[Microwave] Before the Friis equation

[Dr. Gerald N. Johnson]

Friis was probably involved at MIT or Harvard during WW2. There is some 
discussion of the radar equation (propagation loss plus reflection loss) 
in Volume 1, Radar System Engineering, pages 18 to 21. Then volume 13 is 
on Propagation of Short Radio Waves. By short they meant shorter than a 
meter or a quarter meter. I don't have time this morning to read in 
either much, but these were published '47 and '48 but represent the best 
work of the World War II years. The two volume set from Harvard from the 
same era is called. "Very High Frequency Techniques." And I'm sure has a 
chapter on propagation. These being both reports of fundamental 
theoretical and experimental research do include many references to 
older work. MIT Rad Lab volumes are available free on line, Very High 
Frequency Techniques may be harder to find.

73, Jerry, K0CQ

On 8/16/2014 4:22 AM, Dave Brown wrote:
>
> 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
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