Wimpie wrote:
Hello Cecil,

On 27 abr, 20:13, Cecil Moore wrote:
On Apr 27, 10:30 am, Wimpie wrote:

Depending on the frequency resolution of your VSA, the frequency of
the injected signal can be well within 1 kHz of the carrier, so LC
filters in the PA will not distort the measurement. In case of a 100W
PA and injection of about 100 mW, the difference in wanted signal and
signal to be rejected is 30 dB (not that large).
Would any competent optical physicist suggest that it is valid to
study the conditions associated with interfering coherent light waves
inside an interferometer by introducing an incoherent light source
into the system? Why would any competent RF engineer suggest that the
system source conditions associated with interfering coherent RF waves
can be studied by introducing an incoherent test signal?

As this slightly off-carrier frequency signal behaves like a load with
very low VSWR with a cable in between that extends with constant
speed. In other words, the amplifier sees a constant VSWR, but with
changing phase. Small frequency difference results in slow phase
change of VSWR.


to the device under test, this isn't much different than a electrically
controlled line stretcher (a classic automated load pull setup... see
the stuff from Maury Microwave, for instance)

It's a very clever technique. A variant is used in antenna ranges where
you have a probe with a mismatch in it.