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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
How do you intend to measure "what would happen"?
I can make a pretty good guess. The inductor will have a self-resonant frequency. Below that frequency it looks like an inductor. Above it, it looks like a capacitor.
Since the size of the inductor is significant compared to a wavelength, it'll also act as an antenna. You'll see a resistive part to its impedance, corresponding to the radiation resistance.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
If you are happy to do your microwave experiments over short distances - say a few hundred metres in a line of sight - then you can build everything yourself using very simple circuits made from inexpensive parts.
For example, at 2.3GHz, you could build a transmitter using just one active device - a suitable transistor or thermionic triode - and a super-regenerative receiver also using just one transistor or thermionic triode (followed by a single simple stage of audio amplification). In the early years of amateur radio on the microwave bands, this very type of equipment was used to communicate over tens of kilometres. The quality of the antenna, its feedline and matching, are central to successful microwave communication using this flea powered equipment, but is all very do-able at modest cost so long as everything is done with care.
The design and construction of amplification circuits at 2.3GHz - whether receiver signal amplification, or transmitter power amplification - is a specialised business intolerant of even small errors, and needing some fairly expensive test kit to set up properly, so I really wouldn't recommend it as a starter project.
You can make an RF field strength meter to detect your microwaves up to about 2.5GHz using very few and cheap parts - namely a suitable small signal diode, followed by a basic op-amp, and a meter that can measure microamps. You will need this to satisfy yourself that your one transistor microwave oscillator is in fact oscillating and radiating a signal, as Steve has hinted.
Determing the frequency of oscillation around 13cm is another matter, but if you are really strapped for cash you can get a very approximate result using the ancient technique of Lecher wires described here:
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On Microwave Transmission
