Alec’s hobby of amateur (ham) radio hasn’t made much of an appearance here yet because he didn’t take it up until the 1960s, and then it spent some considerable time evolving. However – as there is a gap in the correspondence here – this seems a reasonable time to introduce the subject of QSL cards.
As Wikipedia tells us, a QSL card is sent from one amateur radio operator to another to confirm their communication. At one time these had a standard format, but over the years – as printing methods improved and materials became cheaper – they became more personalised. Alec must have sent out thousands – via the RSGB and/or his local club – over the years, and in due course received thousands in return. After his death a large box of QSL cards – roughly divided by geographical region – remained in the family’s possession until it was eventually passed on, together with his log books, to his only grandson Robin. (Robin is occasionally to be found on fora at sourceforge.net, and elsewhere online, using the screen name g3rrk.)
There were probably other variants, too, but these are the only known examples to have survived.