OK, slowly but surely, I got behind the mystery that is perceived in the numbers I occasionally publish.
The mystery goes as follows:
Use the cheapest available material (i.e. electronic components) in order to be active in the ranges in which radio amateurs are allowed to operate. That's it! No secret message in here!
We want to operate (transmit or receive) in the 40m band CW (Morse code or telegraphy) section, we can easily use a superhet (supersonic heterodyne) design mixing two different frequencies such as 8.867Mhz and 1.843MHz resulting in two mixing products, the sum which results in 10.71MHz and the difference resulting in 7.024MHz. Using a low pass filter, one will remove the sum of the two frequencies and end up with the difference, which is at a very convenient place on the telegraphy portion of the 40m amateur radio band.
The trick, or secret if you insist, is to use two standard crystals, which are cheap to obtain anywhere, and mix those up.... that's all.... In a superhet receiver design, one of those frequencies can be used as an intermediate frequency filter, using simple ladder filters, made from those cheaply available standard crystals.
Please, go through all the numbers I published so far and tell me if there is anything wrong with those... Some combinations are to be found on this blog, some here and even more here.
As I said, experts, please ignore this....