[Elecraft] K2 SSB receive mods

[Lyle Johnson]

> ...I am also looking for more detailed theory on how
> the receiver's variable bandwidth crystal filter works.

Wes Hayward W7ZOI has published several articles on ladder crystal filters
and their design.  Go to the ARRL website and do a search.

Also, MFJ publishes "Ladder Crystal Filters" by N2DCH which is a good
reference for this class of filter.

Finally, at the US Patent Office up can retrieve patent 5,051,711 which
covers the variable bandwidth filter using varactor diodes for tuning.

73,

Lyle KK7P