This is the next chapter in the antenna measuring saga. Today's adventure is
trying to measure SWR with an HP 8405A Vector Voltmeter.

The measuring setup is a standard signal generator feeding a tee. One branch
feeds the A input of the 8405A and the other a 20 db directional configured in
reverse, that is feeding the out port. The assumption is the reflected signal
will be read correctly on the in port. The in port is then terminated or
connected to an antenna.

An open termination reads 180 degrees and a 50 Ohm termination reads 0 degrees
and 55 db down from the input. (I assume 20 of that is the coupler so I am
subtracting 20 from that reading - is that a correct assumption.)

Using the method to read the SWR on an antenna produces values very close to
those from several SWR meters used as controls. When the output is terminated in
25 Ohms (2 x 50 Ohm terminators on a tee) the reflected signal reads about 24.5
db. (The B channel won't calibrate to within 1/2 a db so readings are estimates)
Subtracting the 20 db bias yields 4.5 db. Within the error of the instrument
this is pretty close to an SWR of 2:1.

Is there an error in this logic? If the instrument is working well enough to
perform this calculation then it should support more complicated measurements.

Thanks - Dan