Hang Tivo Daniel

We resurrected the 72 MHz WFS chain and locked in DRMI. Since we don't have harmonics generators yet, we are using ifr signal generators. We started with the modulation set at 13 x 9.1 MHz and the demodulation set at 8 x 9.1 MHz + 205 Hz. Using a double demodulation technique at 8 x 9.1 MHz + 205 Hz (RF) and 205 Hz (digital) we should be able to derive WFS signals for the SRM. However, we noticed that before the digital demodulation the line at 205 Hz was highly variable in amplitude, plus we saw stable harmonics at 410 and 615 Hz. These lines stayed after we turned the 13x modulation off! Meaning, there is a contamination due to higher order intermodulation products from our main modulation drives. As a consequence, we switched the scheme to use an 8 x 9.1 MHz demodulation and 13 x 9.1 MHz + 205 Hz modulation. This eliminated the contamination due to higher order intermodulation products and produced a clean line at 205 Hz before the second digital demodulation. At 410 and 615 Hz no lines were visible anymore. As a result we were able to cleanly lock the PLL to the 205 Hz line of the WFS sum and demodulate individual WFS segments.