Technical equipment: ANARESAT

I’ve had a couple of requests from fellow technicians to do a show-and-tell on the equipment I maintain down here.  For the first of the series, I’m going to show you our ANARESAT equipment.  I made this decision based on the sun coming out and making the ANARESAT dome look more photogenic than usual today!

ANARESAT is the name for the Wide Area Network (WAN) connection between Casey, Davis, Mawson and Macquarie Island stations, and the Australian Antarctic Division (AAD) head office in Kingston, Tasmania.  The first dish was the one here at Davis, which was installed in 1987.  The link supports VoIP, science data, a Bureau of Meteorology link, and general intranet and internet for everyone on station.

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The most prominent part of the system is the radome.  We have a 7.3 metre dish with an automatic tracking system.  The dome itself is made from multiple shapes of slightly different dimensions, and each is covered with a special high-strength laminate that is capable of withstanding 300km/h wind gusts (and the flying rocks that tend to accompany such winds).

We have a pair of Low Noise Amplifiers (LNAs) in the back of the dish with both online at all times but only one actually used for data.  They’re both carefully aligned to ensure they’re within 1dB of one another, so if we ever have a failure we have the spare online and receiving.

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These are our main equipment racks.  The left-most rack contains our VM farm, WAE, Domain Controller and other IT-related stuff that I’ll cover in a subsequent technical post.  This week we’re looking at the two racks on the right.  Though some of the equipment has been updated recently, the two racks were installed in the 80s when the ANARESAT was commissioned.  As you’ll see in a moment, some of the equipment is more than 25 years old and still working well.

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Seeing as I’ve started with the receive path, the next devices in the chain are the up/down converters and the modems.  They’re all set up in pairs and will automatically fail over to the online spare in the event of a failure, with the exception of needing to physically move the serial data cable going into the online modem.  There’s nothing stand-out about the config on these, and they’re reliable and relatively easy to work with.

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Also in the receive path is our Mitec beacon receiver.  This is a dedicated receiver for the beacon frequency transmitted by the Intelsat satellite (often called the ‘bird’) we’re on.  It’s used to give a precise signal level to the tracking system, which it uses to make minute adjustments to keep the satellite dish centred on the bird.

The one unfortunate thing about this piece of equipment is its propensity to change signal level as its temperature changes.  When the room is a constant temperature it isn’t a problem.  Recently, however, we’ve had some problems with the heating and ventilation system that has seen the temperature in our building change by a few degrees in each direction occasionally.  This is enough to change the apparent beacon level by a couple of decibels, which in turns has triggered warnings about the beacon level being too low or too high.

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The blue box towards the bottom of the photo is the Antenna Tracking and Control Unit (ATCU).  Internally it’s a relatively simple device, but it’s also an effective one.  When it is first started, you simply peak the satellite dish manually, then instruct the ATCU to perform a ‘cold start’.  It then starts drawing boxes around the satellite to determine exactly where the peak signal is.  It repeats this process periodically and forms a model of how the bird moves throughout the day, and over many days.  Once established, this model is robust enough to ensure the satellite is tracked accurately, even during a solar outage.

Towards the top of the photo is the Codan Solid-State Power Amplifier (SSPA).  There are two of these in the system, though the spare is kept offline and must be switched over manually in the event of a failure.  We’re typically putting out around 25W of power from these.  Interestingly, the signal level doesn’t drop at all during blizzards.  Unlike heavy rain, heavy snow has little effect on the signal.  It makes a nice change from dust storms and tropical rain!

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Here’s the waveguide switch used to change which SSPA is able to transmit.  In the rear of the enclosure you can see the dummy load that the spare SSPA is redirected to should it be set to transmit accidentally.

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Above is the rear of the waveguide switch enclosure, and also the dehydrator unit used to keep the waveguide pressurised with dry air.  It was made 30 years ago and, with some parts having been replaced over time, is still doing the job well enough.  Fortunately the air down here is so dry that the desiccant lasts for years without needing to be dried.

 

Thanks for taking the time to read a little about the equipment I look after down here.  I hope I’ve given just enough detail to satisfy my fellow techos without being too lingo-heavy.

Another thing I’d like to show you, while you’re here, is the midday sun.  The sun now rises after smoko and sets again before dinner.  Here’s a photo of the Sleeping and Medical Quarters (SMQ) with the sun at solar noon.  It’s quite low in the sky and stays that way for its entire time above the horizon lately.  We’re only a couple of months away from it not rising at all!

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