Do's & Don’ts of Dish antennas, what they don't tell you! By Grandpooba - (Updated 20

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Do's & Don’ts of Dish antennas,

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what they don't tell you! By Grandpooba - (Updated 2008-07-24)

Background:
Television entertainment satellites are in a geo-synchronous earth orbit (moving at the same speed and direction as the earth is turning) above the Equator, so the satellites appear stationary in the sky to us here on earth. Dish antennas are commonly used in satellite reception. Their function is to receive the highly directional radio waves, concentrate and focus then into the LNB (Low Noise Block converter). The LNB's job is to sort, amplify and condition the concentrated signal to a stronger level for transmittion down the cable to our receiver.
In FTA "surplus" major providers logo dishes are very common. One on the most popular low cost surplus dishes is the 18 to 24 inch round/oval. Your distance from the Equator and "foot print" of the satellite determines the size of the dish required for your installation. The greater the distance the larger dish is required. This 18 to 24 inch round/oval work well for S.Canada and continental USA reception of provider’s circular satellites.


Different types of fixed dishes;
The dishes can be divided in to two basic groups, single LNB dish and multi LNB dish.
The single LNB dish is a round or vertical oval dish that is non-skewing (non-tilting).
The multi LNB dish is an oval dish with more than one LNB and it is a SKEWING (tilting) dish.

Skewing:
This is the dish being able to rotate on its center axis (similar to the steering wheel of a car) to track multi-satellites. If you could see the satellites in the sky, they would appear in an arch, like a rainbow. Skewing is necessary to tilt (align) the LNB's to match the satellites in the rainbow arch. If the satellites are at the top of the arch, not much skew (tilt) is required. However if you follow the arch down with the dish you would have to rotate the LNB or dish to keep the 2 noses of the LNB aligned with the arch and satellites. To determine the amount of skew for YOUR location you must use a multi-satellite aiming site such as Satellite look-angle calculator.

"Poormans" dual (LNB) dish:
These are 18 to 24 inch non-skewing dishes that have been user modified to add a second LNB for reception of a second bird. They work well with certain restrictions, as follows, the skew for your location and satellite selection should not exceed +/- 5 degrees (Skew range between 85 to 95 degrees, a non skewing dish is considered to be at 90 degrees), and the positional span of the two satellites should be less than 10 degrees, it will usually work for 119/110 (119 - 110, span = 9 degrees) or 91/82 ( 91 - 82, span = 9 Degrees). The above angle restrictions are recommended as if you exceed them, the position that you would have to mount the second LNB at would not get a good reflective signal and you will loose signal strength. Note: There are after market LNB "Holders" sold, that claim larger spans, but they don't tell you about the signal loss, and that they should be used on a skewing dish, use at your own risk.

Signal to LNB reversing;
If you are in the northern hemisphere (Canada & USA) and look to the southern sky, the easterly satellites have lower positional numbers, and the west satellites have higher positional numbers (110 would be left of 119). However when working with a multi-LNB dish, standing behind the dish with the post in your belly, looking at the white nose of the LNB, the "most" right LNB will be the most EAST satellite and lower positional number, and the most left LNB will be the most WEST and higher positional number. The signal beams reflect and cross (reverse) on the dish. This can be very confusing, as I have seen many make the mistake of using the incorrect right LNB on the highest satellite or left on the lowest, this will work for ONE satellite, and you can spend many hours trying to find the other satellite on 2 LNB dishes. A simple test is from behind the dish (pole in your belly), reach UNDER the dish and put your 2 fingers over the front of one of the white hockey puck noses of the LNB's and watch the receiver signal. The signal will drop if you are covering the LNB that the receiver is using.

"Y" and Multi-LNB adaptors:
These adaptors are available at satellite stores and secondary markets and are designed to be used with skewing dishes. The further off center that the LNB is away from the focal point (center) of the dish the greater the signal loss. You can use these with non-skewing dishes IF there is no slew required . You to use MUST check the lentgh of the LNB to dish center so the measured distance from the nose of the LNB to the center of the dish remains the same as original. These adaptors need to be researched prior to purchase to see if they will work in YOUR location for the desired satellites, as you will loose signal strength as the LNB aim gets moved from center (focal point) of dish, the original LNB gets the reflected signal from the whole diameter of the dish. When your adaptor aims the LNBs off center of the dish, it will miss a "slice" of the dish and reduce the reflected signal into the LNB. These are not recommended, unless you are in a very strong signal area. If in a average signal area, they will require constant re-adjustment if they work at all. I recommend a "Factory" stock dish, as the dish engineers/designers, designed it for minimum maintenance and maximum stability.

