| 摘要 |
A method of detecting an electrical device searches for an RF signal containing sidebands that is emitted from the electrical device. The RF signal is a continuous wave signal that has a known carrier frequency, e.g. from a local oscillator within the device, and a sideband at a known frequency offset from the carrier frequency, e.g. due to the power supply frequency of the device. The method comprises receiving an RF signal; downconverting the received RF signal to a baseband signal, according to the known carrier frequency; squaring the baseband signal; calculating a frequency spectrum of the squared baseband signal; and checking the frequency spectrum for a peak corresponding to the known frequency offset. The RF signal may be unintentionally emitted from the electrical device even when it is not intentionally transmitting. The frequency spectrum may be calculated by a Fourier transform. |
