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Cannot Adjust an IF Transformer’s cores
#15

Back at home for the evening, I've started modeling the circuit in KiCAD. I've attached my final schematic that I will use to order parts for testing. I mentioned it earlier on, but inductors come with a nominal self-resonant frequency (SRF, as most data sheets call it). I thought it would be appropriate to select an inductor with an SRF near to the resonant frequency I am striving for, but I was wrong. At any frequency above the SRF, and inductor will no longer behave linearly. You want to select an inductor with an SRF above your intended operating frequency. I was unable to find a 33 µH inductor with an SRF above 9.1 MHz, so I stepped it down to a 22 µH inductor. I found one with a minimum SRF of 12 MHz, which will work for my application. Thus, I need a total capacitance of 3.729 µF. I will accomplish this by using a 3.3 µF fixed capacitor and a 0.33 µF fixed capacitor in parallel, combined in parallel with a series connected 0.12 µF fixed capacitor and a 100 pF trimmer capacitor. See attached schematic for the general setup.

I will order some parts, and test this out on proto-board. Recall that I will still need to determine the appropriate separation of the two inductors in order to obtain critical coupling. And we shall see if I have refined the range enough to achieve resonance without a fuss. I should be able to adjust from 3.630099 µF to 3.75 µF, which puts the target 3.729 µF roughly in the middle of that range.


Attached Files
.pdf Philco 32-4257.pdf Size: 17.05 KB  Downloads: 56


Messages In This Thread
RE: Cannot Adjust an IF Transformer’s cores - by jrblasde - 07-31-2024, 08:05 PM
462ron - by 462ron - 08-01-2024, 07:33 AM
462ron - by 462ron - 08-01-2024, 08:44 AM
462ron - by 462ron - 08-02-2024, 08:09 AM
462ron - by 462ron - 08-03-2024, 07:49 AM
462ron - by 462ron - 08-04-2024, 08:15 AM
462ron - by 462ron - 08-08-2024, 08:02 AM
462ron - by 462ron - 08-10-2024, 08:33 AM
462ron - by 462ron - 08-10-2024, 09:38 AM
462ron - by 462ron - 08-12-2024, 07:42 AM
462ron - by 462ron - 08-25-2024, 08:27 AM



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