The Big “T” Dish
4.9m diameter @ 4.9m high and operational

Two months ago JX Satellite was commissioned by Auckland’s Triangle / Stratos TV to provide a solution for the reception of Asia sat 3 @ 105.5 degrees east elevation 8 degrees  and Asia sat 2 satellite @100.5 degrees east with an elevation of 4 degrees .. Over the last year or so many new services have become available on both of these satellites that require a dish larger than 3.7 m is diameter.

Asia Sat 2 provides its own unique challenges due to the elevation angle to the satellite being only four degrees from vertical. Asia Sat 3 is slightly better with an eight degree elevation angle. New Zealand sits right on the very edge of a footprint which extends from Europe right through the Middle East, India, Asia, and the Far East down through Australia to New Zealand and some of the Pacific Islands .In all over fifty countries are positioned with in there  powerful C band coverage beams.

Asia Sat 3 S @105.0 East	Asia Sat 5 @100.5 East

            The brief was to provide a solution using as much of the existing infrastructure as possible. Space to mount dishes is at a premium in the Back garden of Triangle / Stratos. Dishes have been added over the years to cater for new satellites which provide the back bone of Triangles / Stratos programme schedule.

When they started some fifteen years ago the only satellite with any programming suitable was the old Asia Sat Satellite located at 100.5 degrees east. In those days the only programming available was VOA and the European Bouquet which both used full transponder configuration providing enough signal for it to be well received on a 3.7m dish.

That was fifteen years ago, before channel providers begun to use a myriad of broadcast configurations which include full transponder “MCPC” Multiple Channels per Carrier , “SCPC” Single Channel per Carrier utilizing both power and band width restricted operation . Varying FEC and Mega symbol rates which alter the receive “IRD” input threshold. That was before Asia Sat 2 decided to go on a Christmas break on Boxing Day in 2005 and we down here sitting on the very edge of the footprint suddenly found that  3m dishes working with these signals were now prone to signal fading . In fact the 3.7m was subject to serious signal fading which made it unsuitable for a lot of the new channels that Triangle TV had broadcast rights for.

JX satellite undertook a feasibility  study of Triangles requirements , the channels it wishes to receive , High on the priority list  was  D/W TV , Not the original D/W TV which could be received but the new D/WTV designed exclusively for the Asia /Pacific region.

It was decided to run with the largest dish 4.9m which would provide the reception required and would fit the confined space where Triangle TV’s dish farm is located. This just happens to be where the old 3.7m dish was located some 5m high over looking the surrounding houses.

So JX Satellite decided that a 4.9m Comstar AZ/EL antenna would best suit Triangle TV’s varied reception requirements. This antenna would be one of the best larger antennas suitable for commercial reception of varying broadcast formats.

Commercial antennas of this size cost many many thousands of dollars and normally require purpose built mounts and concrete pads .in our case we had to modify the 5m high mount that supported the outgoing 3.7m. An additional challenge was to not block Triangles Micro wave link to the Auckland transmission site some 50 Kms away.

The Dish arrives

The dish arrived in two wooden crates, the first housed the ribs, and the outer ring the inner rings and the mesh. The second housed the hub and the mount plus all the nuts bolts and rivets.

The whole dish was unpacked and an inventory taken of all the parts. It was soon discovered that an inner ring was missing. An email to the supplier confused the issue even more. As it turned out the dish originally had sixteen ribs and the revised version now has twenty ribs making it more stable and rigid.

Building and skinning.

The building took place at Triangle TV due to the sheer size of the dish. The first step was to place the Hub on a suitable elevated surface. In our case it was a well used Saw horse. We attached the ribs one by one until all twenty ribs were bolted on making the structure look like a giant star fish.

Next came the first spacer inner ring which was bolted into place. The second spacer ring was added which made the structure more rigid. Then came the small spacers near to the hub these pulled the ribs very tight on the hub.

