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SATELLITE TVRO

Satellite Television Recieve Only

[My Technical Notebook]


A VHF folded dipole construction Coaxial cable Velocity test Stacking Colinear 3 x 3/4 A Duplicated Boomer Yagi antenna for 2 m Transmission lines problems This Page
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Still Under Construction

Antenna Mechanical Construction

In 1985 the Satellite Television Receiver Only era started emerging in Indonesia, only a view people were able possessing those expensive equipment. Most were imported from USA. When I saw those system in one of my relative home, I realized that the system was not to complicated. It's consisted of a Parabolic antenna unit and a receiver unit which seemed look like an ordinary audio amplifier. For this reasons I was challenged to build my own Satellite TVRO system, I was so certain that it wouldn't cost to much. I started designing the parabolic antenna first and my handicap for this was looking for a suitable method in making an accurate parabolic curve. So its mean I must have an accurate parabolic curved template whenever I design a aluminum construction either a fiber glass molded parabolic reflector.

Di tahun 1985 Zaman TVRO mulai memasuki Indonesia, Hanya sedikit orang yang mampu memiliki peralatan yang mahal itu. Kebanyakan dimasukan dari USA. Ketika saya melihat disalah seorang kenalan saya, saya berpendapat bahawa semua perlengkapnya tidaklah terlalu rumit. Terdiri dari unit antena parabola dan sebuah alat penerima yang nampak seperti pesawat penguat suara biasa. Dengan ini saya merasa tertantang untuk membuat sendiri sistim TVRO tersebut, dan yakin biayanya tidak akan semahal sistim yang diimpor. Saya mulai merancang antena parabolanya lebih dahulu dan satu-satunya kendala adalah untuk memperoleh cara membuat kurva parabolik secara teliti. Ini berarti saya harus mempunyai pola kurva parabola baik untuk merancang dengan konstruksi aluminium maupun dari bahan fiber tercetak.


Parabolic Reflector

Fig 1

Any signal coming straight perpendicular through the aperture will be maintain reflected by the parabolic reflector to the focus point, this means the sum of the distance from the aperture level to the reflector and from the reflector to the focus point will be always equal at any point the signal came in straight upright at the reflector aperture. a1 + bn = a1 + bn

Base from this Formula I made parabolic curve sliding cutter as shown in Fig2 and 2A for making the parabolic curved template. In designing the sliding cutter, I determined first the focus to diameter ratio for an optimum performance. A 0.28 FD ratio was determined. 2 small pulley was installed one at F (Focus point) and the other at the sliding bar C. A steel wire (Usually use for vehicles brake wires) was fastened at pole A (Aperture point). An electric drilling machine was fastened at D (parabolic surface point) which will moved whit a distance A - D when the sliding bar SB is pushed in the cutting direction.. A load for maintaining the wire remain straight was put hanging down at the end of the wire. The wire length A-F and F-D is equal to a1 + bn I used a 5 mm milling machine tip and adjust the drill speed by a speed controler for the best cutting result.

 

Parabolic Curve sliding cutter

A= aperture level point
F = focus point
D = Drill
SG = sliding guide.
SB = sliding bar
TEMP = template material
Fig 2

Fig 2 A

Setiap isyarat yang masuk tegak lurus melalui mulut/celah ke permukaan akan selalu dipantulkan ke titik fokus oleh parabola. Ini berarti jumlah jarak dari celah permukaan ke reflektor dan reflektor ke titik fokus akan senantiasa sama disetiap titik. a1 + bn = a1 + bn. Berdasarkan rumusan ini saya membuat alat pemotong pola kurva parabola seperti tampak di Fig 2 dan 2A. Lebih dahulu ditentukan perbandingan fokus dan diameter sebesar 0,28 agar diperoleh unjuk kerja yang optimum. 2 rol kecil digunakan satu pasang di F (Titik fokus) dan satu di C Di balok SB. Seutas kawat baja (biasa digunakan pada rem sepeda motor) di ikat di A (Titik garis masuk) ke rol F terus ke mesin bor di pasang di D (Titik permukaan). Bor akan bergegeser antara D-A bila balok SB didorong kearah pemotongan. Sebuah beban di gantung diujung kawat untuk mengatur agar kawat selalu dalam keadaan tegang. Panjang kawat baja dari A-F-D adalah sebanding dengan a1 + bn. Pisau scrap 5mm digunakan untuk pemotongan dan kecepatan bor diatur dengan pengatur kecepatan agar diper oleh hasil potongan yang terbaik.


Fiber Glass construction

fig 3 Mold

fig 4 Fiber glass layer

Antenna Bracket asembly

My plan was building a 2.8 meter Disc, a mold was made of clay using the parabolic curved template see fig 4. The template was turned slowly at its shaft above a heap of clay until an evenly smooth surface and an upside down parabolic mold was formed. After that I put on the top a small molded aluminum disc made from graphite sand casting by YC1COR, this part will function as antenna pool mechanism bracket and feed horn mast bracket. A thin layer of fiber glass resin was applied onto the mold surface, attached above it with thin aluminum foil, covered with another resin layer and above it a fiber glass matting covered with resin . Several mating layer was applied until it's rigid and thick enough.

Rencana saya adalah membuat antena parabola berdiameter 2,8 meter. Sebuah cetakan di buat dengan pola kurva parabol lihat fig 4. Pola diputar perlahan pada asnya diatas setumpuk tanah lempung sehingga terbentuk permukaan yang halus merata dan sebuah parabol terbalik. Setelah itu saya letakan sebuah piringan kecil ditengah atas yang dibuat oleh YC1COR dari aluminium cor cetak pasir, bagian ini akan berfungsi sebagai pegangan untuk mekanisme tiang dan tumpuan tiang feedhorn. Kemudian selapis tipis resin fiber glas di ulaskan diatas cetakan, padanya dilekatkan aluminium foil tipis, lalu dilapisi dengan tikar fiber glas. Lapisan tikar fiber di tambah sampai ketebalan yang cukup dan kekokohan diperoleh.

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A VHF folded dipole construction Coaxial cable Velocity test Stacking Colinear 3 x 3/4 A Duplicated Boomer Yagi antenna for 2 m Transmission lines problems This Page
Page 2 of 4


Updated March 2000.-