Peter, welcome to the forum
Have you seen http://ww2talk.com/index.php?threads...nit-msu.74246/ . It does not answer your question, but as the thread is similar to your query, there is someone on the WW2 Talk forum (Stefan) who might be able to help if you are unable to find an answer here.
There is also an RAF Signals Museum at http://www.rafsignalsmuseum.org.uk/S...Flyer2015.pdf; perhaps its Curator could help.
Brian
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