Echoes from 1940

A few weeks ago, my wife brought me a library book to read entitled Winning the Radar War by Jack Nissen(thall) and A.W. Cockerill, published by Robert Hale, London in 1987.

This book, still widely available from the likes of Abe Books for about £5, is a fascinating read of the human experience of being a developer of radar during WW2.  There is not much technical stuff at all.

A typical Chain Home Low radar station of WW2.  Image courtesy Imperial War Museum.

 

There are always several books in the queue here, and this one has taken up residence on the bathroom reading table.  So I am reading it slowly, but carefully.

A fascinating account I've just come across reads as follows (p.76 in the 1989 edition):

'However, the really interesting experience that came out of my return visit [to Rosehearty Chain Home Low radar station, Scotland, around July-August 1940] was a discovery that altered forever the erroneous belief that radio waves travelled in straight lines [the author presumably speaks of VHF; the bending of radio waves over the horizon at HF had been known for decades]...

...The straight-line theory...was shattered one evening on radar watch.

I was intrigued by strong, even massive, signals coming to our receiver when the aerial was pointed in a north-east direction.  I remember thinking it odd that I hadn't noticed them before.  When the aerial was rotated, the signals vanished, so I had the binder [antenna rotating operator] crank the aerial back to the bearing of the blips and began checking to make sure that they weren't ghost signals. 

I studied them thoughtfully, consulted a map of the Scandinavian coastline, and finally came to the only conclusion that made sense to me.

The strong response was nothing less than a long-distance echo off Hardanger Mountains in Norway, over 300 miles away.  This meant the the supposedly impossible was happening: our 1.5 metre [~200MHz] transmissions could be, and in fact were being, bent around the curvature of the earth, giving us a reflection off the Norwegian mountains.'

Well, my thoughts are that whilst this could have been a terrestrial reflection, I wonder whether, given the NE direction and summer timing, it might instead have been returns from a Es or PMSE layer?  

I will have to see if a report the author filed about this event with a Dr. Ed Bowen - a Welsh physicist who made major contributions to radar development, is still kept in an archive somewhere.