Practical_Antenna_Handbook_0071639586

360 p a r t V : h i g h - F r e q u e n c y A n t e n n a s f o r S p e c i a l i z e d U s e s
Incoming
signal
To receiver 14'
R T
Incoming
signal
To receiver
8'
14' R T
28'
Figure 14.21A Pennant antenna.
Figure 14.21B Flag antenna.
The pennant (Fig. 14.21A) was developed by Jose Mata, EA3VY, and Earl Cunningham,
then-K6SE (deceased), to overcome the EWE’s sensitivity to the characteristics of
the ground beneath it. The resulting pennant design exhibits stability of pattern and
performance over a wide variety of grounds and can be raised (on a mast) to a wide
range of heights. The favored design also tweaks dimensions and terminating resistor
value to arrive at a purely resistive feedpoint impedance for optimum matching with a
9:1 transformer.
Just as the pennant is a triangular receiving antenna, the flag (Fig. 14.21B) is a rectangular
one. Because the capture area of a flag is somewhat larger than that of a pennant,
the flag antenna provides somewhat greater output voltage to the feedline for a
given signal than does the pennant.
Unlike the Beverage, all these antennas receive away from the terminating resistor.
All must be mounted on, or supported by, nonmetallic members (such as PVC pipe)
and must not be located near any metallic structures—especially those having dimensions
in the vertical plane that are a sizeable fraction of a wavelength at LF through
lower HF frequencies—unless steps are taken to detune those structures at the frequencies
of interest while receiving.
Many amateurs and BCLs have employed multiple phased pennants and flags to
obtain even greater improvements in received signal-to-noise ratio. An Internet search
on these antenna types will return many detailed and useful references.
Longwire Antennas
No discussion of HF receiving antennas would be complete without mention of the
longwire antenna. This is often the first external antenna ever used by a broadcast band
DXer or SWL. Its primary attribute is simplicity. Its primary disadvantage is that it has
a pattern that is either unpredictable or shifts from broadside to axial with increasing
frequency. However, the beauty of this antenna is that if it is at least 100 ft long, it can
provide hours of enjoyable listening to anything from VLF airport beacons through the
AM broadcast band and on up into the amateur and international shortwave broadcast
bands. The author has even used a longwire with receivers (such as small portables)
that had no provision for connecting to an external antenna. Simply bring the end of the
longwire near the receiver—perhaps wrapping it around the receiver enclosure a few
turns.
Unfortunately, that same “one size fits all” versatility means the longwire rejects
nothing, and strong off-frequency signals can overload just about any receiver unless