CV291 mixer diode ("crystal valve")
 |
This "valve" measures 20x7mm overall (~6mm across the main body) |
| Frequency of operation | 6000MHz |
| Min back to forward resistance ratio | 8:1 |
| Min forward resistance | 265 ohms |
| Max amount by which performance is below "standard best" | 3.0db |
| Max noise temperature ratio | 2.6 |
| Nominal IF impedance | 350 ohms |
The foil wrapping is designed to protect it from damage caused by RF fields.
Crystal valves were used in the mixers of radar receivers and were susceptible to burn-out caused by the high RF power of the transmitted pulse. It was for this reason that TR Cells were so vital in single-aerial operation, and also the reason for the development of thermionic diode mixers such as the CV58 and CV258.
(Note: Yes I know it is a semiconductor, but as these crystal valves were so vital to radar and many of my other unusual valves are for radar too, surely this deserves to be an 'honorary valve'!)
