VLAFEAB is the VLA front end synthesizer for the A and B IFs (RCP). VLAFECD is the VLA front end synthesizer for the C and D IFs (LCP). See the discussion of the parameter FIRSTLO for more details. If specified, a ``//LO'' card will be written, and VLAFECD, VLASYNA, and VLASYNB will also be required. Note that, except at 7mm, VLAFEAB must be the same as VLAFECD -- there is really only one synthesizer.
Allowed values for the front end synthesizer are (in GHz) (this list was extended downward for 1 and 2 cm on 2004 Aug 27 after consulting with Ken Sowinski):
For 90 cm: 0.0
For 18-20 cm: -3.2
For 6 cm: 0.0
For 4 cm 11.8, 12.2, 12.4, 12.8, 13.0, 13.4,
13.6, 14.0, 14.2, 14.6, 14.8, 15.2
For 1 and 2 cm: 15.1, 15.2, 15.4, 15.5, 15.7, 15.8, 16.0,
16.1, 16.3, 16.4, 16.6,
16.7, 16.9, 17.0, 17.2, 17.3, 17.5, 17.6,
17.8, 17.9, 18.1, 18.2, 18.4, 18.5, 18.7,
18.8, 19.0, 19.1, 19.3, 19.4, 19.6, 19.7,
19.9, 20.0, 20.2, 20.3, 20.5, 20.6
Note that many of the above settings will not produce usable signals.
After conversion by one of the above frequencies, the upper sideband is kept at 90, 18-20, 6, 1.3 cm bands and the lower sideband is kept for the 3.6 and 2 cm bands. The resulting IF should fit within the 6 cm receiver band of 4500-5000 MHz (actually a 4355 to 5145 MHz filter). See VLASYNA and VLASYNB for more frequency constraints based on allowed values of the L6 synthesizer.
At 7 mm, VLAFEAB should be 3 times a valid value for the 1/2 cm synthesizer. VLAFECD should be a valid 4 cm value. The first value (51.6 is a typical one) will produce a lower sideband IF in the 4 cm part of the spectrum which is then fed to the 4 cm frequency conversion system.
Note that, if any of FLUKEA, FLUKEB, VLAFEAB, VLAFECD, VLASYNA, VLASYNB, VLAIF, FEFILTER, or VLAROT are specified, both LO and FI cards will be made. In such cases, any other parameters allowed to default will be set to the standard value for the specified VLABAND.
FEFLITER can be provided in the frequency catalog.