Sometimes the SWR meter changes the impedance seen by the transmitter.
To compare meters its best not to cascade them, but to measure the load
with one, then remove it and measure the same load at the same frequency
with the other.
Source impedance shouldn't change an SWR reading unless the SWR bridge
has poor directivity (rejection of power flow in the opposite direction
from the reading). I know Collins had stiff specifications about that
when Bruene developed their watt meter. They insisted on more than 30 dB
directivity. Shielding and lay out were critical to get that much
directivity. I have one of the rejects, and for my purposes it works
fine. When I have the tuner adjusted so the meter needle doesn't move on
reflected with near full scale on forward, the solid state transmitters
put out full power. I figure that's close enough.
73, Jerry, K0CQ
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