Since we found that we cannot lock PLL, I did the test of PLL by sending signal inside and checking output signal.

The PLL servo box contains

(Before doing test, we succeed in connecting computer and servo. We also succeeded in writing a desirable command to servo.)

Input signal:

1.Beat note: (1) 20MHz Sine wave with 100Hz frequency modulation, deviation of 1MHz. (2)20MHz Sine wave with 100Hz frequency modulation, deviation of 1kHz. (see attached figure 1 and 2)

2. Local oscillator: 20MHz from DDS board.

The purpose of using these two signals is to check how PLL acts when we have a "beat note" signal deviating from local oscillator. The result is as following:

1. Close the fast control loop. Sending beat note (1) and local oscillator. We check on oscilloscope and found it almost give just an offset of 10V. If we look at the AC of this signal, there is something(20mV) and the frequency is 100Hz. So it is sensing the difference between LO and BEAT.(see attached figure 3 and 4)

2. Open the fast control loop. Others are the same with rsult 1. We found almost nothing. So this means the small AC signal we get is because of the comparison of LO and BEAT.

3. We also tried to reduce the deviation. Close the loop and send beat note (2) and local oscillator. Then we got an AC signal without a clear frequency.

Conclusion: The PLL board has a problem. Actually we did the same test when Chienming was here. At that time, the signal we get from output channel is quite large.