On Tue, 22 Apr 2008 21:04:37 -0700, John Larkin
wrote:

According to the Henney's Radio Engineering Handbook 4th ed (1950),
1N25 and 1N26 silcon point contact 'crystals' for use in UHF and SHF
converters (1 to 25 GHz) are discussed in commercial publications by
Cornelius in 1945; 1N34 and 1N38 germanium 'crystals' for use at VHF
(~200mHz) appear in publications the following year.

Waritime radar operated in the 195MHz-10,000MHz range.

1N21B 'crystal' mixers were used by GE in commercial 2GHz relay
service before 1948 and similar parts were used by Bell in multiplex
telephone and television relay systems at 4GHz around the same time.

RL