ETS-Lindgren 3142D BiConiLog Antenna (Archived) - Manual (Page 10)

10 | Introduction
For any dipole-type antenna to transmit or receive energy most efficiently, the
length must be nearly a half-wavelength, which is about 4.6 meters long at
30 MHz, and 2.8 meters long at 50 MHz. Unfortunately, this is too unwieldy for
many anechoic chambers and test sites. The optional end plates make it appear
like an antenna twice as long as the 1.4 meter length. The result is approximately
a 10 dB improvement in low frequency transmit gain and receive antenna factor
compared to a same length regular bow tie.
With the end plates attached to the Model 3142D bow tie elements, the
equivalent dipole electrical length is increased, which decreases resonant
frequency and increases efficiency in the 20 MHz to 60 MHz range. Similarly, the
regular bow tie has a lower resonant frequency than an equal length single wire
dipole. The optional end plate has its first resonance at a frequency where its
length is about 0.22
λ
, a regular bow tie at a length of 0.3
λ
, and a tuned dipole
at about a length of 0.48
λ
. Thus, at 50 MHz the 1.4 meters-long end plate option
behaves as if a 2.8 meter tuned dipole. Cross-polar radiation is minimized
because current flow on one of the T end frames is almost completely cancelled
by the opposite-phased current on the other T end.
Tripod Options
ETS-Lindgren offers the following nonmetallic, non-reflective tripods for use at
both indoor and outdoor EMC test sites.
For easy horizontal and vertical polarization, the ETS-Lindgren
Model 7-TR tripod is recommended.
Archived 6/19/13