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Tuning in to satellite T\T, Pt.2 This month, we take a look at the satellites that are visible from Australia and discuss the hardware requirements for C an'd Ku-band reception. We also include a few tips on aiming the dish. By GARRY CRATT The most popular C-band satellite amongst satellite TV enthusiasts is Intelsat 5, located at 180E 0 • This satellite, or "bird" as they are often called, carries links from the USA for several commercial television networks in Australia, as well as one transponder for the US Armed Forces Radio and TV Service, Cable Network News (CNN), and some French programming for the Polynesian islands. These transmissions are not made to any published schedule, although most are at regular times. They are not intended for reception by commercial organisations other than the transponder lessee. The material transmitted is also copyright. However, the amateur satellite enthusiast will find the reception of these programs most interesting, both from a technical point of view and from a contents point of view. No licence is required to receive this information, provided the material is not used for commercial purposes and the copyright is preserved. Table 1 shows the C and Ku-band satellites visible from Australia. To receive Intelsat and the other Cband satellites, the minimum dish size required to produce acceptable results is 3.5 metres. With a dish this size plus a good LNB having a noise temperature of less than 50°K, and by using "threshold extension" techniques such as narrow IF filters, it is possible to produce entertainment quality pictures and sound. However, there is no performance margin when using such a (relatively) small dish, and so signals are likely to deteriorate as the satellite ages or during periods of heavy rain. A larger dish will provide more gain and give some performance margin above threshold, thus allowing some headroom. As transponders are leased to customers, performance and programming can change dramatically from year to year. For example, transponders using a hemispherical beam can be switched to a lower intensity global beam, thus resulting in a weaker signal. In addition, satellites can be moved or even replaced in time, so any deci 0 sion to establish a satellite TV system must be based on the knowledge that reception cannot be guaranteed long term. However, experience has indicated that the use of satellites as a delivery method for TV programming is becoming more popular as time goes by, so reception from at least one satellite should always be possible. Signal coding There is also a growing trend for transponder lessees to use some method of encryption to scramble satellite signals, in order to protect sensitive material from interception. On the Intelsat satellites visible from Australia, several commercial TV net- Basic Scheme For An Aussat Ground Station MONITOR LNB RECEIVER 00 O Cl 18 SILICON CHIP D Fig.I: to set up a ~round station, you need a dish, a low-noise block (which is mounted on the dish), a receiver & a TV monitor. The LNB provides frequency conversion to the first IF (1450-950MHz) & these signals are then converted by the receiver to a second IF at 70MHz. works use a system called "vidiplexing". This system is not really encryption in the true sense of the word. It allows more efficient use of a transponder (or half transponder) by mixing two video frames together, each from a different source. Separating the two video signals is quite a simple matter and is easily done by using a video monitor which has been turned on its side, so that the two frames can be displayed vertically. This also involves rotating the yoke 90°. Fig.2 shows this technique. An inexpensive b&w set or computer monitor can be used for this purpose .. However, in spite of the growing trend to scramble transponders, there is still plenty of satellite activity which uses no encryption at all and is unlikely to ever do so. The Aussat system For the reception of Ku-band satellite signals in Australia, Aussat is really the only signal source available. There are three Aussat satellites