Dish Mounts

Most people look at the front of the dish; I find the back of the dish much more interesting to see how it is mounted and rotated.

Most BUDs have a polar mount, meaning that one axis is aimed up towards the North Pole in the Northern Hemisphere. Then the dish is swung either mechanically or electrically through an arc to point to signals from several different satellites parked along the Clarke belt about 22,000 above the equator. This arc is known as the "Right Ascension" axis in Astronomy terms. The dish mount is usually placed on top of a tall steel tube firmly anchored in the ground. Alignment to the North pole is usually achieved by rotating then locking a top cap tube to the ground tube, along with moving an altitude turnbuckle so that the Right Ascension axis will track all of the satellites in the Clarke Belt. Because the satellites are a finite (22,000 miles) distance up instead of ~ infinite like the stars, a slight offset of about 6 degrees (Colorado) is applied to the Right Ascension arc.

Most polar mounted BUDs use a linear arm, called a Houston tracker arm, to swing the dish through the Clarke Belt arc to pick up several different satellites. My Janeil dish used a fiber gear mated to a worm drive. Incremental pulses are sent to a control unit in the house to keep track of where the dish is pointed. A local satellite shop gave me a perforated 5' dish that was chain driven.

 

A few BUDs are not polar mounted because they are used in fixed positions. These are frequently found at either local cable TV headquarters or sports bars. These will have an ALTAZ (Altitude - Azimuth) mount which is mechanically adjusted to a certain satellite on the Clarke Belt, then locked in place. The ALTAZ BUD pictured at the right uses a simple square framework for dish support and elevation rotation. The Adjusting arm sytem looks weak and would be stronger beneath the mount than on top of it.

Conversion of a BUD to Amateur Applications

A short trip around most neighborhoods will generally find an unused 5' to 16' BUD (Big Ugly Dish). I had a 10' Janeil perforated dish, mostly unused, mounted in my backyard. Recently I found a14' fiberglass BUD pictured at the right with all the driving and receiving electronics advertised in the Denver newspaper as "free - take it down and away". 4 hours later it was disassembled and in my backyard. Another source is a local satellite dish installation & repair facility. The market for BUDs is dead, and people want to get rid of their BUD when they decide to subscribe to satellite service using a "Hubcap" dish.

An article in July, 2003 QST described how to use a 10' BUD without converting the mount from polar to altaz. I would not recommend doing this as the satellite has significant departures from the Clarke belt, and no software satellite tracking program will give the bearings required. The off axis gain will also be poorer.

Converting a BUD to amateur use simply entails converting the mount to a motor driven ALTAZ mount and adding a method of reading out the direction the dish is pointed. If the BUD already has an ALTAZ mount, then only the motor drive(s) and readouts are needed.       

But most likely the mount you have or obtain will be a polar mount with Clarke Belt offset. (Notice in the pictures that one pivot is 2 1/4" from the dish and the other pivot is 3 1/2" from the dish.) In this case, you will have two choices:

1. Rotate the polar head 90 degrees and flatten the elevation so that the Right Ascension Axis becomes the elevation axis. You will also have to compensate for that Clarke Belt offset or your azimuth settings will change slightly with any elevation change.

2. Make a a new elevation axis bearing for your dish which is perpendicular to the azimuth axis. I recently saw this dish and mount at a Cable TV business in Green River, Utah. A simple horizontal axle as shown on this Altaz Cable TV dish would work well for amateur use.

The plate holding the elevation arm was welded to the top of the top cap, but it could be U bolted to the dish side of the top cap which would provide more dish to post clearance for the tracker arm. The top cap tube is about 5' long, making it easy to mount a motor at the bottom without clearance problems. Replace the mechanical elevation screw with a tracker arm and the job is done!

