Note also that the real OUTPUT POWER presented to the load (the antenna and transmission line) is equal
to the difference between the FORWARD and REFLECTED power readings. For instance, with a 2.4:1 SWR
load, readings of 1500 W and 250 W FORWARD POWER and REFLECTED POWER respectively, the real
OUTPUT POWER is 1250 W. At a very high SWR levels, such as when no antenna is connected or a badly
mismatched antenna is used, the FORWARD and REFLECTED readings will be almost equal, while the real
OUTPUT POWER (the difference between them) will be nearly zero.
The amplifier can operate safely if the following rule is obeyed:
"REFLECTED POWER < 300 W".
Also, impedance matching capability is assured for loads presenting a SWR of up to 3:1. Nevertheless, for
some loads and bands, matching is possible at even higher SWR levels. The maximum usable forward
power at a SWR of 3:1 is 1200 W with 300 W reflected. For higher than 300 W reflected power a
**REFLECTED POWER** SOFT-FAULT protection trip will occur.
For example, this can happen at full-scale 1500 W forward and 375 W reflected power, into an antenna
having a SWR of 3:1 or worse.
NOTICE
Using a feeder of coaxial cable at SWR > 3:1 on HF, and particularly on the 10- and
6 meters bands, is not recommended. At such high values of SWR, the high voltages,
high currents, and heat associated with line losses, risk to permanently damage your
coaxial cable or antenna switch.
It is highly advisable to re-adjust amplifier tuning when antennas have been changed.
Re-adjust amplifier tuning when you change the band or between CW and SSB segments within the same
band.
Update tuning periodically, even if you have not changed band or antenna, in particular when a significant
change in the environment occurs (snow, ice, newly appeared or removed massive objects, alien wires
nearby etc.) that would cause significant changes in the antenna impedance and an increased SWR.
If you use more than one antenna per band, it is necessary that you select the proper
antenna BEFORE the next step. Retune after selecting a different antenna for the same
band, since both impedances may differ substantially (unless their SWRs are excellent,
i.e., below 1.2:1 for both).
At SWR above 1.2, retuning is mandatory although the two SWRs might be nearly same,
for example 1.8 and 1.7 for the old and a new antenna. It might happen that one
antenna is 90 Ohms and the other - 30 Ohms, each requiring totally different tuning.
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