Switching from Wide band scanning observations to Narrow band pointed observations

Software

• Load the appropriate narrow band schedule (this should have instructions to select bandwidth and centre frequency different from the default values), it should also load the 8MHz config file - currently mb4mod_8

  Here's a sample sched file:

  $ unit    1
  freq = 1415.
  bandwidth = 8.
  config = mb4mod_8
  refbeam = 1
  enable refbeam
  fcc_p_trk = disabled
  fcc_rot = 0.0
  source = object7
  fitsname = object7
  cycles = 40
  raj = 12:24:07
  decj = +13:17:29
  track
  $unit   2
  .
  .
  refbeam 2
  .
  .
  $unit   3
  .
  .
  refbeam 3
  .
  .
  $unit   4
  .
  .
  refbeam 4
  .
  .
  

Hardware

• Change the LO frequency
  For the 8 MHz filter, centred at 36MHz required frequency = (Required Band Centre + 36MHz)/4 (The LO is produced by the RH Marconi synthesiser perched on top of the main Observing room equipment racks. To change to a new value, enter the setting eg 361 on the numeric keypad and press the MHz button to the right of the keypad).

• Change the Sample rate generator to twice the band width (ie an 8MHz band requires a 16MHz sample rate). The sample rate is produced by the Marconi Synthesisor next to the Multibeam correlator rack.

• Set the filter switches at the back of the filter unit (RHS on main observing rack looking from back) to the appropriate values.

• Use ATTSET (on ARTHUR) to change attenuator values to give a reasonable total power measurement. You may need to increase the gain by a factor of around 8 ie around 6dB less - however the current mb4mod_8 config file has a sample divider set to a lower value, not the best way to increase the sample power but the only option if you've run out of attenuation. (Note, if power is tto low the samplers may not lock, to check this type the command mbsam in the mbcor window. The samplers should all show o.

Switching from Narrow band to Wide band

Software

• In tkmulti's command box (bottom left) type Exit to close multi.
• Exit tkmulti
• Restart multi on ARTHUR (this will reset eveything to suitable defaults for 64MHz wide band and scanning)
• Restart tkmulti
• type enable antenna and enable fcc as usual
• Load the appropriate schedule.(Check that no ref beam number shows and the bandwidth and centre frequency are correct when running)

Hardware

• Switch back to the 64MHz filters.
  For the 64MHz filter centred at 160MHz
  
• Change the LO frequency.
  For the 64MHz filter centred at 160MHz
  Required frequency = (Required Band Centre + 160MHz)/4 (Scanning is usally centred at 1405MHz with an LO setting of 391.25MHz).The LO is produced by the RH Marconi synthesiser perched on top of the main Observing room equipment racks. To change to a new value, enter the setting eg 361 on the numeric keypad and press the MHz button to the right of the keypad)

• If using the Link Hut LO, this can only be set with a resolution of 100kHz, so a setting of 391.5 is used, giving a band centred on 1406MHz. Use the SETLO utility on ARTHUR to change the LO., and MCDSP to display the current settings.
• Change the Sample rate generator to twice the band width (ie a 64 MHz band requires a 128MHz sample rate). The sample rate in produced by the Marconi Synthesiser next to the Multibeam correlator rack.

• Use ATTSET (on ARTHUR) to change attenuator values to give a reasonable total power measurement.