 

Whether you want 1 or 2 axis control, the top cap tube that holds the mount and rests over the ground mount tube must be modified so that it will turn in azimuth under motor control. Though this seems like the easy part, actually there are a number of "gotchas" that will probably make it the toughest part of the operation. My Janeil dish was installed and the top cap locked in 1986. By 2001, it was rusted SOLID! After loosening the locking bolts, two 1 1/2 ton car jacks pushing up on either side of the bottom of the top cap couldn't budge it. I drilled some holes and soaked the top cap to mounting post area in "liquid wrench" oil for 4 days. It still wouldn't move. Finally I connected a 8' long trailer tongue I beam to the top cap ears and hooked the end of the I beam to my truck. That got it loose. A local satellite dish shop told me that they loosen rusted dishes with a torch.

Working on the mount is easier if the dish is taken off. My 10' dish had a zillion bolts holding the perforated panels together, so I rigged up a tower installing gin pole alongside the ground pole and after removing the elevation bolt and turnbuckle, lifted the dish and mount in 1 piece and set it on the ground. All by myself! Lowell White of Texas wrote me, "Pulling the dish temporarily to place the open sprocket on the support is not a big deal. Two guys and 5 minutes..." I found that the top cap rust problem was made worse by an internal seam. I ground away this internal seam with my Dremel tool so that the top cap would turn totally free on top of the ground tube.

 

Chain Driven Azimuth System

Several years ago, I met a fellow who designed an optical telescope mount using a triple chain drive on the Right Ascension axis. The chain driven axis has several advantages, such as flexibility, strength, low cost, and availability. Chain drives are used on bicycles, GoCarts, motorcycles, and machinery. Chain drives will not slip until they break. The chain drive systems use various sized sprockets and chain to achieve different drive ratios. Stand chain is rated in working load and Tensile strength.

Standard ANSI roller chain is available in many sizes. #35 and smaller chains often do not have rollers and are not recommended. Obviously, a large dish requires a chain with a larger working load and tensile strength. Sprockets come in many configurations such as sprockets with hubs and hubless plain bore sprockets. Sprockets are usually one piece, but occasionally 2 piece sprockets are made, such as GoCart sprockets. A 2 piece sprocket could be mounted around the dish mount's top cap without removing the mount from the post, but it is better to remove the dish, add a "lazy Susan", and use a one piece sprocket.

Smaller TVRO dishes, such as 5' and 7 1/2' dishes can use #40 chain which has a tensile (breaking) strength of 4,300 lbs. Larger dishes, such as 10' to 14' dishes, should use a larger chain and sprocket system such as a #50 (7,200 lbs) or #60 (10,000 lbs). Double and triple strand chains and sprockets are also made but are quite expensive.

I recently visited Surplus Center in Lincoln, Nebraska (800-488-3407). This is an excellent source of chain, small sprockets, gear motors, and flange bearings at reasonable prices. I also visited McMaster-Carr in Chicago, Illinois, a very large supply house, but was stone walled by the front receptionist, 3rd class. Their prices are usually very high as well. Use them only as a last resort. Local motorcycle and GoCart stores are your best local source. Motorcycle parts are expensive but built to take abuse.

I obtained and attached a 10" diameter 48 tooth replacement motorcycle sprocket and a matching 12 tooth drive sprocket + a matching "520" chain from a Denver motorcycle supply house. . I mounted the 10" sprocket on the bottom of the top cap assembly, using some 2" square aluminum tubing as a support. The chain only needs to be about 36" long.

 

Since the weight of the dish and mount would be significant, I built a "lazy Susan" horizontal bearing that would support the weight of the dish and mount on top of the ground tube, yet allow the dish & mount to freely move around in azimuth.                                                                         

  After liberally coating the top of the ground tube with a low temperature grease, I placed the lazy Susan on top of the ground tube, and slipped the top cap over the ground tube. Now the top cap & 48 tooth sprocket assembly will turn easily. The gin pole lifted the dish and mount back on top of the ground tube and the Right Ascension axis polar angle was adjusted to be flat so that this axis would function as an Elevation axis. Check for how much clearance you will have, which determines how far away you can mount the 12 tooth drive sprocket.

