[Elecraft] K2 - 2nd Xtal Filter

[Geoffrey Mackenzie-Kennedy]

Hello Stewart,

Tail end IF Filter:  Given that the prime purpose of the 2nd IF Crystal
filter is to reduce wideband noise created by the MC1350 IF amplifier, which
comes out as audio "hiss", yes a better filter would do a better job
provided that it is wider than the SSB filter. BUT I suspect that the MC1350
would not be happy driving such a filter with its varying input impedance.
More distortion / intermod would result than when driving the two crystal
filter. The other possibility is that the drive to the AGC system could
"bounce" due to these impedance variations, and depending on time constants
etc oscillation at some frequency high or low could result. An Image Reject
Demodulator can eliminate the need for any "tail end" filter, but no room,

AGC Take-off point. Here I am guessing. It could be 1) To reduce the BFO
signal leaking through the demodulator that might drive the AGC. The filter
chops this down. 2) A simple matter of drive level  3) To reduce AGC Attack
delay.

73.
Geoff,
GM4ESD

----- Original Message -----
From: "Stewart Baker" <stewart at baker.nildram.co.uk>
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Saturday, March 05, 2005 11:27 AM
Subject: [Elecraft] K2 - 2nd Xtal Filter


Anyone any experience of, or thoughts about adding another 3 crystals to the
K2
2nd crystal filter ?

73
Stewart G3RXQ