A few thoughts on heat tests and heaters

[Dave Halliday]

>>I saw a schematic on a radar transmitter for a air traffic control
>>tower.. it had a seperate schematic for nitrogen lines.. nitrogen is the
>>only way to cool without condensation supposedly..
>      
>     So was that an immersion system then? A pure liquid nitrogen bath would
>     certainly be anhydrous... Or was the nitrogen used in another manner?



With high-power radar, it is better to use physical waveguides than 
coaxial cable.  Waveguides are sealed metal channels whose physical 
dimentions are the same as one wavelength of the RF being carried - 
makes for a very low loss situation.

Only problem is that condensation kills the efficiency.  The 
waveguides are filled with pressurised Nitrogen ( a PSI or two above 
ambient ) and baked - silica gel removes the moisture and a pony 
bottle of N2 gas keeps any pinhole leaks from causing problems - 
positive pressure...




Obligatory audio information:

During WW2, the frequencies of RADAR were much lower and the
wavelength for the waves were about the same as the wavelengths
of sound waves in air.  There was a line of loudspeakers ( Karlsen? )
developed after WW2 that essentially took broadband RF antenna
designs and tweaked the impedences a bit to match a physical speaker
instead of an RF waveguide.

Very very high effeciency.  Frequency response was not linear but 
nothing else was at that time either so it didn't matter.





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