Wednesday, 21 May 2008

Identifying Satellites In A Crowded Sky

Crowded satellite sky’s over India is causing unique technical issues whilst aligning dishes for the DTH providers.
With the booming DTH market and the lack of bandwidth it has caused additional problems for the DTH provider apart from the rain fade problems during monsoon period.

As more and more DTH providers are launching satellites service in India, the lack of available bandwidth is causing big problems to align the small DTH dishes to receive the satellites. In addition to the normal problem with dish installations like rain fade during monsoon period simply to identify the right satellite during installation is difficult in India. 
Currently we have the main DTH satellite placed only 3.50 apart. So with traditional methods to find the satellite and aligning them, it’s virtually impossible. Dish TV is using NSS6 at 95.5o East, Both SUN Direct and DD Direct are using Insat 4B at 93.5o East and BIG TV is using Measat 3 at 91.5o East. It means that the actual installer will find these satellites / services simply by moving the dish 5 mm. This is an extremely small movement to identify these satellites. So if he is using a RF meter or a simple satfinder he will more or less pick up a signal for all three together rather than 3 distinctive signals. Thus he will not easily be able to identify them. He will have to verify the satellite by hooking up a set top box. Then he might discover if he is on the right satellite or not. Even if he does this, he will not be able to peak the dish for trouble free reception during the monsoon period. If he on the other hand is using a costly spectrum analyzer he again will have trouble to identify the individual satellite or peaking them. It’s possible with a spectrum with built in NIT (Network Identification Table) reader, to identify the satellite but the three signals of equal high strength will interfere with each other. 
It’s the same situations we face in radio tunings. At some places there might be two or three very close stations. Its’ difficult to tune to them and we might not know which station it is until we can hear news or announcements. 
What can be done to easily find the correct satellite, and peak it for least problems during the monsoon period?
Maxpeak, manufactures a unique range of Satmeters, SAM and SAM-lite. Our approach is simply to quickly and easily identify the correct satellite and then enable a quick peaking of the dish.
Both are preprogrammed for the correct satellite data stream and will only lock onto the correct satellite. As both have built in MPEG receiver they will read the digital signals rather than RF level. This means that when they have locked onto the correct satellite, we can measure Carrier to Noise ratio, Modulated Error Rate and most significantly pre Bit Error Rate (before Forward Error Correction). Peaking the pre BER makes the search extremely fast and responsive. Moreover if there is modulation error and / or noise these are picked up quicker and with a greater range by the pre BER. We then repeat simply the whole process by reversing the pre BER into a Quality bargraph to peak the dish. This is done in % and 98 % means there is 2 % of error in the digital signal.
SAM is the full version and SAM-lite has been especially designed for emerging markets like India. Both are the same in ease of use and accuracy but SAM-lite has a lower cost and less features. Both have been designed for Indian conditions, like higher ambient temperatures and high humidity and more demanding mains voltage conditions. In addition we have opened our own subsidiary in New Delhi, to cater for local technical support and sales and marketing.

Source:
http://cablequest.org/articles/dth/item/1411-identifying-satellites-in-a-crowded-sky.htmlSource: http://cablequest.org/articles/dth/item/1411-identifying-satellites-in-a-crowded-sky.html

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