in orbit at present, providing an interesting mix of program material. To establish a Ku-band system, capable of good results, the minimum dish size is considered to be 1.5 metres. This allows the reception of usable pictures from the low power (12 watt) transponders. The Aussat satellite system comprises three satellites: Aussat 1 at 160°, Aussat 2 at 156°, and Aussat 3 at 164°. The services carried on these satellites are listed in Table 2. Aussat carries three systems for delivering television. The first is a DBS (Direct Broadcast Service) which utilises B-MAC as the transmission mode. This system is based on propdetary technology, devised by Scientific Atlanta in the USA and licensed to Plessey Australia, which produces B-MAC receivers locally. B-MAC signals are supposed to provide superior video and audio reception, compared to the standard PAL system. These signals can only be received by authorised B-MAC receivers. The transponders used for this service are high power (30 watt) and good results can be achieved using a 1.0 or 1.2-metre dish. Unfortunately, the cost of a B-MAC receiver (which will also receive PAL signals) is quite high, at around $2000, and without one, no intelligible pictures or sound can be received. It is Table 1: Satellites In ITU Region 3 Satellite Country Location Band Statsionar 13 USSR 80° East C-Band DFH2-A1* China 87.5° East C-Band Statsionar 6 USSR 90° East C-Band lnsat 1C India 94.5° East C/S or C/Ka Band DFH2-A3* China 98° East C-Band Statsionar-T USSR 99° East UHF Asiasat* China 105.5° East C-Band Palapa B1 Indonesia 108° East C-Band BS-2B* Japan 110° East C-Band DFH2-A2* China 110.5° East C-Band Palapa B2P Indonesia 113° East C-Band Palapa B3 Indonesia 118° East C-Band Superbird A* Japan 128° East Ku/Ka Band CS-3A* Japan 132° East C/S or C/Ka Band CS-3B* Japan 136° East C/S or C/Ka Band Statsionar 7 USSR 140° East Ku/Ka Band JCSat 1* Japan 150° East Ku-Band JCSat 2* Japan 154° East Ku-Band Aussat A2 Australia 156° East Ku-Band Aussat A1 Australia 160° East Ku-Band Aussat A3 Australia 164° East Ku-Band Intelsat V F3 174° East C/Ku-Band Intelsat V F1 177° East C/Ku-Band Intelsat V F8 180° East C/Ku-Band *N ot visible from Australia unlikely that the B-MAC encryption system will ever be broken by software hackers and there is little reason for anyone to attempt to do so. This DBS system was designed for installation as a consumer product in rural areas and operates a regular published program service. High quality audio (stereo) programs are also carried. The RCTS service The second system carried by Aussat is a regional distribution service for TV stations around Australia. This systems is known as RCTS, or the Remote Commercial Television Service. Some commercial networks use the RCTS system to transfer program material interstate to their own studios. These links are generally scrambled, using a system called E-PAL. In this scrambling technique, the video signal is inverted, the sync removed, and the audio signal is inserted into the vertical blanking area. Considerable circuitry is required to unscramble E-PAL and, because all program material is subject to copyright, there is little point in expending any effort to decode these signals. There is, however, another service carried on Aussat which is unscrambled and of significant interest. This JULY 1991 19 is the "news interchange" service , and is designed to allow regional Earth stations to recover news items for inclusion in local news programs. Much of this information is broadcast in the form of pre-edited news items, ready for video editing. However, there are also many hours of direct un-edited programming re-broadcast (after standards conversion) by Aussat Master Control from the Intelsat 4GHz service, from which the programming originated. Typically, services such as CNN, Skynet, BBC World News and many others can be received in the course of any 24-hour period. Of course, this programming is often interrupted by local news event coverage, transmission of promotional material, and test patterns. In fact, there is sufficient unencoded program material broadcast to justify the establishment of a ground station, the cost of which can be kept to less than $1000, as we shall see. You can now afford a satellite TV system For many years you have probably looked at satellite TV systems and thought "one day". You can now purchase the following K band system for only $995. 