The last part of the overall assembly was the outer ring which then completed the dish structure. The over all parabola was very rigid now waiting to be skinned.
We started off from the center point and placed the first panel on the rib assembly. Each panel had to be trimmed before they were fixed by a long alloy strip which had to be drilled and pop riveted through the rib assembly .Each rib had twenty rivets plus another ten to secure the mesh to the struts and cross members.  The outer ring which also held the mesh was the last to be riveted into place providing us with the skeleton dish as can be seen from the photos.

The attachment of the very fine mesh panels took quite a lot of time as they had to be placed on the rib structure and timed to the exact size so that the alloy retaining strip would hold it down as well as the one next to it as well. We started in a clock direction ending up right along side the panel we first started with.

The reflector was completed just as Peter arrived with the cherry picker

Mounting the dish 5m high

Before we could mount the new 4.9m we had to firstly take down the aging 3.7m Orbitron.

Considering that the Orbitron had been sitting 5m up in the air since Triangle launched fifteen years ago it was in surprisingly good shape .however getting it off the mount 5m up was a different story . However hard we tried the mount would not release.
So in the end we took out four panels which is also not the easiest perched 5m up with the winds starting to build up.

We ended up lashing the top half reflector to the cherry picker cradle and POP off it came. No trouble what so ever and we gently placed it on the ground with out damaging any of the panels.

Next came the big lift, two strops were placed through the center of the dish and using a criss cross bracket system and several ropes positioned around the ribs we started to lift .At one meter off the ground we attached the mount to the hub and set it in such a way that it could be maneuvered into position.

With every one standing at there positions we slowly lifted the beast sky wards. Three meters off the ground all was looking good .We lifted up to approximately six meters ready to float the mount on the pole when out of no where the wind got up and started gusting. The effect was immediate the whole structure started to yaw wildly and if it wasn’t for the quick thinking of the ground crew it would have knocked me off the top of the pole .and probably wrecked the dish completely. So that was it for Sunday, we all went home slightly disappointed that we were almost there only too be thwarted by the elements.

Monday

5 am and the alarm clock rang, the day was as still as could be. Arriving at Triangles Studio it was heartening to see that some of our installer friends from other companies had also got out of bed in the middle of the night to be there to help. This time there was no wind and with in twenty minutes the dish was sitting on top of its 5m pole.
Then came the turn of the engineer who was to modify the mount by adding another four retaining bolts to the mount and attach some bracing which would stop a lot of the wind judder.

The only criticism I have for the whole dish which is a dream to build and mount even 5m high, is the lack of thought put into the LNB mount. It is the most stupid, mount ever devised by man. It doesn’t fit any standard LNBF.The focal point is adjusted by long threaded rod which attaches to the Scalar ring .However it’s so long that no LNBF can sit in the scalar ring and be adjusted.

However with a little help from an angle grinder we managed to make the LNBF fit. We will change this by cutting the four feed support rods and riveting alloy dowel in them and cutting the rods until we are near to the focal point “1.96m “ so that we can use a one cable solution LNBF. We will also mount a second LNBF onto this feed support system so that we can also receive Asia sat 3 s located at 105.5 degrees east as well using the secondary focal point .

Finding the signal was quite easy considering the size and the height we were working at. Some twenty minutes later, up popped the carriers of Asia Sat 5 with signal strengths for full transponders in the region of 12 db CNR. Why only 12 for a full transponder. Given the fact that 99% of the transponders required have IRD thresholds of approx 5.2 Db CNR and that at FOUR degrees elevation, signal fading occurs even trees some miles away which you think would never interfere with the signals . They do and as any one knows who has worked with big dishes and low elevation angles it’s an entirely different situation.

Today Euro News was peaking 68 % signal quality and was providing a superb picture as was France 24, the European Bouquet R/R Sat, Globe Cast and the EU feeds. So against all the odds and the weather the installation was a total success.

                    

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