertical
"element".
=======
_
>Could the reactance have been due to the vertical section, which is 
>inductive?
=======
I'm not quite sure what you mean.  In the Pennant antenna, the feedpoint
is capacitively reactive until the termination resistance is inserted. 
The value of the termination can be adjusted to yield zero reactance at
the frequency of interest. The "trick" in designing the Pennant was to
find the correct antenna dimensions which would give a good radiation
pattern when at the same time that the termination was adjusted to give
zero reactance.  There might be other combinations of size and
termination values which would work -- I don't know -- but 14' x 29' near
the ground with 900 ohms does work nicely for both the Pennant and the
Flag.

XE1UFO has proposed building a rotatable Pennant to put on his 50' tower
above his HF beam.  With the bottom of the Pennant at 53', the
termination in my model had to be lowered about 200 ohms (to 680) for the
point-fed Pennant and about 100 ohms (to 820) for a point-terminated
Pennant.

_
>
>Did you consider turning the pennant into a diamond (i.e. like a
vertical
>rhombic), where the open ends are brought back together? This would
>eliminate the vertical section, and with it the above (admittedly
>hypothetical) problems.  It should also improve the efficiency.
=========
Yes, I've played with a number of configurations, including the vertical
diamond.  That configuration also works quite well, but the rectangular
Flag antenna looks just as good.  Actually, the Flag is probably the best
of all configurations from a standpoint of broadbandedness and gain.  The
Flag has about 6 dB more gain than the equal-sized Pennant.  The Flag's
best size also turned out to be 14' x 29', BTW.  I'll look at the diamond
again simply because it's a configuration that would require only one
support a bit taller than for the others.

Always remember that all of these configurations have their directivity
in the opposite direction than that of a terminated Beverage or a
terminated rhombic.

And, IMHO, it's directivity that gives any antenna a better receive S/N
ratio.

73, de Earl, K6SE


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