This seemingly unreasonable circuit connection is, apparently,
more effective during afternoon hours or for several hours before
local sunset. It is frequently not effective at all.
In some instances forward interfering strong signals
can be more completely balanced out by connecting a simple or
general purpose antenna to one of the terminals of the signal
rejector for clear reception of weak
signals on the same frequency originating in the rear.
In order to obtain a better balance at the far end, and
to partially or completely eliminate pickup by the vertical ground
lead at both far and near terminals, a Beverage reflection transformer,
6, is employed and a lead covered #12 B & S conductor
used as a shielded vertical ground connection. The conductor
with lead shield is made water tight at the bottom by soldering
conductor and shield together and connecting the whole to the
underground radials. The transformer housing is grounded
to the upper end of the lead shielding and the coil terminal to
the shielded conductor.
arrangement is an apparent improvement in directivity over the
exposed, directly grounded, vertical section of the antenna conductor.
TEST FOR TRANSMISSION
The transmission line may be checked for signal pickup or unbalance
by disconnecting the two antenna wires and connecting a resistance
across the transformer in place of the antenna and equal to the
surge impedance of the two antenna conductors. Very little
pickup of signal or noise should register in the receiver from
a well-balanced line.
TEST FOR TRANSFORMER BALANCE
coupling transformers may be tested for balance by the use of
a signal generator and receiver connected as shown in Figure 8. When properly balanced the receiver will
indicate nearly zero input or a very small transfer of energy
to the secondary of the transformer.
Impedances Ra and Rb in
Figure 6 should be equal to the surge impedance
of the transmission line as calculated from:
(s equals spacing from center of wires)
(d equals diameter of wire [d and s in
The transformer Ta couples the transmission line to the
two-conductor antenna and the two wires are now acting only as
transmission line to carry the reflected signal from A direction
to the receiver. The impedance of the two-conductor antenna
serving as a transmission line is calculated from the same formula. The
Grand Island transmission lines are approximately 400 ohms
and the antenna conductors 700 ohms.
The transformer Tb couples the transmission line to the antenna with
the two wires acting as if they were in parallel, because the
primary of Ta has