FIRSTLO

FIRSTLO gives the LO sum for each baseband channel for all mixes other then the one that will be set if FREQ or DOPPLER is specified. For most stations, this is for use by SCHED  only; it is not written to the output file. However for stations that use VLBA control files, but are not proper VLBA stations, it will be written in a parameter that passes the information to the logging and correlator systems so that they can figure out the observing frequency. Please see FREQREF for a discussion of required parameters. If a value is not specified for a channel, it will be set to the first. Since most observations use the same firstlo for all channels, it is usually only necessary to specify one.

For the VLBA: For frequencies below 16 GHz this is just the front end synthesizer as specified by SYNTH. For 1 cm, it is the sum of synthesizers 2 and 3. For 7 mm, it is the sum of synthesizer 1 and 3 times synthesizer 3. For 4 mm, it is the sum of synthesizer 1 and 6 times synthesizer 3. At 90cm the value should be -500.0 MHz to make any frequency calculations come out right; that mix is an up-convert.

For the VLA, use the following equations:

20, 6, and 1 cm

-- FIRSTLO = F1 + F6 + 900 + FA - 600

4 and 2 cm

-- FIRSTLO = F1 - F6 - 900 - FA + 600

7mm

-- FIRSTLO = F1ab - F1cd + F6 + 900 + FA - 600

For the BD VLA channels, substitute 800 + 2*FB for the 900 + FA where:

F1 = VLAFEAB(LS)*1000 for VLA A and B channels.

F1 = VLAFECD(LS)*1000 for VLA C and D channels.

F6 = VLASYNA(LS) for VLA A and C channels - not rounded.

F6 = VLASYNB(LS) for VLA B and D channels - not rounded.

FA = FLUKEA(LS) AC Fluke setting.

2*FB = FLUKEB(LS) BD Fluke setting (usually FA + 100).

F1ab = VLAFEAB(LS)*1000, F1cd = VLAFECD(LS)*1000

If the VLA frequency parameters are set, SCHED  will calculate the FIRSTLO that will be provided by these frequencies and compare it with the FIRSTLO given by the user. If the match fails, SCHED  will complain and abort. SCHED  also checks that each synthesizer setting conforms to the rules required by that piece of hardware.

If FIRSTLO is not specified, SCHED  will try to determine it from the frequency catalog. This should be the usual case.

• Argument: An array of frequecies in MHz.
• Options: Any valid LO sum.
• Default: Will set based on the frequency catalog. If channel 1 is set and others are not, the others will be set equal to channel 1.
• Usage: Defaults to previous station.
• Example: FIRSTLO = 2400, 2400