MULTIPLE

MULTIPLE FEED ANTENNAS: Rediscovering An Old Idea

TORUS TYPE ANTENNA at an Intelsat grade satellite facility
                         (SANTA PAULA, CALIFORNIA)
            (Top photo showing back structure of antenna)
          (Bottom photo showing multiple feedhorn array)

Those new to the DBS arena might marvel at how great the development of the "DISH 500" and other multiple beam antennas appear to be. In all reality, it's no great invention, as the basics have been out there for years, and a short study will show that there are even better ways to extract the signals of more than one satellite from a single fixed antenna.

Sometimes it helps to look at the past when trying to re-invent the future. Most of the VIPs in today's satellite industry do not have a clue how things got started about 20 years ago. They are too busy making business deals and concerned only about the bottom line and how it applies to their personal pocketbook. There was a time not too long ago when most people in the industry had a spirit of sharing and cooperation, and we all looked forward to what next month would bring in the form of innovations in satellite equipment. These people were true pioneers, and every new development was chronicled in magazines such as Coop's Satellite Digest, STV, Satellite Retailer, to name but a few publications that are no longer around. You really had to be there, soaking it all in, and getting your hands dirty turning wrenches and having fun learning how this technology worked.

If this sounds nostalgic, you will probably enjoy some of the attached pictures, because they are from our recent past. Look at the similarities in how things are done, with regard to how signals are collected with large (mostly C-band) antennas. Rocket science is how the signals got into orbit, but there really isn't anything new in the design of how antennas collect signals.

What you see on the left of the page are the reflecting and collecting ends of a huge commercial multiple satellite antenna that is common at many Intelsat transmit-receive facilities.



		At the top of this page is a smaller multiple feed antenna known as a Simulsat, which basically is an elongated 5 meter antenna which allows as many as ten satellites to be intercepted at the same time. This particular antenna once did service at a casino in Southern California, but was donated to UCLA in Los Angeles. You are looking at it coming to rest after being reinstalled in a new location. This type of antenna is quite huge and quite costly, but when you eliminate the need to install 8 or 10 separate large dishes, it starts to make sense. Next is an 18-foot Spherical type antenna structure that was installed in a coastal Alaska village in the mid 80s. Note the distance of the three feedhorn assemblies on tripods from the main antenna. The antenna itself has an f/d ratio (focal length to diameter) of 1.25, which means the feedhorns are 18 X 1.25 feet away, or 22.5 feet in front of the antenna. The extreme distance from the reflector meant that each tripod had to be weighted with sandbags. A very interesting way of getting 3 C-band satellites at the same time. Left to right were collectors for Anik D1 at 109 West, Satcom F3 at 131 West, & Aurora 1 at 143 West. You could easily see 40 degrees in azimuth.

MULTIPLE FEED ANTENNAS: Rediscovering An Old Idea

THE FUTURE IS COMING AND IT COULD LOOK LIKE THIS: Same Paraclipse 90 cm pictured on right, but outfitted with NINE LNBFs on multi-feed bracket. Satellites received include DISH NETWORK's 61.5, 110 and 119 West birds, NIMIQ 1 DBS at 91, SBS-6 Ku at 74, GE-5 Ku at 79, GE-2 Ku for Primestar at 85, TELSTAR 5 Ku at 97, and the RCA 101 West cluster. _______________________________________________ This page shows the same concept as pictured on previous massive expensive antenna systems, but on a small scale. Welcome to the world of Ku-band and DBS (10.7 to 12.75 GHz). Antenna efficiencies can be much greater and certainly more consistent when you are using high precision stamping machinery and solid metal. The average consumer now expects (and gets) miracles with an 18-inch offset antenna married to digital electronics. What most of them do not know is that going to the 36-inch (90 or 95 cm) size that was once quite the rage with Primestar, you uncover some fascinating concepts in reception. DBS satellites are typically cranking out +54 dBW to most locations, which is an incredibly strong signal on a 3-foot dish. Add this surplus signal to the wide beamwidth of these antennas, and you can often find usable DBS signals 25 degrees to the left and right of center. Elevation angle and point of signal collection will vary up and down, but imagine this as sort of a mirror. You just need an up/down adjuster and a stable bar to attach your hardware. That is exactly what we have created here at Global Communications, and will be selling modified offset antenna systems to enable the rest of you to enjoy what we have re-discovered.		Close-up view of same Paraclipse 90cm above, showing multi-feed bracket and nine (9) LNBFs installed. The simplest system might take a favorite satellite at the center focus. This could be Telstar 5, for a lot of ethnic programming, using MPEG-2 receivers. Or you could enjoy the 101 slot, which could provide the same signal now provided by the 18-inch RCA DBS antenna. Those inclined to religious programming might put a Ku-band LNBF in the same location for the 3ABN 7th Day Adventist channel. Whatever you do in the center of the arc, you can very likely get a DBS bird 20 degrees either direction without any problem; more if you are very careful. 120 plus channels of digital audio await those listening to both NIMIQ 1 and ECHOSTAR at 119. If your tastes are more extreme, we recommend the "battleship" reinforced 90 cm antenna from Paraclipse, which will give a little more range & stability.