The 12 tooth drive sprocket was mounted on the mounting tube below where the bottom of the top cap will be. Oversize mounting holes in the holding plate for the 12 tooth sprocket permit adjusting it so that the chain can be put on and tightened. Align the sprockets for zero runout and fit the chain around the sprockets. Attach the master link, and pull the chain VERY tight so there is no slop.

You will find that there is very little extra room at the mount area for a drive motor unless the elevation axis is significantly offset, or the top cap is quite long. By making a long shaft (I used 3/4" threaded rod) for the 12 tooth sprocket and mounting the motor below, there is plenty of room for the motor, because the dish, even when at 0 degrees elevation, will curve away from the mounting tube. I used an 8" pulley with a 5/8" hole to a 2" pulley on a 3RPM 24VDC reversible gear motor. Overall I have a 16:1 step-down for my dish, which will now turn at better than 1/4 RPM, a bit slow. By increasing voltage it runs faster, of course. A 5 to 10 RPM gear motor would be ideal for tracking full sky satellites, but the1/4 RPM dish azimuth speed is perfect for equator orbiting satellites like AO-40.

Attach your tracker arm so that the dish will move in elevation between 0 and 90 degrees+ if you wish to have 2 axis movement. A satellite will always pass through 0 degrees elevation twice each pass, and between 60 to 90 degrees in elevataion either rarely or never! The VLA 82' dishes are parked at 90 degrees elevation for minimum wind loading. 0 degrees elevation would be better if you are expecting snow, or rain with a solid dish and no center hole! AO-40 never moves very far North, so most of the time in the USA, the dish will be pointing from East through South to West, and from about 0 degrees elevation to about maybe 60 degrees, depending on how far from the equator you live (The closer you are to the equator, the higher the satellite can appear.) The biggest elevation problem you will have with these converted polar mounts is that they will probably have trouble reaching 0 degrees elevation. I had to cut away some of the mount with a sabre saw to provide axis clearance at the lower elevations. My dish will now reach down to about 4 degrees elevation. The majority of satellite access time is spent at the lower elevation angles between 5 and 30 degrees elevation.

Gary, W6RYO, has a BUD webpage showing details of his AO-40 12' dish and feed that you should check out. Gary has some really interesting tales to tell about his experiences!

Tracking objects anywhere in the sky presents a special problem. Ideally the dish should move 180 degrees in elevation and 360 degrees in azimuth. Most, like your dish, won't. A Houston tracker arm dish definitely won't, and my Janeil gear driven elevation axis would, except a stiff horizontal strengthening arm on the high side limits movement to about 140 degrees. What you definitely want to avoid is a 180 degree azimuth flip as the pointing passes through the zenith (overhead)! This can be achieved by allowing the azimuth to move through 450 degrees (1 1/4 turn) and the elevation through 90 degrees. The satellite tracking program NOVA from Northern Lights will drive a system set up like this.

Be sure to put 4 limit switches on your dish. A limiting Microswitch with a properly polarized 6 amp diode across each limit switch will stop the motor from jamming and stripping the gears, and, when voltage is reversed, will back up.

Read the full story behind my 14' Dish on an Elevated Clothesline Mount.

Recent Dish Acquisitions

I was given three more dishes.. The first dish was a 7 1/2' Echostar. This dish was unique because the mesh dish and its frame were made of light weight aluminum. The dish was removed from the owner's residence in about an hour. The 3 1/2" x 5' high steel post was removed by grinding it off at the top of the concrete pad with a power handgrinder in about 10 minutes.The dish was made in 4 sections. I disassembled the dish into two sections, and loaded the whole dish system into my Toyota 4Runner for the trip home.

