Started testing... or better preparing the test conditions.
It takes a while to adjust a good interference pattern. In the picture above there are too many rings, in the lower picture the pattern is much better.
I tested in the living room. The pattern was only useable after 11pm - with no movements in the room. Movements blur the pattern out, and it takes a few seconds to stabilize again.

The PA current must be set correctly to deliver RF, I noticed that the RX power is probably most suitable to detect resonance conditions.

Blue graph: RX power
Grey: Scanlines of the interferometer rings

Red: Frequency: 24000 MHz plus yellow scale

Green: Pixel sum between interference rings (results in a sine wave when multiple bright/dark regions are crossed) It helps to see small changes less than 1/2 wavelength.

I believe to see changes correlated with the frequency around 24500 MHz, as they seem to occur with bending of the interference pattern in several tests. But maybe I only see ghosts - that´s just an assumption.

I´ll take more tests today and will try to further stabilize the interference pattern before progressing with regular test runs.

I will also try several positions of the tuning screw - so it´s still a lot work to do.
I´ll be also very careful with shouting out positive results, unless I am convinced that there actually might be thrust.

It will be exciting, let´s see what happens.

About test data:

I will provide the software for free download, so you can easily browse the chart with realtime zoom function, including the 30fps scanlines of the interferometer rings.
There will be also an export function for the data into a CSV text format.