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RF setup

Linear - Circular conversion

All Mopra receivers produce linear polarizations. These are converted to circulars through tunable hybrids. Generally only the C-band need to be tuned (when changing between 6.7 and 4.8 GHz).

IF cabling

Rcp and Lcp from IF#1 comes from the equipment room on cables C13 and C31. IF#2 comes down cables CC11 and CC13 (Rcp and Lcp respectively).

These are normally connected directly to DAS1 and DAS2. Historically for Lcp only experiments one had to re-cable Lcp (ie C31) to DAS IFP#1 input. However depending on the experiment this is probably not required and a suitable “disko” channel selection can be used.

Coherence test/test tone

There is a remotely accessible CRO now. This has notes been tested, but Tasso and Chris have some notes on how to access this over the network

To test coherence, you need to inject a test tone 5 MHz above the lower band edge first IFP channel. For the normal 16 MHz “vsop” profiles this means injecting a tone 3 MHz below the tuning frequency. Use mmdrive to turn on the test tone:

Log onto bigrock as observer and run

> mmdrive

Set tone frequency

> w:2 freq <freq>

Set power level (typically -20 to -10). Higher frequencies (e.g. 8 GHz) need more power.

> w:2 rflvl <level>

Turn tone on

> w:2 rfon

Look at the CRO in rack F(??). Input one is connected to the 5 MHz reference from the maser and is used as a trigger. Input two should be connected to DAS monitor port XXX, which should contain the test tone you have injected. If the system is coherence, you have got the right frequency and the band has the connect inversion (ie right DAS profile, you should see the test tone 5 MHz locked to the 5 MHz.

Turn tone off

> w:2 rfoff

When observing remotely, it is still worth turning the test tone on (at a lower power level) and recording some data and checking it is visible at the expected frequency using fauto.

lbaops/mopranotessetup.1227490321.txt.gz · Last modified: 2015/12/18 16:39 (external edit)