Please Note:
A qualified structural engineer
should be consulted prior to mounting an
antenna on a tower or support structure.
Model LPD-12 225-400
General description.
The LPD-12 225-400 is a twelve element log periodic dipole antenna covering the frequency range
225 MHz-400 MHz. The antenna is designed for cantilever rear mounting to masts up to 3” O.D. to
provide vertical polarization.
Theory of operation.
The antenna is comprised of twelve dipole elements connected to a parallel pair of 1 1/4” alumi-
num crossarms that form the antenna transmission line. To accomplish end fire log periodic opera-
tion the elements are tapered from the front of the antenna to the back and successive dipole
halves are transposed along the antenna transmission line. An internal cable in one of the
crossarm sections functions as a balun to convert the balanced 50 ohm input at the front of the an-
tenna to 50 ohm unbalanced coaxial “N” type connector mounted at the rear of the antenna. This
internal “balun” effectively chokes off the surface currents normally associated with a balanced
feed and eliminates transmission line radiation.
The entire antenna is maintained at d.c. ground potential through the grounding of the crossarms
at the rear of the antenna. A ground wire attended to the crossarm mounting or the cable fitting
will drain off static build up and provide lightning protection.
ELECTRICAL CHARACTERISTICS (TYPICAL)
Instruction Sheet
30533-001 Rev. J
