The DBBCs have 4 conditioning modules (CoMos). Each CoMo can take up to 4 input IFs and one of these can be selected to pass through an analogue Nyquist filter. The CoMo also contains an IF amplifier and variable attenuator to get the signal level correct for digitisation.
Nyquist filters are selected by filter number. For the AuScope DBBCs they are all 512 MHz wide but for newer DBBCs they are 1024 MHz. Filter numbers for AuScope:
1: 512 - 1024 MHz 2: 0 - 512 MHz 3: not used 4: 1024 - 1536 MHz
Our S-band LO is 1900 MHz so all our S-band signals are passed through filter 2. X-band LO is 7600 so we either use filter 1 or 4.
The three AuScope DBBCs have four CoMos. Here is a diagram of how the IF inputs are set up.
On the AuScope DBBCs the signal from each CoMo then passes through and ADB1 and Core2 board. Each of the Core2 board acts like 4 BBCs, producing USB and LSB bands of 4, 8 or 16 MHz bandwidth each. So for standard R1/R4 IVS experiments, we require 6 S-band channels and 8 X-band, Mostly USB but a few USB and LSB. Our X-band LO is such that 4 of the BBC frequencies fall into the range of Filter 1 and four into Filter 4. So our usual setup is as follows:
1. X-band_RCP -> CoMo_A input 1, filter 1 -> Core2 with four lowest BBC frequencies 2. X-band_RCP -> CoMo_B input 4, filter 4 -> Core2 with four highest BBC frequencies 3. S-band_RCP -> CoMo_C input 2, filter 2 -> Core2 with four lowest BBC frequencies 4. S-band_RCP -> CoMo_D input 2, filter 2 -> Core2 with two highest BBC frequencies
To configure the DBBC there are a set of commands to set up the CoMos, and another set to configure the BBC frequencies. These are documented in the DBBC manual, but as an example, our standard geodetic mode is as follows:
define ifdsx 13073181521x ifa=1,agc,1,40000 ifb=4,agc,4,48000 ifc=2,agc,2,35200 ifd=2,agc,2,35000 lo= lo=loa,7600.00,usb,rcp,1 lo=lob,7600.00,usb,rcp,1 lo=loc,1900.00,usb,rcp,1 lo=lod,1900.00,usb,rcp,1 enddef
For the IF settings, the first column in the IF input to select (and what IF is at what input is station-specific), 'agc' refers to automatic gain control which is the default (it could also be 'man' for manual), the next column is the filter number (depends on what four BBC freqs you want) and lastly the target DBBC power level. This is station specific too. All those “lo” settings are cosmetic as far as I can tell
At the moment, drudg uses skedf.ctl to get default DBBC IF inputs (“if absent from schedule file”) and seems to work out which filters to use. It doesn't know what power levels to use and we have to put them in to the procedure file by hand.
Drudg will also produce a (e.g.) dbbcsx8 procedure which sets up the BBC frequencies
define dbbcsx8 13073181521x bbc01=612.99,a,8.00 bbc02=652.99,a,8.00 bbc03=752.99,a,8.00 bbc04=912.99,a,8.00 bbc05=1132.99,b,8.00 bbc06=1252.99,b,8.00 bbc07=1312.99,b,8.00 bbc08=1332.99,b,8.00 bbc09=325.99,c,8.00 bbc10=345.99,c,8.00 bbc11=365.99,c,8.00 bbc12=395.99,c,8.00 bbc13=445.99,d,8.00 bbc14=465.99,d,8.00 enddef
It's pretty obvious what these mean. The second column refers to which CoMo to use but it actually doesn't do anything as this isn't configurable in a DBBC!
How these BBCs are mapped out to the VSIs (which sideband and to which of the 16 output channels) is determined by the 'form' command (same as 'dbbcform' in the DBBC manual). The two we use are 'geo' and 'astro'. The Mark5 mode is also set up in the setupsx procedure. This is usually done correctly for geodetic experiments but we hand edit for LBA.
define setupsx 13073181521x pcalon tpicd=stop mk5b_mode=ext,0x55555555,2 mk5b_mode form=geo form dbbcsx8 ifdsx cont_cal=off tpicd=no,0 bank_check tpicd enddef