文档介绍：Practical
15 HF Antennas
This chapter addresses the practical
construction of HF antennas and ATUs.
Because the scale and range of HF
antennas is so extensive the chapter is
confined to the description and con-
struction of the monly used
antennas
END-FED WIRE ANTENNAS
The Simple End-Fed
Antenna
The simplest of all HF antennas is just
a length of wire, one end of which is
connected directly to a transmitter or
antenna tuning unit (ATU). An example
of such an antenna is shown in Fig
.
Connecting an antenna directly to the
transmitter is often discouraged
because of the close proximity of the
radiating element to house wiring and
domestic equipment. This undesirable
feature is aggravated by the fact that
wild excursions of feed impedance can
occur when changing operation from
band to band. Also, good matching can
sometimes be difficult to achieve. Fig : The end-fed antenna, the simplest of all multi-band antennas
Choice of wire length may alleviate this
problem and is discussed in detail later,
see Matching and Tuning. An inverted L
antenna, as shown in Fig is often
referred to as a Marconi antenna.
However, the end-fed antenna is sim-
ple, cheap, and easy to erect; suits
many house and garden layouts and is
equally amenable to base or portable
operation.
Remote End-Fed Antenna
Having the antenna feedpoint remote
from the shack (Fig ) can circum-
vent the disadvantages of bringing the
end of an antenna into the shack.
Locating the long-wire antenna feed-
point away from the house minimises
EMC problems on transmit on receive
(electrical noise). Furthermore, it
reduces the unpredictable effect on the
antenna caused by possible conduit,
wiring and water pipe resonances.
The disadvantage of this arrange-
ment is that the ATU is some distance
from the transceiver, and this can be
rather inconvenient when es to
making adjustments. Methods of over-
coming this problem is discussed in Fig : A