OBST> FESET /DEFAULT /HARM <harmonic value> /MULT <Gunn mult. value> /IF <IF frequency> /PL <PL frequency>
FESET sets up the frontend parameters for a line observation with Doppler tracking. It selects the harmonic used, the Gunn multiplier value, the sideband and the IF frequency.
The synthesizer formula used is: Sky_freq = (HP_synthesizer*HAR1 + PLL)*MUL1 +/- SIF1
where HAR1 is the OBSINP harmonic value (default 9), MUL1 is the OBSINP Gunn multiplier (default 4), SIF1 is the OBSINP IF frequency (default 1500 MHz), and the phase lock loop reference frequency is PLL. The +/- is chosen by the sideband setting in OBSINP (SID1 U or SID1 L). Sky_freq is automatically calculated by CONTROL based upon the rest frequency (OBSINP's SCF1) and is displayed on the SDH screen (``SKY_F'').
ADVERBS:
EXAMPLE:
This sets the harmonic value to 9, the Gunn multiplier value to 4, and the IF frequency to 1.5 GHz. These values are used by FEORGA to calculate the values needed for PLL and HP_synthesizer. It adjusts both because the PLL synthesizer has higher frequency resolution than the HP synthesizer (10 Hz vs 1, 2, or 3 KHz) and has a smaller multiplier. PLL is restricted to the range CPL1 +- RPL1 (OBSINP variables; defaults 105 +- 10 MHz). The value of HP_synthesizer is only changed when PLL would fall outside this range. When HP_synthesizer is changed it is set to a value which would center PLL in its range. If RPL1 is set to zero, PLL will be kept nearly equal to CPL1. (It will still be adjusted slightly in order to more accurately produce Sky_freq given the coarser settings of the HP.) The PLL synthesizer can be tuned from 90 to 120 MHz. FEORGA calculates a new synthesizer setting at the beginning of each subscan. It will do so even if only the bolometer is being used for the observations. Since there is no feed back from the HP synthesizer, one can power it off without FEORGA noticing. However, should HOST4 (the receiver roomPC) fail to accept the commands, FEORGA may abort the observation. To prevent this, turn off the FE button on the control panel.