Phil,
There is a huge electrical difference between switching an additional
inductor in series with the load (or a capacitor in parallel) than what
is commonly seen as "hot-switching" which results in the amplifier
seeing an open circuit until the relay closes. A very high RF voltage
will exist if the PA is operated into an open circuit.
During the tuner's tune cycle, the load is never open circuit to the PA,
and the resulting RF voltage is kept under control.
73,
Don W3FPR
Phil & Debbie Salas wrote:
"Hot switching RF in an external ATU is not to be recommended for
any radio at any level."
BUT - you DO hot-switch your K3's RF output when using any relay-based
auto-tuner, including the internal K3 auto-tuner. So my reasoning is
that I'd rather hot-switch the 100-watt PA at 15 watts rather than the
10-watt PA at 5 watts. And then, my MFJ-998 (which I use with my
ALS-600) reads SWR more accurately at 15 watts than it does at 5
watts, so when I go to full power the tuned SWR is still minimum. As
Wayne stated earlier, SWR readings at low power may be less accurate
due to the detector diode voltage drop at low power.
Phil - AD5X
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