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C band Reception on small aperture Offset antennas.

Good morning Richard and a very warm welcome from Auckland where the heat wave is still with us. Our thoughts are with everyone in the northern hemisphere suffering the icy chills of winter.

Our topic this week has turned out to be quite controversial both here Australia and now it seems in the USA. What we are going to dedicate this entire segment to is the reception of high power C band signals on small aperture Ku band offset dishes.

C band reception to my self and I am sure many others begin and ends with large parabolic antenna's   normally several meters in diameter .Well times have changed and C band satellites have stronger more focused  beams than ever before .

Years ago I saw a 1m parabolic dish made in the UK working on the high powered Gorizont c band spot beam over Europe. The reception device   as previously stated was a one meter prime focus parabolic dish mounted on a simple AZ / EL mount and was mated with a 120 Degree LNA feeding a 70 MHz down converter and satellite receiver.

Why could they use such a  small dish ,and let us get the timing right here ,HBO and a hand full of channels was all that could be received in the USA  on dish sizes larger than 4m. There were no Astra's or Eutelsats , the first Anik satellite  had just been launched .In Japan high power YURI satellite tests using KU were having mixed results  due to TWT'S  failing and over in Europe  OTS   (Orbital Test Satellite ) was being readied for launch.

So how is it that ORT1 live from Moscow via a Gorizont satellite could be received on such a small aperture antenna. The answer was very simple Transponder 6 3675 was a power house generating over 44Dbw of signal which even in 1982 could be well received on a dish as small as 1m.

So lets bring this story up to date Located at 169 degrees East sits PAS 2 now called IS2 it is nearing the end of its mission life and  it is slowly dying in orbit . A lot of its traffic has been shunted over to Pas 8 IS 8 at 166 East.

 The main traffic on these satellites are distribution feed for such companies as Via Com , Turner , Discovery  Networks   being able to  distribute directly from the USA west coast  via its Napa teleport to  the Asian pacific rim Countries. This craft also carries other channel operator's distribution to the USA from Asia and around the Pacific Rim.

So Pas 2 was quite an important satellite for the Asia Pacific region. Launched in 1994 its 15 year mission life is almost over when it started misbehaving and Intelsat decided to co locate PAS5 with Pas 2 at169 East.

So how does this affect Satellite reception here in New Zealand and really revolutionize C band reception using small aperture antenna .IS5 (Pas5) has a large C band horizontal and vertical downlink coverage beam which extends from Singapore across the pacific Ocean to as far as the Pacific islands of Tonga and American Samoa covering Australia, New Zealand, Philippines, Indonesia, China, Hong Kong, Taiwan Japan   Thailand.

However the bore site or Beam center extends in a sort of figure 8 from the Philippines through Australia at Darwin and exits near Adelaide and sweeps through around New Zealand around the Fiji islands back up to meet north of the Philippines.   

This Primary footprint coverage is rated at 41.6 DBW on both Horizontal and Vertical polarities. For the first real time New Zealand has a high power C band beam covering it.

South west of New Zealand the signal drops by -2 Db from 41.6Dbw to 39.6Dbw however this level for C band power is very potent and allows the usage of small aperture antennas.

So what type of antenna can be used for this reception .One normally equates C band reception with BIG dishes, that was in the past today's generation of high powered satellites provide signals to many parts of the world in excess of 41dbw for selected services using full transponder  operation.

This is where the experiments started in Auckland and through out New Zealand late last week when IS 5 finally reached its new home and started broadcasting. Reports came flooding in of massive power increases and reception on dishes as small as 2m.

Intelsat 701 has been providing high power C band spot beam coverage to Fiji and the Pacific Islands for several years now using an offset dish and C band LNBF mated with a conical feed horn.

This was our starting point we knew that the Fiji service provided about 38 Dbw to New Zealand and that the high power Aesan beam from Palapa C2 provided about 36 Dbw of signal to Auckland.

We quickly assembled a 1.2m offset dish which had been collecting dust in one corner of the garage for several years.  

Once erected it was a very simple exercise to locate the new Signals from IS5 .for the first time Australia Network came booming in loud and clear. So the logical next step was to emulate this experiment using different types of offset dishes to see exactly what the smallest dish that could receive High power C band signals.

We started again with a stock standard 75cm Ku dish and mounted our C band LNBF at where we believed the focal point to be and sure enough one could see the carriers quite plainly .However what the problem is when using a small offset dish for C band reception is the amount of gain provided by such a small dish and secondly the amount of blockage caused by the increased C band LNBF size compared to that of a Ku band LNBF.

Actually we succeeded in loading one of the new carriers and resolving signals from it .this test gave us a very good indication of the actual signal on the ground compared to the published footprints maps from the satellite operator.

I am pleased to report that based upon my observations full transponder operation provides approximately 39 Ddw .So now we had a more accurate signal level we calculated that if we upped the size to 1m this would be more acceptable and easier to mount on roof's and walls.

So a 1m Chinese branded Ku dish was mounted on a regular unimount normally used for dish sizes 60 to 80cm. But this was a test to see what it would take for an enthusiast to build a system which would provide him with Viewable pictures on Australia Network and the BBC.

So our C band mounting bracket was bolted onto to feed arm, it is best to employ a 1m dish with side arms due to the weight of the C band LNBF over that of its Ku counter part. The LNBF was secured and the dish swung towards IS5 .Instantly carriers appeared on our Spectrum Analyzer which we disconnected and turned to the TV monitor beside us. The LNBF was then moved forward and back   and rotated slightly to provide the Best quality % on the on screen signal meter.

We averaged quality %'sin the mid 30's to early 40's and over the last week the picture has been on 24/7 with out a blemish or hick up. We took this one step further last weekend and also mounted a Ku LNBF along the arm to receive Optus D1 satellite at 156 East carrying Nz's free view service and D2 at 152 East carrying 60 channels of ethnic TV.

This increased the available channels by 100 fold, and provided the following channels;

Channel 1 TV1 NZ national channel
Channel 2 TV2 NZ national channel
Channel 3 TV3 NZ national channel
Channel 4 C4 NZ national channel
Channel 5 Maori TV Channel 4
Channel 6 TV6 NZ
Channel 7 TV7 NZ

Channel 8 Australia network
Channel 9 BBC World
Channel 10 Stratos
Channel 11 Cue TV
Channel 12 Russia today
Channel 13 NHK World
And so on.

Richard what we tested here in NZ can be utilized any where you have a C band signal higher than 36 Dbw for example in the USA the C band Equity channels provide    a signal to all of CONUS of over 40 Dbw .

I'm not saying we've broken the barriers down here in NZ but it does give food for thought doesn't it .