Table of contents
- 1. Frequency setups
- 2. Setup for 4 Gbps
- 2.1.1. DBBC Setup
- 2.1.2. Fila10G Setup
- 3. ALMA Mode 4 Gbps (fullband mode)
- 3.1.1. DBBC2 setup
- 3.1.2. FILA10G setup
Frequency setups
The standard GMVA frequency setup is used for more than 90% of all observations. Other setups which are listed in the VLBA table of setups for the 86 GHz receiver are possible though, but not all stations may be able to tune to all the LOs given in that table.
Setup for 4 Gbps
In this mode 32 channels of 32 MHz from the PFB will be used. 16 channels for each polarization. To avoid the complications by the tracklistin the flex mode it would be preferred to observe this part using the basic "dbbcform=spol" mode. This requires the IFs to be connected to the last two Core2Boards. As we need this for the ALMA Mode below as well this should not be an issue for this test. If necessary at all stations need to recable any how.
The configuration is then quite simple:
DBBC Setup
dbbcform=spol
All data from the last Core2Board (presumably IFD) will be send to VSI1 and all from last-1 (presumably IFC) to VSI2.
Fila10G Setup
splitmode off inputselect vsi1-2 vsi_samplerate 64000000 reset vdif_frame 2 32 8000 reset
This will produce a joint 64 bit stream with the first 32 bits from VSI1 and the second half with 32 bits from VSI2. If the correlator prefers to have alternating channels we would also need to command the permutation matrix from below.
regwrite chan_perm 0 0x21200100
regwrite chan_perm 1 0x23220302
regwrite chan_perm 2 0x25240504
regwrite chan_perm 3 0x27260706
regwrite chan_perm 4 0x29280908
regwrite chan_perm 5 0x2B2A0B0A
regwrite chan_perm 6 0x2D2C0D0C
regwrite chan_perm 7 0x2F2E0F0E
regwrite chan_perm 8 0x31301110
regwrite chan_perm 9 0x33321312
regwrite chan_perm 10 0x35341514
regwrite chan_perm 11 0x37361716
regwrite chan_perm 12 0x39381918
regwrite chan_perm 13 0x3B3A1B1A
regwrite chan_perm 14 0x3D3C1D1C
regwrite chan_perm 15 0x3F3E1F1E
reset
After all the settings have been done, the Fila10G needs a timesync from FMSET or in case of an internal GPS a manual fila10g=timesync.
ALMA Mode 4 Gbps (fullband mode)
For ALMA compatibilty the DBBC2 stations must observe in fullband PFB mode covering the full 512 MHz per polarisation in a single IF channel. The mode is quite simple, as written below one just need to command "dbbcform=full", but there is not much flexibility about the input IFs as for other observing modes. All data from the last Core2Board (presumably IFD) will be send to VSI1 and all from last-1 (presumably IFC) to VSI2. There is no option to choose something else.
DBBC2 setup
It is recommended to restart the DBBC PFB control software, if it was used in another mode (SPOL or FLEX) before setting the fullband mode. Reprogramming might not be necessary. Of course reprogramming is required if the DDC mode was used before.
The only option to be commanded is
dbbcform=full
The 2bit digitalization threshold is fixed in this mode and optimization of the bit statistics is done most easily by adjusting the input counts using the IFx commands. To check the bit statistics short recordings can be analyzed with m5bstate. Detailed instructions provided By Gino Tuccari can be found here.
FILA10G setup
To combine the both VSI streams it is usually enough to set the Fila10G to:
splitmode off inputselect vsi1-2 vsi_samplerate 64000000 reset vdif_frame 2 2 8000 reset
However, this will join the two steams to a single 64 bit stream one after each other VSI1 bit 0-31 and VSI2 bit 32 to 61. The correlator expects to have alternating bits from channel 1 and 2. VSI1 bit 0+1, VSI2 bit2+3, ....
This can be forced with the following changes of the channel permutation matrix:
regwrite chan_perm 0 0x21200100 regwrite chan_perm 1 0x23220302 regwrite chan_perm 2 0x25240504 regwrite chan_perm 3 0x27260706 regwrite chan_perm 4 0x29280908 regwrite chan_perm 5 0x2B2A0B0A regwrite chan_perm 6 0x2D2C0D0C regwrite chan_perm 7 0x2F2E0F0E regwrite chan_perm 8 0x31301110 regwrite chan_perm 9 0x33321312 regwrite chan_perm 10 0x35341514 regwrite chan_perm 11 0x37361716 regwrite chan_perm 12 0x39381918 regwrite chan_perm 13 0x3B3A1B1A regwrite chan_perm 14 0x3D3C1D1C regwrite chan_perm 15 0x3F3E1F1E reset regupdate vdif_header 2 0x01000000 0x1F000000 regupdate vdif_header 3 0x04000000 0x7C000000
After all the settings have been done, the Fila10G needs a timesync from FMSET or in case of an internal GPS a manual fila10g=timesync.
The mode has been succesfully tested at Effelsberg (details).
