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Default settings for tied-array VLBI

General

These defaults are designed to cover standard Mk3 observations. Nonstandard observing includes the following, which are not covered here :

Dipoles

For observations now dipoles should be parallel (mode "22", ++). During the phase zero determinations they should be crossed (mode "21", +x) to allow easy determination of the X-Y phase differences. These are usually stable for several days, but can be different at different frequencies.

Control codes

Here are octal control codes in use at present (oct95). These do vary from time to time so the user should see the WSRT online documentation on the program STFMA. See here

PRFLAG
001012 normally and 021030 for {wideband} 92cm. Some bits are not critical.

Recent (oct98) tied array without phase switching used 001012.

STUURC
163277 or 163267. Some bits are not critical, but do not deviate from these settings without checking with the Friend of VLBI

Recent (oct98) tied array without phase switching used 023033.

DEVCO
In order to get the frequency direction right there are two settings of the RFDS (Residual Fringe Demodulation System, see NFRA note 472 and Note 478)
DXBIT
000000 (DXB is not used)
RECON
000025

Other codes

CONF.NR
70 (normal DCB)
POLC
22, parallel dipoles during observing, but can be 21, crossed dipoles for setup and checking the X-Y phase difference. See the WSRT User Documentation

with MFFEs only code 22 is possible as the dipoles do not rotate.

PROJECT
999 (for adminstration)
TYPE
VN
FRSEL
377 377 (all DCB bands used)

Mk3 Mixing scheme

See memo V#0032.MEM by Bregman

General

Because of the fixed cabling and the specific ASTI frequencies (105,130,155 and 180MHz) the centres of DCB bands always come into the Mk3 IF at certain frequencies, provided the IF/Pol select box has the mixer set to 285MHz: 

DCB band                Mk3 IF freq
                        /MHz
B3 F4                    98.75 (reserve)        [105-6.25]
B7 F8                   111.25                  [105+6.25]
B2 F3                   123.75                  [130-6.25]
B6 F7                   136.25                  [130+6.25]
B1 F2                   148.75                  [155-6.25]
B5 F6                   161.25                  [155+6.25]
B0 F1                   173.75                  [180-6.25]
B4 F5                   186.25                  [180+6.25]

Note that the 8MHz usable bandwidth allows us to have VC settings only from 4MHz below to 4MHz above these values, and that we must also account for the width of the lower sideband for frequencies below (modes A and B only) and the width of the upper sideband for frequencies above these central values.

Polarization

The normal astronomy convention is that IF1 has left circular polarization (LCP) in the `NOR' input and IF2 'normal' input has right circular polarization (RCP) in the `NOR' input. The circular polarizations are created from the input linear polarizations in the IF/Pol Select box. The connection of IFs and video converters is shown in the Mk3 rack diagram.

Video Converter settings

Assuming standard 2MHz bandwidths and the normal continuous frequency coverage (with two VCs per DCB band for modes A and B), the video converter settings come out as follows for 6, 18 and 21cm. All frequencies are in MHz: 

mode    A       A dual  B       C dual  E
VC
 1      134.25 134.25 134.25    134.25 134.25
 2      109.25 134.25           134.25
 3      138.25 138.25 138.25    136.25 136.25
 4      113.25 138.25           136.25
 5      146.75 146.75 146.75    138.25 138.25
 6      121.75 146.75           138.25
 7      150.75 150.75 150.75    144.75 144.75
 8      125.75 150.75           144.75
 9      159.25 159.25 159.25    146.75 146.75
10      175.75 159.25           146.75
11      163.25 163.25 163.25    148.75 148.75
12      184.25 163.25           148.75
13      171.75 171.75 171.75    150.75 150.75
14      188.25 171.75           150.75

At 92cm where we have never used the full bandwidth, and only used 7 video converters (mode E) we use one DCB band per video converter. The video converter is centred on the DCB band and the DCB bandwidths are all set to 5MHz to minimize overlap. This gives 

mode                                    E
VC
 1                                      111.25
 3                                      123.75
 5                                      136.25
 7                                      148.75
 9                                      161.25
11                                      173.75
13                                      186.25

For convenience (and possible future dual polarization mode C observing) even video converters should be set the same as the odd video converter below, i.e. VC2=VC1, VC4=VC3 etc.

Different wavebands

Each different wavelength will also have its own individual frequency and bandwidth setups. See section Tied-array setups per wavelength

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