Message-ID: <4.2.0.58.20000308102754.00988750@mail.pncl.co.uk>
Date: Wed, 08 Mar 2000 10:35:12 +0000
To: rsgb_lf_group@blacksheep.org
From: "Walter Blanchard" <blanch@pncl.co.uk>
Subject: LF: VLF
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Flg might be of interest to the SM boys thinking of going on 8 kHz. I found 
it in the memoirs of Dr Jack Pierce (MIT, USA) who had a hand in the design 
of Omega and Loran-C :

"On the occasion I found most interesting, the boys in Hawaii had pieced 
together all the loading coils they could find and managed to get the small 
antenna at Haiku tuned to 6250 hertz. At this frequency the power radiated 
could not have been more than a very few milliwatts. I observed the signal 
at Cambridge (Massachusetts, USA) with our photographic technique, using 
triggering pulses at a submultiple frequency, so that a cycle or two stood 
still on an oscilloscope screen and the photographic record (which plotted 
the oscilloscope picture against time of day) appeared as black and white 
stripes. During the night the signal was marvelously clear but at sunrise 
it declined so rapidly that at first I thought that the transmitter had 
been turned off. This was because that frequency of the signal came close 
to or below the cutoff frequency in the waveguide-like space between the 
earth and the lowest ionized layer. The height of the layer dropped 
suddenly when the first rays of sunlight reached it in the morning, and the 
attenuation of the signal increased rapidly. This and one or two other 
experiments between six and ten kilohertz convinced us that reliable 
longdistance operation was not to be expected at all hours at a frequency 
much below ten kilohertz."
	
Date?  January 1946.
	
The "small antenna at Haiku"  was a 300 ft vertical! These experiments led 
to the development of Omega, 10.2, 11.666, and 13.3 kHz.
	
Walter G3JKV