Monday, November 26, 2018

filter response - with 4 position selector and tuning capacitor.

There was a question asked and this is a start point towards the answer.The question is what is this filters response at the different ranges.

So we have 4 bands and 4 responses to look at. The cap is variable and should cover the ranges shown on the drawing. Starting in position 4 we have 2 coils and one cap in the circuit.

This is the circuit with the cap a max.
This is the frequency response with the cap at max.
Reducing the cap to 200pf gives this response.  The schematic note says it tunes 16 - 54 MHz. A 300nh coil needs 329pf to tune 16 MHz and 29 pf to tune 54 MHz. And so it goes....
To see the response for position 3 move the switches to 3 and add the coils. You feed L4 to ground and L1,L2 and L3 in series to the capacitor..............

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