[Heathkit] HW 100 CXR NULL

[Kenneth G. Gordon]

> On the LSB null capacitor,

Whoa! 

Where did you get the idea that the null capacitor is for LSB only? 

It is not! 

Nor is the null-adjust pot only for USB. 

You have to adjust BOTH of those while switching between LSB 
and USB, and compromise so that you have about equal carrier 
suppression in both modes.

I have found that changing the null-pot for a 10 turn 200 ohm pot 
from Mouser or Newark makes adjusting the null considerably 
easier.

I also use a scope, since that makes it far easier for me to see what 
is happening.

If the null-capacitor is fully-meshed or fully-open, then you have to 
adjust the value of one of the small SM caps in the bridge.

I've also found that you get 1) better carrier suppression, and 2) 
better balance LSB/USB if you change all four of the diodes in the 
bridge to hot-carrier types, also available from Mouser or Newark.

Ken Gordon W7EKB