Anytime! It appears that the shorter lifetime diodes are used for the higher
frequencies (VHF / UHF). When I built my first receiver and was looking for
the right type of diode for the preselector, the engineer I was working with
said "you need to use some real slow dogs for these frequencies".
In one of Rohde's notes, I remember his stating that a diode with a 1.5uSec
minority carrier lifetime is usable down to around 200kHz. I have had good
experience with 1N5767s down to 10kHz, but I am sure that there is a rolloff
in sensitivity.

Pete

wrote in message
oups.com...
When I read lifetime, in my mind I was thinking shorter was better. In
fact, there are gold doped transistors where the gold is used to lower
the lifetime. However, the paper explained the longer lifetime means
lower resistance Thanks for the reference.