[HBR] My approach to the HBR... Suggestions?

[Hopperdhh at aol.com]

In a message dated 9/13/2008 1:38:05 P.M.  Eastern Daylight Time, 
radioconnection at gmail.com writes:
Thanks!  I'll  check the link.  How do I model the coupling between the coils 
in the  IF?

Pete,

You have to specify a mutual inductance.  See the  help file under 
transformers.  There will be a learning curve as you become  familiar with running the 
program, but it isn't that hard.  Also, it is  great for drawing schematics.

The mutual inductance (M) is approximately  L/Q for critical coupling 
assuming equal L's in primary and secondary.   Assume a little less than that for 
when the coils are pulled apart and a little  more when they are together.  (The 
85 Kc cans have an adjustment stick  coming out of the top.)  You can play 
with the M value just like changing a  capacitor value.  It's much easier than 
the real world!  As you  make M too big you should see the double hump response, 
just like in the  text books.

A good way to keep the Spice model honest is to compare its  output with 
actual bandwidth data from a simple test circuit using the actual IF  can.  First 
get one tuned circuit to agree with the model, then adjust M in  the model 
until the coupled circuits agree.

Maybe the model won't work  for you exactly, but I guarantee that you will 
learn something while trying to  make it work!

Dan K9WEK  




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