I found this online PDF handbook on PIN diodes.

Since many people in this goup might wish to make improvements
on thier receivers, and since most modern receivers use diodes as
either input filter switches, and/or IF filter switches, I thought
others
might find it as usefull as I have.

Changing the common Si switch didoes in the IF fitler section to PIN
diodes
is a simple and pretty inexpensive upgrade that can that help the
ulitmate
filter rejection. One of my R2000s' went from ~70dB to over 83dB. Very
worthwhile. I will be modifing the other 2 over the holiday.

For the front end octave filters, replacing the Si switch diodes with
PINS only
made significant improvements in the LW/MW and the crowded 6MHz and
9MHz bands. I won't be doing this mod on the other 2 receivers.

Terry