00 This is about 1/3 the price of comparable systems Here's what you get: • A 1.8 metre pressed steel prime focus dish antenna, complete with all the mounting hardware - as well as a self supporting ground stand. • One super low noise LNB (low noise block converter) l.4dB or better. • One KU band feedhorn and all the mounting hardware as well as a magnetic signal polariser. Radio programming • 30 metres oflow loss coaxial cable with a single pair control line. In addition to TV services, Aussat also carries radio programming from Radio Australia, the ABC and one commercial network. The Department of Aviation also uses the satellite system for air to ground communications, particularly in remote areas. All these services use SCPC as the transmission mode. So when all three satellites are considered, there are many • A 99 channel infrared control satellite receiver with adj ustable IF and audio bandwidth, polarity, and dual digital readout. The IR control unit has a range of approx. 10 metres. Before you receive your system the unit is pre-programmed to the popular AUSSAT transponders via the internal EEPROM memory. This unit is also suitable for C band applications. services of potential interest to enthusiasts. Selecting the hardware Having decided to procure an Earth station, it is important to select the correct hardware. Whether the decision is made to build a C-band Earth station or a Ku-band station, the receiver that is used is common to both systems. Basically, the receiver converts a block of frequencies from 9501450MHz to "baseband" signals, comprising video and audio. This process is common to both C and Ku systems. Apart from the cable that feeds the receiver from the LNB, this is where the hardware similarity ends. For starters, the C and Ku bands use LNBs with vastly different frequency characteristics. Also, due to the frequencies used, the size of a suitable dish is much larger for C-bahd than Ku. Note that in all instances , a larger diameter dish will provide better results, as will an LNB having a lower noise temperature. Aiming the dish Assuming that the correct combination of hardware has been selected, the next step is to determine where to locate and point the dish. Because the locations of both the satellite and the proposed Earth station are known, a mathematical calculation can be made to determine the necessary dish elevation and azimuth. Fig.3 shows a CALL, FAX or WRITE to AV-COMM PTY LTD. PO BOX 386, NORTHBRIDGE NSW 2063 PHONE (02) 949 7417 FAX (02) 949 7095 All items are available seperately. Ask about our low noise 'C' band LNB, and other interesting products. All systems are provided with dish pointing details. ----------- 1 Yes Garry, Please send me more information I on your K band satellite systems. I Name ........ ....... ... ........ ........ ... .. I I Address .............. .... ... ..... .. .. .. ... I ................................................... I ........................... P/Code ........ . . I I Telephone .. . . . . . . . . .. .. .. . . . . . . . . .. . . . . . Ii, ~N= ~ !:. - 20 - - - - SILICON CHIP -0= I I I I I I I I I .I Fig.2: vidiplexed signals can be separated by using a video monitor which has been turned on its side & its yoke rotated by 90°, so that the two frames can be displayed vertically. A b&w monitor is best used for this purpose. A typical satellite receiver is shown next to the monitor. · Table 2: Aussat Services Transponder Polarity Satellite (Aussat 1,2,3) Programming Coding 1 V 1 Network 9 EPAL 9 H 1 Network 9 PAL 2 V For lease 10 H DOA, Aussat Data 3 V 11 H 4 V 1 Network 10 PAL 12 H 1 ABC PAL 5 V 1 SBS BMAC 13 H 3 1 2UW/Macquarie SCPC 1 Network 7 EPAL Q Net ABC Radio 6 V 1 Network 10 EPAL 14 H 1 2 ABC HACBSS Skychannel BMAC BMAC 7 V 1 ABC HACBSS BMAC 15 H 3 Network 9 PAL 8 V 2 ABC HACBSS BMAC BASIC computer program that