    I decided to make this dish portable. I had a heavy steel triangular polar mount base discarded by a satellite shop, so I welded the 3 1/2" x 5' pipe to a plate that could be bolted to the triangular base. The plan is to fit everything into my 4Runner. The triangular base goes in first, followed by the 3 1/2" x 5' post. Next goes the mount, then the tracker arm. The 4 dish sections are placed on top of the mount, and finally the feed section and positioner are loaded. Everything fits inside the 4Runner and off I go. Reassembly should take less than 15minutes..

The mount was very easy to convert from a Clarke belt offset polar mount to a perfect elevation and azimuth mount. The Clarke belt offset was nulled out by using a longer standoff bolt on one side of the polar axis. Then the pivot axis was reduced to zero and the head turned 90 degrees, ready for the attachement of a sprocket, chain, and gear motor for Azimuth control. The Houston tracker arm will be used for the Elevation control.

Unlike the 10' Janeil, the 7 1/2' Echostar mount goes all the way to 0 degrees elevation without any frame cutting. The third dish I was given is another 7 1/2' dish from Kaul-Tronics, almost identical to the Echostar dish, both dishes obviously from the same manufacturer.

The second dish was owned by W0GLG down the street from me. He wanted to use it as a solar concentrator for heating domestic water. The dish itself was a military surplus heavy aluminum 6' dish which he had faced with shiney contact paper. At the focal point he placed a small radiator through which water from a 55 gallon drum would be circulated. Unfortunately it was too good at collecting heat, because what he got was 55 gallons of steam!

Tom had a special altaz mount built for turning the dish into the sun. It has an elevation jackscrew, and an azimuth worm gear. By adding a pair of 20 RPM gearmotors, it's a natural for use as a small dish & mount that can be moved around, with some difficulty.

Making a Plumber's Delight Portable Mount

If your wife or neighbor is given to complaining about that ugly little dish that she has to look at from the kitchen window, try this cheap little portable mount that you can easily move out into position when AO-40 comes up at night. Apartment dwellers facing South could put it out on the porch to work the world and take it inside when done, nobody the wiser .It also works great for mobile operation because it can be taken apart or assembled in a few minutes and fits easily into the trunk of a car. Instead of listening to your brother-in-law drone on about the football game, set it up and work friends (or me) on AO-40! The weight with rotators is 42 lbs. Maybe another 10 lbs for the dish and 11 element beam. I use it it test out my new dish controller and various dish feeds that I design..

The mount uses 28 pieces of 1 1/2" Schedule 40 PVC pipe, 25 fittings of 1 1/2" PVC, a 2" metal pipe flange, 2 old TV rotators, 3 plates, a mast & boom and some misc attachment hardware. You should be able to get everything at the local hardware store except the plates and rotators. If it costs you over $100, you are not a good ham shopper.

Shopping list (all 1 1/2" Schedule 40) :        Two 10' lengths of pipe.   One Cross X.    Eight Tees.    Four  45 degree elbows.     Eight 22 degree elbows      Four end caps.       Also get a small can of PVC cement,   a small can of Acetone,    2" black pipe Flange~4" in diameter,    4" long piece of 2" PVC pipe for insulated thrust bearing,    Ten 2" U bolts with nuts,       Eight 1/4-20 bolts 2 1/2" long with wing nuts,     and some 1/4" plate aluminum for mounting rotators and thrust flange. 

Start by cutting the 10' lengths into the needed 28 sections. Cut the biggest pieces first. I use a radial arm saw, and after cutting the bigger pieces out, I finish cut all similar pieces to exactly the same size. When my wife first saw this mount , she said, "Oh, you're making R2D2!"

Cut four 24" pieces (legs), four 17" pieces (bottom cross pieces), two 10" pieces (top), six 3" pieces(top & legs below the cross pieces), and twelve 1 1/2" pieces which are used to join the fittings.   The picture at the left shows what you should wind up with. The bottom cross pieces could be made 20" long instead of 17" for greater stability, but the mount will be more difficult to get through doorways fully assembled.

At this stage you can dry fit everything to check for fit, but don't glue it together yet! The gluing must be done so that parts are aligned correctly with a minimum of twist. The 22 degree fittings make this mount possible. They do not seem to be available around here in sizes less than 1 1/2".

