Talk:Big Dish Satellite T.V. Hobbyist's Guide

ACRadio's Choosing A C-Band Dish (Written November 2, 2005)

Many people are now looking for used C band equipment after discovering the amount of DVB channels available on C band. During the big dish boom of the 1980's there were jillions of BUD manufacturers...some with quality products and some with trash. Below is a guideline on what to look for in a BUD, and what to look out for.

There has always been the discussion of mesh vs. glass vs. perforated. Mesh dishes are lighter and much easier on an actuator, but can be prone to structural damage if you live near a wooded area. Limbs and brush can be blown around by storms and make dents or poke holes in the mesh, not to mention possible hail damage. Some of the earlier mesh dishes had larger holes which cut down a bit on their efficiency, especially if you require KU reception. Don't listen to the hype about a mesh dish not being as prone to wind damage. After the wind gets past damaging stage (50+ mph) the dish cannot pass enough air through the mesh to keep the pressure behind the dish equal to the pressure in front, so it acts just like a solid dish, and the panels will blow out. Boom Boom, out go the lights....

Fiberglass solid dishes are more resistant to contact damage, and they are more true to the parabolic curve, as the fiberglass can be shaped to a much truer shape than mesh panels. The downside though is the fact that glass dishes are MUCH heavier, and after exposure to some seasons of weather the panels can warp in varying degrees. They are much harder on an actuator, and require a much more substantial mounting foundation. Absolutely never get a one piece fiberglass dish. The bottom line is...they WILL warp. I don't recall seeing a one piece that was more than 2 years old that wasn't warped. On a multiple piece dish (3 or more pie shaped pieces) you can tolerate a very small amount of warpage because you can do something about it.

Perf dishes carry some of the same traits as glass dishes, in that they are heavy. Some were stamped steel, while others were aluminum. Their signature is the perfectly round "perforations" in the reflector. Some were one piece and while not quite as easy to warp, when they DO warp there is nothing that can be done. They also aren’t as resistant to contact damage. A perf dish will hold its shape better over time than fiberglass.

The real gold nugget of dishes is the spun aluminum. Even though they are one piece they have a stout rolled edge and aren’t as prone to warp unless they were dropped. Their efficiency is superb. Anytime you have an opportunity to snag one of these treasures you better grab it.

I prefer medium or shallow dishes over deep dishes because of their efficiency. A deep dish is harder to illuminate. They were popular in the 1980's because the feedhorn was further down toward the center of the dish, and it helped to shield it from the terrestrial interference from Ma Bell.

There are two basic styles of feed supports used on BUDS…monopod and “milk stool”. The milk stool feed can be a 3 legged (tripod) or 4 legged (quad pod), while the monopod has a single arm coming out of the center of the dish. The milk stool feed is much more desirable than the monopod for several reasons. The feed must be perfectly centered for proper illumination, and as well, the feed opening needs to face dead center of the dish. It’s sometimes hard to bend or force a monopod to hold the feed in the proper position. A guy wire kit is essential for a monopod feed, not only to move the feed into the correct position, but to keep the feed from bouncing in the wind because of the weight of all the electronics on the end of the arm. Some monopod supports were substantial enough to prevent this, but are rare. The milk stool supports were usually machined to put the feed in the correct position in front of the dish. But if slight adjustments are needed, it’s easy to use some shims such as small washers to make the geometry correct. There is a third kind of feed design, called a “cassegrain” feed, which a second reflector is held in front of the dish, and the signal is reflected down a tube to the rear of the dish, where the feed and amplifier are located. This kind of feed structure is very rare.

In the early days of satellite TV, we weren’t interested in much of anything east of 70 degrees west. But today there are many satellites of interest beyond that boundary. Horizon to Horizon mounts are desirable to have, but are expensive. Polar mounts with linear actuators are the norm. Some people will use 2 different dishes, one for the western sky and one for the eastern sky, and mount the motor on opposite sides. There are 3 angles to adjust on a polar mount. Azimuth and elevation are very well known, but there is a third angle called “declination”, or “offset” angle. The offset where I live is 5.8 degrees, and will be different at different latitudes. Some mounts just had multiple holes on the top swivel bolt, so you had 3 offset choices…2.5, 5, and 7.5 degrees. You just picked the hole closest to your calculated offset angle. Better dishes had a fine adjustment of the offset angle, again located at the top swivel bolt.

I recommend a complete disassembly of a used dish before putting it on the pole, and here are some basic guidelines. If you can afford it, replace the hardware with stainless steel. Grease all moving parts of the mount. If you must repaint, use enamel, and never use a gloss or metallic based paint on the dish surface. Disassemble the reflector, and swap a set of opposite panels so that no joint that was previously mated will be mated again. On a 4 piece dish, swap 2 with 4, and on an 8 piece swap 2 with 6 and 4 with 8. This will help curb any rim warpage. Always reassemble the panels on a flat surface such as a paved driveway or parking lot. Put ALL reflector bolts in finger tight. Tighten the bolts in sequence, beginning with the rim bolts and work your way around in a spiral and finish with the centermost bolts. Avoid letting the dish stand on its rim, as this can distort the shape you worked so hard to maintain. You can use a hammer and block of wood to gently tap dings out of mesh panels. Know the manufacturers stated focal point of your dish, and measure to assure that the focal point is 1/8 - 1/4 inch inside of the throat of the feedhorn. Make sure the feedhorn is centered in the dish and pointing at the center plate.

I am going to voice an opinion here so just take this as an editorial comment. Avoid using a BUD for KU reception unless absolutely necessary. BUDs are just not designed for KU reception...they are a compromise. Even with tight mesh they are not efficient. Offset dishes work much better for KU reception, as they usually use a reflecting surface similar to screen door wire. The only exception to this is a spun aluminum dish such as a Birdview or DH, or a stamped steel dish such as a Patriot. These are great performers for KU, as there is no loss of signal through any mesh holes. A Patriot is not likely to be found in someones back yard as it's used mainly in commercial installations. A specific model of Channel Master fiberglass dish that uses the same reflector material as their commercial offset dishes works well also, and is what I am using because of their availability in my area.

I hope this will help people to choose wisely among the thousands of dishes available from people who desire to just get the thing out of their yard. There are some gems out there, as well as some trash. A little information will make your C band dish selection pay dividends in performance both now and in the future. __________________ 19 operational dishes