During some weather conditions such as snow or dust storms,
or summer electrical storms, voltages sufficiently high to break
down unprotected coupling coil insulation are developed in the
antenna system. To prevent transformer damage from all but
direct lightning strikes, L. S. Braasch #270 neon-argon tube arresters or their equivalent
with breakdown range of 200 to 300 volts may be connected to the
two antenna terminals and ground at both far and near ends of
the antenna; also to both terminals of the transmission line from
antenna to receivers when the length exceeds two hundred feet.
The ordinary 1-watt I.R.C. metallized resistance units as used
at Grand Island for terminal impedances will almost always be
found open circuited after each electrical storm occurring in
the vicinity of the antennas whether or not protected by arresters.
Where it is not practical to erect the antenna with
the near terminal direct to receiver location, it can be located
at any distance up to a half-mile or more from receiver location
and the signals brought to the receiver by transmission lines
without noticeable loss. For long stretches the four parallel
#14 B & S conductor type of transmission line is preferred.
For distances of 100 feet or less requiring no intermediate supports
the two conductors transposed line may be employed. Two
or more transmission lines may be mounted on the same poles or
other non-conducting supports when the separation equals or exceeds
ten times the spacing of the transmission line conductors.
A coupling transformer
with astatic shield is required at the receiver to keep the transmission
line balanced and prevent possible pickup of the transmission
line getting into the receiver.
When this resistance unit
does not itself absorb or reject undesired interfering signals
delivered to the receiver while the antenna is in service in the
opposite direction, a shilded L.C.R. circuit, Figure 7, also terminated with a short length of lamp cord and a Graybar 3-A
plug is inserted in the opposite reception jack of the antenna
and by manipulation of C and R the interfering signal can generally
be largely or completely erased without reduction in strength
of the desired signal, when the interfering signal is more than
90° from the direction of maximum reception of the antenna.
It is not as effective for signals predominately sky wave because
of their varying phase and intensity.
casual experiments and observations in service indicate that by
disconnecting and grounding one or the other of the conductors
of a two-conductor antenna at the station terminal, the forward
reception pattern can be changed sufficiently to permit partial
or complete erasure of interfering signals originating thirty
or more degrees from either side of the antenna, depending upon
which conductor is grounded and without noticeably affecting the
strength of the desired signal originating more nearly directly
forward or from an angle opposite the grounded conductor.