Gunn-diode, baluns and X-band lab system

Hi, could somebody help me with these questions of mine:
1.Should a gunn-diode be forward or back biased to start to oscillate.

2. If I feed a dipole antenna with an unbalanced 75 Ohm coax, what happens ? Does the current distribution change ?If so why ? Why should I use a balun ?

3.I have acess to a X-band experimental waveguide lab set-up, there you can modulate the 10GHz carrier(gunn-diode) with a 1kHz square-wave. Why did the designers of the labsystem choose to allow the experimenter to modulate the carrier with 1kHz ? Is it for a more accurate meausrment of some parameter ?

4.Does somebody have a nice timediagram over the Gilbert mixer, (when diodes are on/off) as a function of the input signals ?

Regards,
StoppTidigare

A message to Odysseus: Couldn't you make your tutorials with a tool that is free availible , pleeeaaase ?(Like APLAC )

1. Gunn diode should be "properly" biased.
3. 1kHz mod is for detection purposes. With a simple diode detector you can observe the level of the signal.