Re: Thoughts on Low Power and fewer turns on LP filter toroids

Arv Evans <arvid.evans@...>

In addition to Allison's comments, the filters are designed 
to work with 50 ohms input impedance and 50 ohms output 
impedance.  If either of those impedances are not 50 ohms 
the filter cutoff frequency will be impacted.


On Tue, Sep 8, 2020 at 11:29 AM ajparent1/KB1GMX <kb1gmx@...> wrote:

THe AL used for winding of toroids has a variation of 10-15% so depending on
how tightly wound  plus individual batches you get variation.

The Iron powder material is really like many high volume materials to get it
as close as they tend to be takes a significant bit of effort.  I strongly point
to the spec.

Add to that the caps used are 10% maybe 5% so when you plug in the variation 
it does get to be significant.  That said I'se used those very same table and
many over a 25 filters then tested them ( 5 bands * 5 per) and then tested
them and they were remarkably consistent.  Parts used were not the same
batches but were drawn from my own stocks some quite old.

Also did you adjust L4?

All 4 of those inductors interact and due to reflected impedances and determine
power and harmonic content.

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