The bottom is made from the Cross or double Teetop and the four 17" long pieces. After dry fitting, smear the inside of each arm on the cross and one end of each arm with PVC glue and pound together as tight as possible with a rubber mallet.

The next item to be carefully joined is the top section consisting of four of the Tees, the two 10" pieces, and two of the 3" pieces. Make sure the pieces are glued to the right spot and are alighed to lay flat. Before starting, make sure the Tees do not have casting "tits", which will prevent making the top assembly lay flat. Some Tees are manufactured in a way that results in an asymetrical side exit. Dry fit this assembly to make sure the asymetry does not result in a impossibly crooked top! Mark which pich pieces should go together. Glue one end of a 10" piece to the side exit of a Tee as shown in the picture above. Glue one end of the other 10" pice to the side exit of another Tee. Now join the ends of the two Tees so the two arms extending from the sides lie flat. One the PVC glue sets in a few seconds, you won't have a second chance to realign! Now work fast and glue another two Tees together with one of the 3" pieces with the side exits dry inserted into the two 10" piece ends. Press flat for a few seconds until the glue sets to achieve perfect alignment. Remove glue, and replace the dry fitted end and press flat while the glue sets. It's not the end of the world if it's not perfectly flat, but with care it is not difficult to achieve.

The legs are made to be easily separated for convenient transportation. Make the 4 legs by gluing a 24" leg into a Tee end as pictured above. Use the mallet while the glue sets to make sure the pieces are seated all the way into the Tee.

The final initial step is to glue a 1 1/2" joiner into one end of each of the four 45 degree elbows, and a 1 1/2" joiner into one end of each of the eight 22 degree elbows (8 of the twelve pictured above).

A 22 degree elbow is now joined to each leg's side exit. When connected with the cross piece already assembled, this provides the flat bottom shelf for the rotator. The angle of the 22 degree exit is critical so I dry insert a small length of scrap PVC into the end of the 22 degree elbow, smear the joiner and Tee exit with PVC cement and press the whole assembly flat to achieve the correct angle as pictured at the left. After the glue sets in a few seconds the small pieces of scrap PVC are removed and I wind up with 4 legs that look like the top two in the picture at the left..

Now I joined the remaining four 3" pieces to the bottom caps and joined the other end of a 3" piece to the free bottom port of each leg Tee. . I just keep them a press fit, because in case of uneven ground where I want to place the mount, I make unequal length bottom legs out of the scrap 1 1/2" PVC to compensate and achieve a vertical mast and flat top. Dry fit the 4 legs to the bottom cross piece and you should wind up with something looking like the picture at the right, but without the top section yet. AFTER the top section is fitted, each of the four 22 degree elbow to cross piece junctions will be drilled for a 1/4-20 bolt and wing nut for easy assembly/disassembly. At this point the mount will look like four oversized 2M verticals on a drunk, leaning towards each other at a 22 degree angle.

The remaining four 45 degree elbows with joiners and four 22 degrees elbows with joiners will be combined and oriented to achieve a near perfect connection with the top section previously assembled. Each of the four 22 degree elbows dry fit to the top of a leg. Later when all the glue is set elsewhere, the four 22 degree elbow to leg top junctions will be drilled for a 1/4-20 bolt and wing nut for easy assembly/disassembly. This next set takes a bit of dry fitting immagination. The four 45 degree elbows are dry fit to the top assembly and the four 22 degree elbows are dry fit to the top of the "drunken legs". The exact orientation of 22s and 45s to achieve the best fit should be marked with a felt tip pen so the pieces (except for the legs) can be convniently glued together.

When satisfied with the fit, glue the 45 joiners to the Tees and glue the 22 joiners to the 45s. When set a few minutes later, you can join the top to the legs, and drill the 8 holes which hold the bolts which fasten the legs to the bottom and top assemblies. Your new mount should look like the picture at the above right.

