[Prev][Next][Index][Thread]

Re: Rotary Gaps

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.  Most of
the "big boys" used a single turn primary, incorporating the
"condenser" in one side and the gap electrodes in the other.
	I have a full collection of QST magazines here, dating
back to the original in 
December, 1915, and it is amazing to see some of the truly
professional looking setups whose photos were published, along
with some rats nest nightmares.  Some of those guys really
knew what they were doing!!!!
	Wonder what radar set used the rotary you mentioned,
with electrodes like a tongue depressor?
Ed Phillips