Hello everybody. Very close to me is a powerful FM radio station, it sims that it affects on the sensitivity of HackRF One, so the idea came to make a notch filter FM band.
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Schematics of FM notch filter
This is a four-circuit filter. The coils are wound with enameled wire 1 mm diameter, the winding diameter is 5 mm. coils L1, L2 – 2 turns, L3 – 12 turns, L4 – 14 turns, tuning capacitors 5-30 pF, additional capacitors of 82 pF format 0805. L1, C1 – 98 MHz. L2, C2 – 98 MHz. L3, C3 – 108 MHz. L4 C4 – 88 MHz. Estimated level reduction of 30 dB.
View of the board in 3D
Made a case from doublesided FR4.
We adjust the filter to the frequency of the nearby FM station 100.1 MHz with UR5FFR NWT
Testing the results with HackRF One