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Re: Rotary Gaps

Quoting ed-at-alumni.caltech.edu (Edward V. Phillips):

> Re: Volume 5 of Radiation Lab Radar Series
> Richard:

> You may have overlooked one comment there (can't quote
> page and line as my copy is in my book case at work) which 
> mentioned that the guys at Rad Labs tried some of the earlier
> "radio transmitter" rotating gaps and found they didn't work
> any better than the ones they eventually ended up with, which
> mostly had pointed electrodes.  I have seen many radar 
> modulatro (modulator) spark gaps, and all had more or less 
> sharp points. The flat, wide electrodes came about because of 
> the desire to keep the circuit resistance very low.  An 
> "ultimate" ham transmitter at 200 meters (1500 kHz) used an 
> 0.01 mfd capacitor, with a reactance of about 11 ohms.  Any 
> circuit resistance at all knocked the primary circuit Q 
> (increased the decrement) to pieces.  

Yeah, I have noticed this. The points keep the dwell and quench
times low.

> Wonder what radar set used the rotary you mentioned,
> with electrodes like a tongue depressor?

The rotor electrodes were thin, say 3/16 inch, tungsten. Only the
stationary electrode was flat, and mounted so that it would
pivot. By pivoting the stationary electrode the dwell could be
adjusted.

Richard Quick





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