can be used to calculate these parameters. Alternatively, most satellite hardware suppliers will provide the "pointing" information on request. Only two tools are necessary to enable you to accurately point the dish: a magnetic compass and a protractor. A compass is necessary to find the direction that corresponds to the correct azimuth. Note, however, that there are "lines of magnetic variation" crossing the Earth's surface, and these variations must be taken into account . when using the "heading" that has been mathematically calculated. For example, the magnetic variation for Sydney is -11 °. This means that 11 ° must be subtracted from the calculated azimuth heading. The easiest way to set up a dish is to set the ele·v ation first. This can be done by using a protractor, a length of cotton and a weight to measure the angle of elevation (this can be done from the back of the dish). Once the elevation has.been set, the dish can be manually turned (ie, the azimuth adjusted) until a signal is received. Obviously, this alignment procedure will be much easier if all receiving equipment, including the video monitor (or TV set), is temporarily . located next to the dish. Another method of alignment is to use a receiver that has been pre-tuned to the correct satellite channels, or to use a receiver fitted with a "scan" facility. By connecting a digital voltmeter across the receiver signal strength meter, the slight increases in signal strength which occur as the dish is moved closer to optimum alignment can be used as a pointing aid. This technique can also be used to align the feedhorn and to optimise the LNB probe rotation, prior to fitting any polarising device. Motorised drive If reception from more than one satellite is required, a motorised drive system can be employed. In this instance, a mechanical adjustment for the angle of declination must be built into the dish mount, to compensate for the location of the Earth station. In greater detail, all satellites pur- sue a circular orbit but this orbit is with reference to the equator. As the Earth station location gets further from the equator, the satellites appear to be in an elliptical orbit and so cannot be tracked by simply rotating the dish. This problem can be corrected by building a mechanical compensation into the dish mount. A far simpler system, considering the relatively small number of satellites viewable from Australia, is to mark both elevation and azimuth on the dish mount and mounting pole with an indelible marker for each satellite. The dish can then be manually adjusted whenever a different satellite is required. Once the dish is mounted, the LNB can be affixed to the feedhorn and polarotor if used. In the case oflntelsat reception, the feed can be configured to LHCP (left hand circular polarisation), or to RHCP in the case of the Russian Gorizont satellites. If building a Ku-band Earth station to view Aussat, a feedhorn capable of selecting either polarity (vertical or horizontal) will be necessary. Note that mechanical polarity changers have significant losses (as SATELLITE ENTIIUSIASTS! • • 1.5M Dishes complete $445 High performance Ku Band Hemt LNC's 2 yrs warranty.. $370 • Complete B-Mac Systems .. $2895.00 • Complete C Band Systems • Dishes Small through to Large • Pal Receivers ... $595.00 • Complete range of cables, connectors and accessories Call now for FREE Catalog, Information Bulletin and SPECIALS .. (02) 489 5474 Videosat Pty. Ltd. 83 Alexandria Pde. Wahroonga ' NSW 2076 [ ~VIDEOS~Ilj Fax (02) 489 3557 Mr/Mrs/Ms ...................................... . Address ......... ................................... . Telephone ....................................SCj ul91 * For all your Satellite Needs - Nationwide * JULY1991 21 will be the case if any object is placed in the feedhorn). Electronic polarity changers using the Faraday effect technique have far less losses and hence offer considerable advantages over their mechanical counterparts. The cable used to connect the LNB to the receiver should be a low-loss 75-ohm type. RG-59 or, better still, RG-6 or RG-11 is preferred, although air-dielectric