Frontend operations¶
General rules¶
To change the frontend Local Oscillator frequency, use the following command:
> setLO=[freq1];[freq2];…;[freqN]
Notice the semicolon. Ideally, different values could be assigned to different IFs, thus tuning each section to a different sub-band. For the TPB, though, this is not possible, so a single value must be specified:
e.g. ``> setLO=5600``
Remember that the actually observed band begins at a frequency which is usually different from the LO one (see Antenna overall setup)
For the L-P band receiver, filters are available in order to set the observed sub-band and select the polarisation (circular or linear), specifying a code with the command:
> receiversMode=[code] (see the next section for the details)
The temperature of the calibration mark in use is recorded in the logfile whenever a Tsys is measured. It is also stored in the FITS/MBFITS output files. The calibration mark can be manually switched on and off respectively with:
> calOn
> calOff
If users want to perform the setup for the frontend only (without affecting the mount, the minor servo or the backend), the command is:
> receiversSetup=[code] (PPP, LLP, PLP, CCB, KKG)
Specific notes for the L/P receiver¶
The L/P receiver is actually seen by DISCOS as a group of three different receivers, each having its own setup code:
- PPP for the usage of the P band only
- LLP for the usage of the L band only
- PLP for the dual-feed usage
These are the codes to be used in the setupXXX command. Then the configuration of the band filter and of the polarisation mode must be performed, by means of the receiversMode command. Here follows the list of options.
PPP¶
Only the P band can be used. The possible configurations are:
> receiversMode=C1XX
> receiversMode=C2XX
> receiversMode=C3XX (default)
> receiversMode=L1XX
> receiversMode=L2XX
> receiversMode=L3XX
The first two characters in the code identify the polarisation mode C = Circular, L = linear) and the band filter index, where:
- all band, 305-410 MHz (no filter)
- 310-350 MHz
- 305-410 MHz (band-pass filter)
The XX chars are placeholders for the L-band configuration, which is not allowed in PPP mode.
LLP¶
Only the L band can be used. The possible configurations are:
> receiversMode=XXC1
> receiversMode=XXC2
> receiversMode=XXC3
> receiversMode=XXC4 (default)
> receiversMode=XXC5
> receiversMode=XXL1
> receiversMode=XXL2
> receiversMode=XXL3
> receiversMode=XXL4
> receiversMode=XXL5
The last two characters in the code identify the polarisation mode (C = Circular, L = linear) and the band filter index, where:
- all band, 1300-1800 MHz (no filter)
- 1320-1780 MHz
- 1350-1450 MHz (VLBI)
- 1300-1800 MHz (band-pass)
- 1625-1715 MHz (VLBI)
The XX chars are placeholders for the P-band configuration, which is not allowed in LLL mode.
Local Oscillator for L-band observations¶
Starting from the release of DISCOS 0.6, it is possible to use the setLO
command for this receiver, in the operator input console:
> receiversSetup=LLP
> setLO=2300
This new feature is only available using the L-band feed (it is not
possible to set the LO in the PPP
configuration).
It is not allowed to set the LO inside the observed sky band. For instance:
> receiversMode=XXL5 (Bandwidth 1625:1715)
> setLO=1650
Error - Value out of legal ranges
It is also not possible to set a receiver mode in case the current LO value is inside the mode band:
> receiversMode=XXL5 (Bandwidth 1625:1715)
> setLO=1500 (Ok, it is outside the RF band)
> receiversMode=XXL4 (Bandwidth 1300:1800)
Error - Value out of legal ranges
Notice that, for this receiver, the LO frequency is higher than the
observed frequency. For this reason the bandwidth value displayed in the
Receivers
monitor is positive while the IF is negative,
indicating that the IF band is inverted. For instance, in the following case:
> receiversMode=XXL5 (Bandwidth 1625:1715)
> setLO=2300
the receiver panel will show startFreq=-675
and bandwidth=90
.
The band initial frequency can be obtained as LO+startFreq.
A 1000 MHz low-pass filter is applied to the IFs, so it is not possible to set a LO value that brings the IFs outside the range of the low-pass filter:
> receiversMode=XXL4 (Band 1300:1800)
> setLO=200 (IF band: 1100:1600)
Error - Value out of legal ranges
IF distributor¶
The SRT has a new device (IFDistributor) capable to perform down conversion and IF filtering when the
L-band receiver is configured.
The control of the local oscillator and the down conversion is transparent and can be done
as already described. In particular, all the caveats regarding the limits still hold. In case
a filtering of the IF bandwidth is required (e.g. when observing with the DFB3) the command ifd
must
be used:
> ifd=[filterid]
FILTER ID | Central Freq (MHz) | Bandwidth (MHz) |
---|---|---|
BW-NARROW | 576 | 115 |
BW-MEDIUM | 640 | 230 |
BW-WIDE | 768 | 460 |
BW-UNFILTERED | see L-Band |
PLP (dual band)¶
In this setup, both bands are used and can be configured, according to the following scheme, based on the permutation of all the previously described codes:
> receiversMode=C1C1
> receiversMode=C2C1
> receiversMode=C3C1
> receiversMode=C1C2
...
> receiversMode=C3C4 (default)
> receiversMode=C3C5
...
> receiversMode=L1C1
...
> receiversMode=C1L1
...
> receiversMode=L1L1
...