I\`m trying to build a frequency modulated LC oscillator but all circuits I\`ve tried have terrible mains hum after demodultaion. The oscillator is tuned by capacitive sensor but I\`m using a fixed capacitor instead until I solve this problem. I\`ve tried different topologies: Franklin, Clapp, Vackář, Hartley at different frequencies from 60 to 500 MHz but there\`s no difference between them in terms of mains hum. I\`m using an SDR receiver for demodulation, it works fine and cannot be the source of hum. Using battery instead of AC supply didn\`t help. I`m using 10 µF and 10 nF capacitors for decoupling. Using physically smaller inductors helped a little, but the noise is still unacceptable. As suggested in comments, I\`ve tested all circuit nodes with and without powering the circuit and 50 Hz component appears only at the antenna output. Here are some PCB drawings, maybe there are mistakes in routing?  Fig. 1: Vackář topology, the transistor is BF545C  Fig. 2: Franklin topology, both transistors are ATF-38143 [UPD:] Uploading my setup and schematics as requested. The setup is just an SDR receiver and the oscillator with a piece of wire at the output as a makeshift antenna. The capacitive sensor C<sub>var</sub> is absent, as I\`m using a fixed capacitor C<sub>4</sub> instead.    [UPD2:] SNR at 50 Hz is 4.3 dB. Maximum frequency deviation for Franklin oscillator is 290 kHz, output power is 7.8 dBm, received signal level is –26 dBFS. Grounding the laptop makes no difference.