system of changing directivity of the antennas and remote erasure
adjustments as outlined is somewhat inconvenient because of required
travel, terrain condition, time consumption and the fact that
the antenna when made directive in one direction is not available
for service in the opposite direction.
these undesirable features, a modified arrangement of the terminal
coupling units and rejection system may be employed which permits
the use of a two-conductor wave antenna for unidirectional reception
both forward and rear simultaneously on the same or different
frequencies with the band for which the antennas are designed,
and with all variable factors under control at the receiver.
The circuit is shown in Figure 6.
signals are delivered from the near antenna terminal coupling
transformers to a terminal rack through two 400-ohm transmission
lines connected to a Graybar #223-A, three-point, switchboard
jack. The receiver input lead connects to the terminating
jack through a short length of good quality lamp cord and a Graybar
3-A phone cord plug. A fixed one-watt resistance unit of
proper value is connected across points 1 and 2 of the Graybar
jack which automatically connects across the transmission lines
when the receiver plug is out.
In the event
the erection of more than one wave antenna may be contemplated,
the question of inter-coupling may arise.
Tests covering this feature at Grand Island using a standard signal generator
indicated that broadcast band wave antennas may be crossed within
a few feet of one another at angles of sixty degrees or more without
detrimental coupling effects or may be safely paralleled when
spaced four hundred feet or more; in either case without noticeable
or excess coupling.
When the antenna conductors run parallel over wire fences with non-conducting
supports, the fence wires, to avoid interaction, should be broken
with insulators at even lengths of about seventy-five feet.
Conductors such as fence wires and metal posts rubbing against one another
within a hundred feet or so of the antenna may be assumed to be
a source of noise generation in the antennas.