[Microwave] Before the Friis equation

[Dave Brown]

Any historians out there?
I'm currently looking into some experimental work that was carried out in 
the 1930s involving long VHF radio paths. Those involved were amateurs but 
also recent university graduates.  It seems that back then, little if 
anything, was known about calculating free space path loss. This is hardly 
surprising as most research at that time was based round propagation from 
VLF up to HF. Any work at higher frequencies was purely experimental with 
few, if any, practical applications in mind for the frequencies beyond 30 
MHz.

The Friis equation, published just after WW2  in Proc IRE for May 1946 (pdf 
here)
http://dsc.ufcg.edu.br/~maspohn/adhoc-grad/papers/Friis%20transmission%20equation/01697062.pdf
appears to have been the first time that straight forward calculation of 
free space path loss was brought to the attention of the scientific and 
engineering community.

The early (1930s) texts I've looked at so far fail to mention anything 
beyond use of what appear to be mainly empirical relationships for 
estimating field strength at a distance, which was a prime consideration for 
LF/MF broadcasting.  HF communications was then in its infancy and the 
effect of the ionosphere was barely understood and yet to have  a well 
developed theoretical basis established.

 I'd like to establish whether or not any published work exists that 
predates the Friis article  in dealing with the calculation of free space 
path loss or the related concept of the ratio of received and transmitted 
powers, including the effects of antennas, over the theoretical free space 
path.

Friis, in his 1946 article, notes that  his equation has been in use for 
some years -" Almost seven years of intensive use" - but makes no mention of 
the concept having been published earlier. This suggests strongly that WW2 
(and probably radar related research) provided the impetus to provide a 
sound theoretical basis for this type of calculation, but if anyone can 
provide any references to earlier relevant published work for me I would be 
most grateful.

73
 Dave
ZL3FJ