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Pages: 1

C Band service in Afghan

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Ex Member
Ex Member

Jan 8th, 2010 at 10:00am  
A client of mine is asking us to quote for C band inclined orbit service, Bandwidth is obviously cheap but the issues of maintaining a 4.5 meter tracking Antenna are not for faint hearted, also C band is getting lots of issues with interference, any views on whether this is a relaible solution ?
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Eric Johnston
Senior Member

Posts: 2109
Reply #1 - Jan 8th, 2010 at 11:00am  
I like the expression "not for the faint hearted".  Dead right!  Installing and operating an outdoor 4.5m tracking antenna, to work to an inclined orbit satellite, really does require significant local expertise to get working properly in the first place and to keep operating afterwards.  The azimuth and elevation angle encoders or resolvers suffer from ice, insects, birds, corrosion... The motors and gearboxes, in intermittent use every few minutes, need oiling, greasing, cleaning and suffer fretting damage due to frequent forward/back movements over a small range.  The motor control electronics is unusual and dangerous.  The tracking control computer requires great skill to set up and configure so its software model matches the hardware characteristics.  The RF side needs to be linear so the shape of the main beam matches the computer model. I recommend a proper CW beacon receiver, which has a much larger dynamic range, than a modulated traffic carrier (e.g. CDM570, iDirect etc) receiver to do the tracking.  A proper beacon receiver is also not affected by uplink rain fading.  Despite everthing you will still lose service from time to time, get locked to a sidelobe, wrong satellite or simply wander off somewhere. Make sure you have on-site spares for resolvers, motors, motor electronics and tracking controller and all the tools, handbooks and circuit diagrams.

I know the above sounds depressing but it is better you appreciate the problems before, rather than later.  If you have experience of tracking antennas you will understand and laugh. If you have no experience, then maybe think again.

Inclined orbit capacity is cheap because of the above problems.  If you cost the project over say 12 - 18 months (typical residual lifetime of inclined orbit operation of an end-of-life satellite) total up the monthly satellite costs, monthly earth station maintenance and the capital costs and compare total overall costs.

You mention C band operation.  Be aware that C band operation is increasingly interfered with from new licenced/unlicenced terrestrial WiFi services and that this has made C band almost unuseable in many cities. This interference can sometimes be mitigated by using higher C band frequencies and special microwave filters in front of the LNB.

Sorry to be so gloomy but it snowed yesterday and it's freezing cold here.


Best regards, Eric.
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« Last Edit: Jan 8th, 2010 at 12:57pm by Eric Johnston »  
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