[Elecraft] K2 - Low Pass Filter location

[Vic K2VCO]

Phil Kane wrote:

>   My concern is with non-linear components in the KAT100 RF path
>   that would generate harmonics and negate the advantage of the
>   filter. Sampling diodes, as in a SWR bridge, are always suspect.
>   If this is to be a problem, I would have to get a second filter,
>   one for each antenna, which is something that I really don't want
>   to do unless I have to.

This is an interesting question, because it brings back memories of the 
good old days when everyone needed an LP filter because of VHF TVI!

Keep in mind that the diodes in the KAT100 are before the tuning 
elements, so that insofar as the L network acts as a LP filter it will 
reduce the harmonics generated by the diodes. But this will probably 
depend on the band and the impedance the KAT100 is working into.

Also keep in mind that the LP filter is designed to work into a 50 ohm 
resistive load and will be either lossy or ineffective if the impedance 
seen on the antenna side of the KAT100 varies much from this.

So I would put the LP filter before the KAT100 to deal with any 
harmonics generated in the K2, and hope that the tuner will eat anything 
the diodes make.

Do you really have harmonic VHF TVI with the K2?

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco