n6ry at arrl.net
Sun Jul 12 20:28:26 PDT 2009
This is easy to model in EZNEC. I used the original 29x14 foot
dimensions from K6SE's article in the July 2000 QST with two point-fed
pennants with their points separated by 1 foot.
The pattern and gain with or without the second pennant are essentially
identical. Whether the input to the second pennant is open, shorted, or
resistively terminated, the signal in the load resistor of the idle
pennant is only 8.5 milliwatts with 1500 watts fed to the active pennant
(don't try this with a real antenna!). Even though the two antennas
fire towards each other, it is typical for non-resonant antennas of
small dimensions (in wavelengths) to have low coupling. This property
also makes it very easy to design phased arrays.
If you use point-terminated pennants and put the feedpoints on the
vertical wires separated by 1 foot, surprisingly, there is still only
about 2 watts in the load resistor (1500 watt drive to the other
pennant), and the patterns are only slightly different. With this
layout, it would be better to use point-fed pennants so they would fire
away from each other, but then the feedpoints would be far apart. This
arrangement has a slightly larger (~2 dB) low angle back lobe than a
single point-fed pennant, but essentially the same gain.
Of course, you can also use a single pennant or flag with two
transformers and two feedlines and terminate the unused port to do quick
switching. In fact, you can use both ports at the same time if the
input Z to the receivers is near 50 ohms (which may not actually be the
case) and the transformers are designed to step up to the desired load Z.
I can supply patterns or EZNEC models if anyone is interested.
73, Terry N6RY
On 2009-07-11 4:11 AM, aa4nn wrote:
> Has anyone modeled two pennants with their
> feedpoints back-to-back like on the same support
> mast for easy switching short path to long path?
> In other words, does the switched out pennant
> influence the receive pattern of the active pennant?
> de Joe, aa4nn
> Lake Wylie, SC
> Antennaware mailing list
> Antennaware at contesting.com
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