[amsat-bb] 10GHz experiment question

["William Leijenaar" <pe1rah@xxxxxxxxxxx>]

Hi AMSATs,

Yesterday after work I have done some new tests again with my X-band test 
setup :o)
I managed to get a pulsed 10GHz output and I wanted to do some radar tests 
by measuring the pulse phase difference between the tx and rx :)

I take the 10GHz gunn-diode transmitter and next to it I placed the diode 
detector (both waveguides) It was working great, I could detect reflections 
very well, but I find out something I am not sure about it. What I find out 
is that the output amplitude changes with the distance to the object (object 
that reflects the tx energy to the rx input).
It changes very rapidly...

I suspect it is a mixture of several reflections what gives nulls and 
maximums, but it also occurs at very small distances when the object is just 
a few mm away from the in/output. At a few mm there are not many reflections 
from other objects what makes me believe less in this theory.

The gunn-diode is followed by a directional coupler, so it is not the load 
that changes the gunn-diode behaviour or matching. Behind the directional 
coupler I placed a pin diode switch to pulse the output, maybe this is the 
one that is effected ?
The detector I use is a simple 1N23 in a waveguide, where I read the DC 
output on an oscilloscope.

Maybe its somewhere it the books, but I couldn't find it out yet...

73 de PE1RAH,
William
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