pdf 6436KB Sep 25 2010 04

Figure 1 — W2VJN in-band notching
fi lter schematic diagram.
Simple point-to-point wiring is adequate.
Four units were built to meet the requirements,
two for 80 meters and two for 75
meters.
Figures 1 and 3 detail construction
and performance details, and
Table 2 provides a list of components.
These units needed to be rugged enough
to withstand the long journey via air, sea
and ground to the operating positions on
Ducie Island. Small aluminum boxes were
used. The boards were mounted on four
threaded standoffs. Type F connectors
were used according to the 75 Ω system
requirements.
A three-element fi lter is simple enough
so that formal methods are not required,
and alignment can be done by alternately
adjusting each tuned circuit. Watching the
loss at the desired pass frequency and the
null depth on a network analyzer while
adjusting allows a good compromise to be
found. Figure3 shows the sweep response
of one of the units.
As Built on Ducie Island
As mentioned earlier, we did not build
out the entire system at the island. With
just a single receiver in the Elecraft K3 radios,
we required only half of the switching
matrix. We built the second parallel leg for
the 45°/225° Beverage. While this antenna
performed superbly, we did not feel very
strongly that we needed the second leg
on the other Beverages. We also worried
that adding the second leg — for example
to the 15°/195° Beverage — might introduce
a gap in coverage between the two
Beverage arrays, especially on 80/75 with
its narrower beamwidths. That gap would
run right through the middle of both the
US and Europe.
Results
Overall this system performed superbly.
There’s no question that it improved signalto-noise
ratio. The Beverage systems
delivered superior s/n ratios compared
to the transmitting antennas for these
bands. Dietmar, DL3DXX, summed up the
situation one evening around midnight,
after he had fi nished a lengthy 160 meter
operating session with Europe on a band
fi lled with static: “No Beverages? Then no
14 November/December 2008 NCJ
Figure 2 — Notching fi lter assembled unit.
Figure 3 — Typical notching fi lter measured response.
QSOs,” he said.
An operator could tell when sunrise occurred
in the Caribbean by comparing the
45° and 15° Beverages. The static level on
the 45° Beverage dropped signifi cantly as
sunrise moved across the Caribbean and
D-layer absorption attenuated QRN from
the thunderstorms in that region. The 15°
Beverage still heard plenty of static from
sources within its main beam.
This was the fi rst DXpedition where we
felt we could hear anyone calling us on
Top Band. In fact, at times we could hear
stations calling us much better than they
could hear us.
In terms of reducing QRM and dividing
pileups, the Beverages’ patterns appeared
to behave exactly as expected. The ARRL
International DX Contest (CW) occurred
early in the DXpedition, and station location
is part of the contest exchange. If a W6
called but was weaker on the 15° Beverage
(which covered California) and louder on
the 45° Beverage, we could be certain he
would be in the Eastern US, not on the
West Coast. The transition area where
stations exhibited equal strength on these
two particular Beverages was distinct and
narrow — from Texas through Arkansas
to Indiana and Michigan. These distinct
patterns meant that the operator could
focus on East Coast US stations during