The attached plot shows the response of the 4 new style VCOs that are present at LHO. The data is taken from the test report.
S2101407 is not like the others and has a significantly lower tuning sensitivity. Looking at the readback of the voltage applied to the actual VCO, it seems to be a property of the VCO itself and not the driver electronics.
| Serial Number | Slope (kHz/V) | Fit (x in Volts, Units in MHz) |
|---|---|---|
| S2101407 | 167.0 | 79.2779 + 0.167011 x + 0.000155672 x^2 + 0.000356935 x^3 - 0.0000487197 x^4 |
| S2101408 | 230.0 | 78.9103 + 0.229953 x - 0.000913676 x^2 + 0.000374417 x^3 - 0.0000807709 x^4 |
| S2101409 | 238.9 | 78.9922 + 0.238869 x - 0.00120282 x^2 + 0.000354021 x^3 - 0.0000857415 x^4 |
| S2101410 | 234.3 | 79.0014 + 0.234257 x - 0.00153765 x^2 + 0.000313228 x^3 - 0.0000645739 x^4 |
One thing to note is that the tuning offset on the VCO medm screen is a factor of 2 lower than the analog tuning input at the rack (or as measured by the CTRL output of the common mode board).
The high frequency gain is a factor of 25.97 smaller than the DC gain with nominal poles and zeros at 1.5292 Hz and 39.72 Hz, respectively.
Unit S2101408 seems to be installed for the IMC, see alog 63900.
Unit S2101407 is probably installed at the FC green path, since it is the only unit with a compatible low tuning sensitivity, see alog 66281.
The IMC calibration measured in alog 65175 needs to be multiplied by 2 when applied to IMC_F.
Indeed, The FC green VCO is SN S2101407.