MULTIPLE FEED ANTENNAS: Rediscovering An Old Idea

Some logical limitations and facts you should know before attempting one of these antennas: We have found it entirely possible to receive DBS satellites 25 degrees off boresight on a 90 cm dish. Due to the average power on current Ku-band satellites (11.7 to 12.2 GHz) being anywhere from four to eight dB less than that of most DBS satellites, don't expect similar spillover results. We recommend limiting the search for domestic Ku-band signals to be within 15 degrees of the center pointing azimuth of the antenna. The weakest Ku-band satellite should be as close as possible to antenna boresight, which might give a few more degrees' tolerance from center on the remaining satellites. Ku-band satellites are linearly polarized (horizontal and vertical). This requires precise adjustment of the polarization setting on LNBFs (clockwise or CCW). Circular LNBFs used on DBS satellites are quite forgiving in this respect, and can be turned just about anywhere without worrying about loss of signal. Just avoid pointing the F-connector upwards without any waterproofing measures. DBS satellites are typically 9 degrees apart, which also makes for easier setup than Ku-band types. On a 90 cm antenna, you can generally space Ku-band LNBFs 4 degrees apart. Since Ku-band signals can be found as close as two degrees apart, at least two, if not three reflectors would be advised should you want fulltime access to all available Ku-band satellites. Alternate spacing on two antennas (85-89-93-97-101- 105 on one dish, 87-91-95-99-103-107 on the other)... possibly another dish for the extreme west or east end of the arc. Larger dishes allow for more distance between LNBFs, and increased concentration of signal on the satellites being viewed. But you may be lined up with the outer edge of a 1.2 meter antenna before you get 20 degrees from center. Some experimenting may be required to decide on the proper number of LNBFs versus signal strength on Ku-band linear, for your given situation. Our recommendation is to start with a 90 cm type, and see what works for you. It has the advantage of being UPS shippable, thus avoiding the larger costs found when making single small shipments via motor freight, which is the only way to send 1.2 and 1.5 meter antennas. GLOBAL COMMUNICATIONS S-9141 State Highway 23 Plain, Wisconsin 53577 Telephone (608) 546-2523 Email globalcm@mhtc.net		Two types of mounting brackets are available for the 90 cm type of antenna. 1) Paraclipse 90 cm with full range of available satellites. 2) ITI 90 cm or Pansat 95 cm, with limited range free-standing mounting bracket The Paraclipse-90 with full range multifeed bracket will be sold at the same price as the ITI limited-range bracket. Materials costs are similar, thus the same price. Those wanting a simple system parked on one main satellite possibly Telstar 5 at 97 West, or either the DBS satellites or GE-4 Ku-band at 101 West, a computer system for DirecPC at 103 West, or even a Star Choice system at 107.3 West. Plus a couple of DBS LNBFs for reception of satellites such as NIMIQ at 91 West or ECHOSTAR at 119 West. There are many possibilities offering a mix of subscription DBS reception as well as MPEG-2 free-to-air reception that might want a simple yet strong installation through use of the short bar matched to the ITI or Pansat dish. (larger Pansat dish costing a little more than the ITI) The bar itself attaches directly to two connections using the same bracket holes as the LNBF. The Paraclipse design uses a special LNBF bracket at the center, and everything balances on it through use of some offset rods. Flexible at first, strength is added by connecting extensions onto the multifeed bar and securing to the side of the dish, giving a it a super structure effect when the results of all components are added together. It takes a bit more patience to get it installed perfectly, but as with all good things, the extra effort can result in perfection. One added factor about this design is that the multifeed bar positions below all LNBFs, eliminating the possibility of the bar itself getting in the way due to its matching the same elevation angle as some satellite in the arc. An independent measure of both the ITI and Para- clipse 90 cm antennas showed roughly 0.5 dB more signal on the Paraclipse. This extra margin can be useful on weaker satellites. The measured gain of the ITI 90 and Pansat 95 was virtually identical. Where the Pansat might prove useful is in its T-mount design, which does not need a separate pole or wall bracket to be installed for the mounting of the antenna. This is most useful in flat roof installations. We're trying to give you some options. More information will be added to this section as we develop additional products.