[R-390] IF Trimmer notes

[Roy Morgan]

At 09:10 PM 1/31/2006, Barry wrote:
>Cecil,
>
>Good analysis.  I'd assume that with any of the ceramic trimmer types, if
>you don't get two peaks (or nulls as the case may be), the cap isn't of
>sufficient value due to whatever due to the mechanical nature of their
>construction.


Barry and all,

It goes like this:

As the trimmer is rotated toward it's minimum value, the circuit begins to 
resonate but needs less capacitance than the minimum. Thus you get only one 
dip, but the dip is not at resonance.

OR:

As the trimmer is rotated toward it's MAXimum value, the circuit begins to 
resonate but needs more capacitance than the MAXimum. Thus you get only one 
dip, but the dip is not at resonance.

If the real resonance point is within the range of the trimmer, you'll get 
two dips, one on either side of maximum capacitance.

The same applies to air variables.   With slug tuned circuits, or with 
compression trimmers, you get more of a hint of what's going on because of 
the position of the shaft or screw.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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