PAGE 23
where F = Forward power (watts), R = Reflected power (watts)
SWR is measured using a device called an “SWR bridge”, inserted in the transmission line
between the transmitter and the antenna. This circuit measures forward and reflected power from
which SWR may be calculated (some meters calculate SWR for you). More advanced units can
measure forward and reflected power simultaneously, and show these values and SWR at the
same time.
An antenna tuner is a device
used to cancel out the effects of
antenna reactance. Tuners add
capacitance
to
cancel
out
inductive
reactance
in
the
antenna, and vice versa. Simple
tuners use variable capacitors
and inductors; the operator
adjusts them by hand while
observing reflected power on the
SWR meter until a minimum
SWR is reached. The LDG
Electronics
AT-1000ProII
automates this process.
No tuner will fix a bad
antenna. If the antenna is far
from
resonance,
the
inefficiencies inherent in such
operation are inescapable; it’s
simple physics. Much of the
transmitted
power
may
be
dissipated in the tuner as heat,
never reaching the antenna at all.
A tuner simply “fools” the
transmitter into behaving as
though
the
antenna
were
resonant, avoiding any damage
that might otherwise be caused
by high reflected power. For best performance, the antenna used should always be as close to
resonance as is practical.
SWR
1
R
F
1
R
F
Summary of Contents for AT-1000PROII
Page 8: ...PAGE 8...
