"harry" wrote in
ups.com:

I have recently purchased two different VSWR Bridges.

One was made by Johnson.

The second is a clone.

Both use a fifty ohm resistor in series with the signal path. This
strikes me as a lossy setup. Is there a theory of operation posted or
a text which can explain the operation of the bridge?

Harry,

I am not familiar with the specific devices you mention, and you have
provided very little info.

I have made and used a device for impedance measurement that basically
had a 50 ohm resistor between tx and antenna sockets, and three
voltmeters to measure the RF voltage across the antenna, the internal 50
ohm resistor, and the combination. To make a measurement, you apply a
small amount of power at the desired frequency and measure the three
voltages. From those, you can calculate the antenna impedance, though
there is ambiguity about the sign of the antenna reactance.

If you have such a thing, they are for measurment only, you do not leave
them inline because of the losses, and of course, they will only
withstand very low power.

Do you think you may have such a thing?

Owen