Matteo, Eleonora

We test QPD1 demodulator after adding the 12 dB attenuator on the LO path (see elog #2106) and confirmed that all the 4 channels were working fine.

We sent a LO and RF signal from DDS (-6 dB both). LO was at 78 MHz and RF was at 78MHz + 100 Hz. We could correctly seeing a signal at 100 Hz after the demodulation, shifted by 90 deg in the I and Q output. (see pic).

We tested other offsets (from 1 Hz to 10 kHz). For all these values demodulated signal has a constant amplitude fase offset between I and Q is always ~90 deg. We verified this for all the 4 channels.