Where O’ Where has My Calibration File Gone?

Corsair — Fri, 03 Apr 2009 07:26:35 +0000

It would appear that in the past week, something has happened to the Calibration .cat file I have been compiling for the equipment. Namely, it has dissappeared and in its stead is a string of garbled text. If anything, this serves to remind me that constant backing up and duplicating of documents is an essential part of any scientific undertaking. Interestingly, before the file went missing, a 25 point scan of the sun produced a (semi)-nice, (semi)-round representation of the Solar Disk. After attempting a 25 point scan post-calibration loss, I was greeted with no less than six suns, and a strongly emitting “V” of th 21cm wavelength spectrum.

A 25 point scan is a simple 5×5 grid of bins that are interpolated about the sun’s position in the sky. By using half beam-width bins to map across the sun in two dimensions, we can acheive a rudimentary contour graph of the intensity of the 1419.75 MHz emission line that eminates from our local star. This is purely useful as a calibration tool, as a correctly calibrated machine should produce a perfectly round disk of evenly spaced intensities. Unfortunately, I did not manage to capture an image of the mythical 6-star system that my first readings suggested we exist in, however below is a comparison of an uncalibrated system with a quasi-calibrated system that was aquired six hours into the reconstruction. As can be seen, the Pre-Calibration 25-Point scan shows two coherant sources plus noise, while the Post-Calibration 25-Point scan shows a single (and expected) coherant source with poor pointing.

25-Point Scan Pre- and Post-Calibration

After recompiling the srt.cat and tweaking parameters, I have managed to tighten the 25-point solar scan to a single coherant signal, however the pointing is still off-centre and the shape of this circle does not do justice to the greater circle community.

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Operations Safety

Corsair — Sat, 07 Mar 2009 11:35:35 +0000

I Was perusing the SRT Manual once again today and wrote a simple script to simulate a 24 hour scan of the sky directly above the dish, allowing the rotation of the Earth itself to scan a path. As I was wondering about writing more complicated scripts that would automate the SRT over a period of 24 hours or more, I came to realise an oversight. If the automation script is set to slew the dish at preset times (UT or LST) then there is a good chance there will be significant movement of the dishes during University opening hours. As such, there should be adequate signage to alert anyone on the observation deck that the SRT dishes may move without warning during operation. Whether the signage be permanent and broad in nature, or specific and able to be deployed only during use; there should be some way of warning people not to stand near them while they are in operation.

Additionally, when running extended automation scripts, 6 hours or longer in length, it is unlikely the operator will be present for the entire time (unless the operator is particularly diligent, or has little better to do with his/her time). As such, it would then be astute to assume that one might not foresee potential damage to the devices while running unsupervised. This reiterates Dr Hotan and my prior assessment, stating the need to belay the loose cables and clear the deck of detritus. I must endeavour to find out how the Control programme responds to interference with the SRT movement. If there is no back-emf sensor, if the dish becomes stuck while in operation and the Control programme does nothing to stop the dish movement, then serious damage could occur.

I will explore the feasibility of a webcam to monitor the dish while either being used remotely, or monitoring while an extended script is running.

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Syzygy » Musings

Where O’ Where has My Calibration File Gone?

Operations Safety