copper and aluminium wrap braided UHF TV coaxial cable can be used in some cases . However, cheap cables with solid dielectric and single copper braid will not work at all over significant distances. Type "F" connectors are universally used to terminate the cables. In addition, steps should be taken to weatherproof the LNB cable connection. This can be done by using a rubber spark plug cover, as commonly supplied by auto accessory shops. These rubber boots form a snug fit over the cable and connector on the LNB. A non-acid based silicone sealant (neutral cure, as sold for metal roofing) should be used around the seal between the cable and the boot. Because a polarity changer is necessary for a fully equipped Ku-band system, special coaxial cable which contains two separate conductors (one to feed the control voltage) should be used. Typically, these special cables are available in lengths of 30 and 50 metres. This dual function cable will greatly simplify the installation of a Ku-band system. Australian suppliers of satellite equipment cater mainly for commercial Ku-band installations or remote area C-band systems. They can be found in the Telecom Yellow Pages in most capital cities. Most are able to supply and install equipment almost immediately. Next month, we will take a look at a complete ground station that you can purchase for less than $1000. It comes complete with a 1.8-metre dish antenna and is ideal for tuning into the Aussat satellites. Fig.3: Antenna Pointing Program 10 CLS:PRINT 'GEOSTATIONARY SATELLITE BEARINGS FOR SOUTHERN HEMISPHERE" 20 PRINT" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -": PRINT 30 INPUT "ENTER YOUR LATITUDE IN DEGREES AND DECIMAL DEGREES (E.G. 30.855)";A 40 INPUT "ENTER YOUR LONGITUDE IN DEGREES AND DECIMAL DEGREES (E.G. 152.922)";0 50 INPUT'ENTER THE SATELLITE LONGITUDE IN DEGREES EAST ";Y 60 INPUT "MAGNETIC DEVIATION FOR DISH LOCATION (0 IF NOT KNOWN) "; MD 70 IF Y>O THEN GOTO 110 80 IF Y<O THEN GOTO 90 90 B=O-Y 100 GOTO 120 110B=Y-Q 120 C=A • .017 4533 130 D=B *.0174533 140 E=SIN(C) 150 F=TAN(D) 160 H=3.1416+ATN((F/E)) 170 AZ=H*180/3.1416-180 180 IF Y>O THEN GOTO 220 190 IF Y<O THEN GOTO 200 200 AS=360-AZ 210 GOTO 230 220 AS=AZ 230 J=(COS(C) *COS(D)) 240 CA=·ATN(J/SQR(-J* J+ 1))+ 1.5708 250 CB=CA*180/3.1416 260 R=3957 270 K=22245 280 RA=SOR((R*R)+(R+K) * (R+K)-2* R*(R+K) *COS(CA)) 290 T=((RA *RA+(R*R)-((R+K)* (R+K)))/(2*RA *R)) 300 TL=-ATN(T/SQR(-T*T+1))+ 1.5708 310 EL=(TL*180/3.1416)-90 320 RB=RA *1.609344 330 PRINT:PRINT "- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -" 340 IF EL<=5 THEN GOTO 440 350 PRINT 'AZIMUTH = ";AS;" DEGREES FROM TRUE NORTH " 360 IF MD=O THEN GOTO 380 370 PRINT 'AZIMUTH = "; (AS+(MD));" DEGREES FROM MAGNETIC NORTH" 380 PRINT "ELEVATION = ";EL;" DEGREES" 390 PRINT "RANGE = "; RB;" KILOMETRES" 400 PRINT:PRINT:PRINT "PRESS ANY KEY TO CONTINUE OR E TO END" 410 A$="" 420 A$=INKEY$ IF A$='"' THEN GOTO 420 430 IF (A$="E") OR (A$="e") THEN GOTO 460 ELSE GOTO 10 440 PRINT "SATELLITE TOO LOW .... ELEVATION IS ";EL;" DEGREES" 450 GOTO 400 460 END Example Run of Program ENTER YOUR LATITUDE IN DEGREES AND DECIMAL DEGREES (E.G. 30.855) 30.855 ENTER YOUR LONGITUDE IN DEGREES AND DECIMAL DEGREES (E.G. 152.922) 152.922 ENTER THE SATELLITE LONGITUDE IN DEGREES EAST 160 MAGNETIC DEVIATION FOR DISH LOCATION (0 IF NOT KNOWN) 0 AZIMUTH ELEVATION RANGE = 13.60957 DEGREES FROM TRUE NORTH = 53.23546 DEGREES = 36893.85 KILOMETRES Further reading (1). "Aussat Network Designers Guide" - Aussat. (2). "The Complete Guide To Satellite TV" - Tab Books. (3). "Build a Personal Earth Station for Worldwide Satellite TV Reception" - Tab Books. (4). "1991 World Satellite Alma22 SILICON CHIP nac", by Mark Long (available from Opac Pty Ltd, 99 Boundary Rd , Peakhurst. Phone 02 584 1233). (5). "Satellite & Cable TV Scrambling and Descrambling", by Brent Gale & Frank Baylin. (6). "Troubleshooting & Repairing Satellite TV Systems " - Tab Books. (7). "The Hidden Signals on Satellite TV" , by Thomas P. Harrington & Bob Cooper Jnr. - Howard Sams Books. (8). "Ku Band Satellite TV Theory, Installation and Repair" , by Frank Baylin & Brent Gale. SC