Dish mounting:
Most 18 to 24 inch dishes come with a "universal" mounting arm, for mounting to dwellings etc. For post mounting, a standard 1 5/8 inch chain link fence post works well, is low cost, comes in various lengths (5 to 11 ft.) and is commonly available at fencing or hardware stores. Any dish installation, (universal or post mount) should be solid and most important, LEVEL on all planes, this means put a bubble (AKA Spirit) level on all 4 sides of the mounting post, the bubble MUST be in the middle, as the dish will rotate on this post, and you will be trying to find a satellite the size of a car at 22,000 mile away.

22-degree signal offset:
This is very important to you if you are surveying a prospective dish site. The dishes are manufactured with a 22-degree signal offset. This means if you put the face of the dish vertical (90 degrees to the horizon), the signal would be coming in at 22 degrees above the horizon. I have seen dishes on a dwellings, mounted on the lower edge of a roof and the dish appears to be aimed into the roof but because of the 22 deg offset, was shooting over the peak of the roof. A simple way to see if you can get a clear signal is to use a "inclinometer" (AKA "Angle Locator"), a flashlight or a laser pointer, look up the elevation and azimuth on a satellite aiming site. Find the Azimuth using a compass, add (or subtract, depends on the angle finders scale) the 22 degrees to the elevation reading. Hold the flashlight or a laser pointer on the measuring side of the "inclinometer". Sweep the Azimuth while maintaining the angle to see if it hits ANY obstructions.

Elevation setting on the dish:
I have found that the "elevation" scale that is stamped into the dish is not always accurate. My experience is that +/- 5 degrees is not uncommon. So when you get the elevation setting from a satellite aiming site on a new install, start at the specified elevation and S-L-O-W-L-Y sweep in the satellites direction, can't find, change the elevation 2 degrees and re-sweep, repeat until found.
You can also accurately set the elevation on the dish by the following procedure, look up the elevation angle for your location on a satellite-aiming site (For example we will use 50 degrees). Take the 50 degrees and subtract the 22 degrees offset and you get 28 degrees. Put a straight edge from the center of the LNB arm to the center of the top of the dish edge, with the straight edge touching only the dish edge. Using an "inclinometer" (AKA "Angle Locator") set the angle for 28 degrees (some inclinometers have a indicating scale that you may have to take 90 degrees and subtract the 28 degrees and set for 62 degrees).


Toroidial Dishes:
These are not provider-supplied dishes, but are specialized dual reflector dishes that have a larger satellite positional span. They work well but are difficult to setup and require special "Reversed" LNB's for Circular reception. Not recommended for newbie’s.

Motorized Dishes;
These are usually larger dishes that are 30 inch or larger (for linear signal reception and/or weak circular reception) and have a positioning motor that is controlled by the receiver. When properly setup, the motorized dish with a linear and a circular LNB you can receive any satellite it can see and the receiver can decode. There are special single LNB’s that can receive both Circular and linear signals such as the Invacom QL series LNB. The motorized dish also has its drawbacks. They are complex to install and properly setup. They are slow when channel surfing and the motor has to switch satellites, (it takes about 10 seconds to change from 119 to 110) and to run more than 1 receiver is difficult as both receivers must be watching channels on the same satellite.

Recommendations for Newbie’s;
Circular satellites - Start with a single LNB dish, or for future expansion, a dual skewing LNB dish (a "Dish 500 is recommended) with 2 each SINGLE Legacy LNB's with dual output. To start, use one LNB connected directly to the receiver without switches. Get 1 satellite going, and then expand to the second, ALWAYS hook direct the Receiver to LNB (no switch), aim and peak, once all dishes are OK, then add the switch.
Linear satellites, a single 30 to 32 inch dish with a single linear LNB.

Diseqc Switch CAUTION:
Diseqc switches, MUST be treated with kid gloves! They are physically rugged but electrically delicate. These switches are solid state, and can be Easley damaged. The most common way the switch is damaged is to make or break ANY connected dish cable connection with the receiver PLUGED in to power. The receiver puts power out of its LNB connection (and through the switch to the LNB), even if the receiver is turned off by the I/R remote or front power button! YOU MUST REMOVE POWER by unplugging or using the REAR power switch. I know it is a pain in the A** when you are on the roof with your satellite finder, have to peak the dish, and have to turn the power on/off to install/remove the satellite finder.
 
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