[Elecraft] Re: k3 SWR readings seem generous

[Don Wilhelm]

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
>