Satman Canada's Report on Small Elliptical Dishes

Satman gets calls every day about elliptical dishes. It usually from people who have purchased these units at big box stores. These big box stores are the same ones that are or ( maybe were ) selling you clones . Now they are selling another product that is a counterfeit-- the elliptical dish. This discussion shows in text book terms why the elliptical dishes sold in big box stores represent an absolute waste of money.

Multiple Feed Dishes

In real world COMMERCIAL applications especially in a cable company environment multiple feed dishes make sense. Prime cost considerations are dish size used , available space , and channels to be carried . Global CKND in Winnipeg uses several dishes to pick up program feeds but they are running out of room and sit on a valuable commercial location .

CKND Winnipeg VHF channel 12 .The late Izzy Asper built his Global empire from this flagship location.

All of these commercial applications work because BIG dishes are used

Most people reading this article are hobbyists. In that environment a .9m (36 inch) dish can be used to receive multiple feeds. Most people in Winnipeg center LNB's on T5 and pick up feeds on either side . It is a concept that works well because a .9m dish provides adequate signal plus the .9 meter width gives one enough span to properly place 3 or 4 LNB's. In the Winnipeg market multiple feed dishes are not cost effective when one considers materials costs and professional installation .

Typical costs

.9m dish $99.00 LN B's.... $29 each (assume 3 used) $87 ....Digiwave Bar Kit $40.00...Professional install 3 hours $125...Total $350

(don't worry folks just like in those commercials Satman takes VISA)

Such a project will produce excellent results however when one looks at pure costs other alternatives exist . Use 3 18 inch Dishes at $50 each plus $100 install Total $250 ...or one Dish 500 one 18 inch dish cost $185 install cost $125 Total $310.

As a result of these costs the Elliptical dish at a basic cost of about $150 looks attractive. Now Satman will tell you why you are wasting your money on poorly engineered counterfeit Elliptical dishes.

Small Elliptical Applications

Small Ellipticals abound in the real world and they do WORK. Why do they work ?? Because DBS companies such as DIRECTv and DISHNET have a staff of professional engineers to correctly design products for applications needed to deliver specific solutions. Usually such designs incorporate a dish to receieve the providers satellites using specially constructed LNB's and switching systems . The transmitted information is received and processed by receivers issued by these providers for that specific purpose. They are a perfect match.

As the following illustrations show each dish is designed for a specific satellites and a specific switching function.

Gain Master 35 x 26

Phase II Plus 18 x 22

The Gain Master measures 35 x 26 and offers 65% more gain than the Phase II Plus .

Clone Counterfeits

Here is an example of a typical counterfiets of the Phase II Plus

110/119

This baby is claimed to do 110/119 82/91

Does it really work?? No... Here's why...

Diffraction, or Why Small Dishes Don't Work Well by Paul Wade author of The W1GHZ Online Microwave Antenna Book

The design of multiple reflector antennas is derived from telescopes and other optical
systems, so we use the quasi-optical design techniques of Geometric Optics. For these
approximations to be valid, three basic assumptions must be satisfied:
1. Wavelength is much smaller than any physical dimensions, so that we may use the
approximation of zero wavelength.
2. Waves travel in straight lines, called rays.
3. Reflection from flat surfaces follows the Law of Reflection: the angle of incidence = the
angle of reflection.

4. Refraction follows Snell's law shown in (a dielectric is required for refraction).

A good pictorial description of refraction is available on the web by Prof. Joseph F.Alward of the University of the Pacific.
Many of the small dishes used by hams stretch the limits of these assumptions; performance
may be compromised, but still usable. A typical dish might be only ten wavelengths in
diameter or even smaller. Any usable feed has an effective electrical size larger than half awavelength, so the feed is much larger than a point source. According to Huygen's Principle, each point on a propagating wavefront can be considered as a secondary source
radiating a spherical wave. The propagating wavefront could be the aperture of a feedhorn.
Figure 10 shows a 10λ diameter dish with rays emanating from points across the aperture
rather than a single point. The result is that the rays from the parabolic reflector are no
longer parallel, but rather spread out into a diverging beam. Note that rays reflecting near the
center of the parabola diverge more than rays farther from the center; from this, we might
infer that that smaller dishes would have even broader beams.

Figure 11 shows smaller dishes, 2.5λ and 5λ in diameter; as we expect, the beam becomes broader as the antenna gets
smaller.

The diagrams and formulas show that the smaller the dish the greater the diffusion . That is to say that small dish reflections miss their target -the LNB - more often .In practical terms what this means is a 24" dish feeding multiple-3-lnbs diffues the signals to the point that they are weak and low in strength and quality.

If you want to really learn about antennas read the Paul Wade publications by Googeling Paul Wade W1GHZ . He is a prolific writer on this subject and is a recognized expert. His articles appear regularly in QST Amateur Radio magazine.

Solving the Elliptical Dish Problem

DBS Providers do offer paying customers well engineered solutions . The BEST FTA solution is a .9m dish with a motor and a QPH-031 LNB you get accurate pointing and maximum reception on all satellites. The second best solution is using 2 dishes usually a dish sized correctly to pick 2 adjacent satellites and a second dish properly sized to pick up a third satellite.

Remember big box computer stores are only selling products at a price . They are in the computer business and use the satellites as a traffic builder.Our ethical commitment our customers is to test all products publish honest reports about there products .Sell products that are high end quality.

Only satmancanada.com provides you with EXPERT ADVISE...HONEST ANSWERS...and LOW PRICES . Satellites is what we do BEST.. it is our ONLY Business.