LBA
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Configurable BackendAt present there are two remotely configurable backends at Mt. Pleasant. The original device (“Lovell’s Folly”) is due to be sent to Ceduna in the near future. The newer version (“Palfreyman’s Folly”) has finer attenuation control and also supports using the S/X as inputs to the DAS. Using the remotely configurable backendThe configurable backend allows for remote selection of polarisations from the multifeed receiver and IF level adjustment into the DAS. It has a crude text-based interface and can be started from newsmerd with A screenshot of the folly interface is included below. ![]() The script is menu based - enter n.b - the “DC Input” menu should always show “External SLD”, otherwise no system temperature measurement are possible. There is an internal SLD for broadband power measurements but using it would require updating the Tsys scripts, etc to use its programmable attenuators. The “DC attenuation” can also be safely ignored. Possible problems
========Lovell’s Folly information continues below here ========= A new remotely configurable backend (better known as “the Folly”) has been installed at the Mount Pleasant observatory. It is mounted in Rack 2, beneath the Drive PC breakout box. It is composed of a set of 4 RF switches (in a panel marked “4-CH. 2-WAY SWITCH”) and another module which includes programmable attenuators (with an extra 1 dB step), a square-law detector (SLD) with DC out as well as RF out. Using the remotely configurable backendThe configurable backend allows for remote selection of polarisations from the multifeed receiver and IF level adjustment into the DAS. It has a ncurses-based interface originally built by Jamie Stevens. It currently resides on newsmerd as The state of the programmable attenuators and RF switches is indicated with either an Polarisation selectionThe table below shows show the RF switch positions control which the polarisations go into the DAS. This assumes that the backend if connected normally.
The last two switches of the follow should always be set to OUT (X). Possible problems
![]() Old (and horribly verbose) info belowA new remotely configurable backend has been recently completed and installed at the Mount Pleasant observatory. It is mounted in Rack 2, beneath the Drive PC breakout box. It is composed of a set of 4 RF switches (in a panel marked “4-CH. 2-WAY SWITCH”) and another module which includes programmable attenuators (with an extra 1 dB step), a square-law detector (SLD) with DC out as well as RF out. The first pair of RF switches is used to select inputs to the backend - the default is a choice between the two polarisations of the multifeed with LCP/RCP in channels 1 and 2. An alternative is to use the RF switches to choose between the multifeed and S/X receivers. The second set of RF switches selects the input to the sampler from either the output of the SLD in rack 3 (i.e, the usual configuration) or the from the SLD in the backend itself. This allows for either wide-band continuum observations (using the remotely configurable backend) or narrow-band observations using the output of the frequency translator. The suggested set up for the backend is shown below. ![]() The default is for all the switches to select the left-hand signal path which gives RCP/LCP in channels 1 and 2, and uses the output of the frequency translator as an input to the sampler. With remote receiver selection now possible (by using STOAT within the vnc session Using the remotely configurable backendThe remotely configurable backend has a ncurses-based interface originally built by Jamie Stevens. It is still being developed (as of 26/8/09) and currently resides on newsmerd as A screenshot of the folly interface is included below. The state of the programmable attenuators and RF switches is indicated with either an Folly interface using the built-in SLD The left-hand power level is slightly higher than half, indicating a DC level of −3dB while the right-hand power level is centred, with a DC level of −4dB. The built-in SLD and 1dB step are not fully usable for flux monitoring or Tsys measurement at this time. Changes need to be made to the samutils library and the observing software to support their automated usage. Updates as events warrant! At present, the configurable backend is of most use in allowing remote changes to the observer receiver, frequency and signal level, removing the need for local assistance. |