I used an old CDR rotator mounted on a bottom plate for the azimuth control, and a very old but still running U100 rotator for the elevation. The bottom plate is made from 1/4" scrap aluminum measuring 12" by 12", centered on the cross piece. The CDR must be mounted about 1/4" above the plate to allow for clearance at the terminal strip. A couple of large nuts work fine if you don't have the original thick washers. Drill a 1/2" hole in the bottom plate beneath the terminal strip for the rotator wires to pass through. The plate is held to the cross arms with a 2" U bolt around the PVC (1 1/2" PVC is the I.D measurement).Because of the cross piece bulk, I use four 2" by 3" pieces of the 1/4" plate aluminum as shims between the PVC arms and the rotator plate.

The mast is a 4' long piece of 2" aluminum from a defunct HF beam of yesteryear. I wanted to take the side thrust wind load off the CDR, so I mounted a 7 3/4" by 12" thrust plate from 1/4" aluminum on the top PVC section with four 2 " U bolts. The plate is offset to one side to prove an accessory shelf to be discussed later.I wanted to avoid ant possible noise problem from scraping metal to metal contact, so I put a 4" long piece of 2" PVC inside the 2" metal black pipe flange. Now in PVC, 2" pipe is slightly larger than 2" I.D., which fits nicely around the 2" mast, and about 2 1/3" O.D. A metal pipe 2" measurement is O.D. but still the threads + of the 2" pipe black flange must be removed to achieve a 2 1/3" I.D. to fit the PVC thrust bearing. I bored out the 2" flange to 2 1/3" on my lathe, but a gring bit should work too. In a pinch, a rat tail file should do it in a week or so. After centering the 2" mast, the 7 3/4" by 12" plate was cut out to clear the PVC and the flange bolted to the plate. Make sure the mast rotates without binding. Then the plate is bolt to the top assembly's PVC.

The U100 rotator is unique because the rotating shaft extends through the housing, permitting turning the rotator sideways and with the shaft rotating horizontally, an antenna can be mounted on either side, rotating in elevation. A third plate needs to be built to which the rotator on its side is attached, and the plate attached to the top of the 2" mast with 2 more 2" U bolts. The U100 rotator leads are passed down to the bottom of the mount through the inside of the 2" mast. The U100 rotator does not have much power, so be sure to balance your antenna radially and counter balance it in elevation.

Connect the rotator control heads and you have your new portable satellite mount. The main problem is telling exactly where the dish is pointed. I made 3 things to help set up the mount to locate satellites. The accessory shelf that holds the thrust flange has a special plate holding a bubble level and a compass. I can align the mount in a minute or so. The plate has a thick washer under the middle of the plate which allows the plate to rock in attitude. Four bolts tip the compass and bubble level so that after aligning the mast to vertical in every position, the 4 bolts are tightened and loosened to set the bubble level to level. The compass arrow is aligned so that the mount can be aligned in azimuth perfectly after moving the mount.

The second item is an azimuth position protractor. I made a big one out of 1/4" thick bass wood from the local hobby store. Using a smaller plastic protractor, I callibrated it in 10 degree steps, from 90 degrees (East), through 180 degrees (South), to 270 degrees (West).. I milled a slot in the CDR's bell housing for a calibration pointer. It is easy to set the azimuth with 2 degrees, far more accuracy than needed with a small dish.

The final item is an elevation protractor, of course. Since AO-40 only gets up to 60 degrees high in Colorado, I really only needed 60 degrees, but I made it 90 degrees in 10 degree points. This wooden protractor is glued to the side of the U100 rotator. A pointer made out of a scrap 3/16 copper tubing is held to the rotating elevation shaft with a pair of hose clamps. Like azimuth, elevation is easyt to set within 2 degrees. R2D2 really works great, moves around easily, calibrates fast, and works the satellites fine using the antenna in the following description. May the force be with you.

 

Robert W0LMD