Tuning is possible only in the
a) Preliminary information.
Tuning the amplifier involves a procedure of matching the impedance of the antenna and transmission
line to the amplifier tube’s characteristic load resistance. This will ensure maximum plate efficiency and
RF gain at nominal output power, with minimal distortion and spurious output. Note that
readings depend on the antenna and transmission line impedances only, and not on amplifier
POWER readings depend on the antenna and transmission line impedances only, and not on amplifier POWER
tuning. If the load impedance is not a nominally resistive 50-Ohms, the
REFLECTED POWER reading will REFLECTED POWER
always show a reading, no matter what the tuning settings. Proper tuning is always necessary, however,
and will allow you to operate at a high power level, without distortion or any danger to the amplifier.
presented to the load (the antenna and transmission line)
OUTPUT POWER presented to the load (the antenna and transmission line) OUTPUT POWER
is equal to the difference between the
power readings. For instance,
with a 2.5:1 VSWR, readings of 800 W and 150 W
FORWARD POWER and FORWARD POWER
is 650 W. At very high VSWR levels, such as when no antenna
OUTPUT POWER is 650 W. At very high VSWR levels, such as when no antenna OUTPUT POWER
is connected or a badly mismatched antenna is used, the
be almost equal, while the real
(the difference between them) will be nearly zero.
OUTPUT POWER (the difference between them) will be nearly zero. OUTPUT POWER
The amplifier can operate safely as long as the
is LESS THAN 250 W. Matching
REFLECTED POWER is LESS THAN 250 W. Matching REFLECTED POWER
is assured for loads presenting a VSWR of up to 3:1. Nevertheless, for some loads and bands, matching is
possible at even higher VSWR levels, but the drive power must be reduced to prevent the
from exceeding 250W. Failure to comply with these guidelines will cause the protection circuits
POWER from exceeding 250W. Failure to comply with these guidelines will cause the protection circuits POWER
to trip. For example, if the antenna VSWR were 5:1, the maximum attainable forward power would
be 540 W, 240 W of reflected power and real output to the antenna and transmission line of only 300
W. In the event your antenna cannot be adjusted to produce a lower VSWR, an external antenna tuner
At elevated VSWR levels, high voltages and high currents are distributed along the
coaxial cable to the antenna, risking internal arcing and heat generation, and likely
damage to the cable and any antenna switches that may be used. It is recommended
that VSWR levels of more than 3:1 not be permitted with coaxial cable above 14
It is advisable to adjust amplifier tuning when antennas have been changed, snow has fallen, new objects
are in the near field of the antenna, etc. Such changes may affect antenna impedance.
If you use more than one antenna on a band, the proper antenna
prior to performing the tuning procedure outlined below.
To avoid damage not covered under warranty, do not switch the
while transmitting. As discussed above, hot switching will damage the amplifier’s
Also, never apply drive longer than one minute continuously without pausing for at
least one minute to allow the tube to cool.
To Next Page
Loading...
