This is a summary of the changes made Jan 16-18,1998. The changes allow one to observe with Frontend #2 or both #1 and #2. Also the name of the AOS command has been changed to BACKEND, and you can now specify the Backend by name. -Bill The new BACKEND command works just like the old AOS command. You can still specify which backends to use by specifying their numbers. Or you can specify them by name. In order of backend numbers 1-8, they are: DRUM, HOLO, AOSA, AOSB, AOSC, NASA, FBS, and CHIRP. The only difference between Frontend #1 and Frontend #2 is the synthesizer used: #1 specifies the synthesizer frequency of Synthesizer #1 and #2 specifies Synthesizer #2. (Currently, only the SIS490 uses synthesizer #2.) FEORGA checks which frontends are in use and sends the appropriate synthesizer setting(s). Which frontends are "in use" is selected by specifying which frontend is associated with each active Backend. The active backends are specified by the BACKEND command. The associated frontend(s) are specified through the new BE_FE command: BE_FE [] where is the backend name or number, and is the frontend number. The second is used only if the can be connected to two Frontends simultaneously. (This is currently only possible for DRUM.) BE_FE also prints out the current Frontend associations for each backend. (Type it with no parameters to just see this output.) Repeat BE_FE for each Backend whose associated Frontend is to be changed. (Note that the old scheme of specifying the Frontend by the /RECEIVER adverb no longer works.) The RX command has also been changed so that one can specify which receiver is connected to each Frontend. The /R_NAME adverb now takes up to two parameters: the name of Frontend #1's receiver and the name of Frontend #2's receiver. For example, RX /R_NAME SIS230 SIS490 The RX command also sets up the Harmonic and Multiiplier for the Gunn for each receiver (via the FESET command). To specify that only Frontend #2 is to be changed by the RX command, use * for the name of Receiver #1. (To only change Frontend #1, either omit the Receiver #2 name or use an * for it.) When specifying the rest frequency, one should use the /RECEIVER adverb with the LINE command (and specify either 1 or 2, as appropriate). As usual, if /RECEIVER is omitted, the default value is assumed. Temporarily, one can only verify what the LINE and FESET parameters are in effect for a particular Frontend by doing SHOW FE1 or SHOW FE2 in OBSINP. When two frontend's are being used, the pointing model receiver offsets used are determined by a new OBSINP parameter, PMOD. If it is zero, the offsets for the receiver named in the lowest numbered active Frontend is used. A 1 specifies FE1 and a 2 specifies FE2. (But if the value specifies an inactive frontend, the lowest active Frontend is selected.) There will eventually be an OBST command to select this and print the name of the receiver being used for the offsets. POINTING commands with two frontend's in use is similar to when one uses the two-channel SIS345 receiver: The continuum data for both frontends is recorded in the Raw Data, but only the Drumbeat channel selected by the DISPL_CHAN command is processed and recorded in the Pointing data base.