Beam Position Monitors (BPMs)BPM hardware is described in the SPEAR 3 BPM Development web page by Jim Sebek. Use of BPMs in fast controls and history buffers is described in SPEAR Fast Controls by Till Straumann.
Local Oscillator for Bergoz BPMsAn external local oscillator (LO) using an Agilent 8647A Synthesized Signal Generator drives the Bergoz electronics. Frequency and amplitude settings have been tuned:
The first goal is to set the LO frequency to exactly 13 revolution harmonics below the RF frequency (fRf = ~476.316MHz). So fLO = (fRf/372)*(372-13) = 459.670548MHz. But when using this frequency, the Bergoz electronics had non-linearities that beat back into the measurement bandwidth. The LO bandwidth, which Bergoz accepts without a loss in performance, was measured to be something like 100kHz, so from that constraint, the LO frequency should be within the span of 459.571 to 459.771. It should be at least 4kHz away from the exact desired LO and even further to insure that it doesn't beat the synchrotron frequency (~10kHz) into the measurement bandwidth.
Setting Value Frequency 459.70158 MHz Amplitude* 12.0 dBm
The signals from the generator go out to two amplifiers in B116 and B132, respectively. They require a certain power input as specified by Bergoz. The power provided by this amplitude setting was measured to insure its proper value. Most of these systems that use LOs, in this case, Bergoz, have some +/-1dB range in which the performance does not change and will work with some reduced performance over even a larger range. The signal generator displays an error message ("008 Amplitude unspecified above 10 dBm") which can be ignored.
After a power-cycle, the "RF On/Off" button must be pushed on the signal generator.
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Contact (Content): Jim Sebek
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Last Modified: May 19, 2006