1 Introduction
Thank you for buying a Cross Country Wireless HF Vee Active Antenna.
It was originally designed as part of a contract to replace existing passive
antennas for a professional HF signals monitoring organisation.
It is a wideband active antenna with excellent performance designed and built
with high quality materials to last for years.
2 Theory of operation
The Active Vee Antenna uses a short balanced upright vee dipole to sense the
electric component of the electromagnetic field. The pattern and polarity of the
antenna is nearly omnidirectional with sensitivity to vertically polarised signals as
well as horizontally polarised signals. Muonted close to ground at around 5m agl
the antenna is ideal or NVIS use on 3 to 0 MHz.
The short elements used in the Active Vee Antenna have a very high impedance
with a capacitance of 2 pF over a wide bandwidth.
In the head unit a balanced amplifier using high linearity low noise transistors is
used with a matching balun to match the high impedance of the antenna
elements . Diode limiters and high voltage ceramic capacitors provide protection
from local high RF fields and static electricity from falling rain and snow.
The balanced amplifier feeds an isolation transformer matched to the 00 ohm
balanced load of the ethernet cable connecting the head and base units.
At the base unit another isolation transformer is used to match the 00 ohm
balanced load of the ethernet cable.
Any RF signal or noise induced in the ethernet cable as a common mode signal
is rejected by both transformers.
A diode limiter provide protection from excess RF voltages to receivers
connected to the BNC connector.
DC power is fed from the base unit to the head unit via a current sensing circuit
indicating the remote connection of the head unit with the illumination of a red
LED. Balanced filter networks at each end isolate common mode RF signals and
noise from the head unit amplifier.
