Dish Rotators

A dish needs to be moved in elevation and azimuth to track satellites such as AO-40. Old TV rotators are fine for BBQ grill dishes and small yagis, but the bigger the antenna, to more power is required, of course. 5' and larger TVRO dishes typically use linear tracker arms for elevation. Azimuth is a bit more complicated. It is best to radially balance and counter balance the dish if you want the rotators to survive occasional storms. Most big dishes are parked looking upwards. A big dish at 0 degrees elevation develops a great amount of twisting torque in a windstorm. In snowy areas, like my QTH, a dish parked looking upwards can crush the mount in a heavy snowfall. A solid dish can hold many gallons of water in a rainstorm. As a result, I park my solid 14' dish at about 50 degrees elevation facing downwind, which lets the water run out and won't accumilate much snow. One time I had it at 60 degrees, and got showered with about 10 gallons of water after a storm. Another consideration is avoid wrapping the coax around the azimuth shaft in a windstorm. I put stops on my 14' dish after it tore up some expensive coax in a storm. The stops limit azimuth rotation to about 300 degrees, fine for AO-40 and EME.

TV antenna rotators

CDR and Alliance U-100 rotators are good for small amateur antennas like a barbecue grill dish and a small 435 MHz yagi. A hubcap dish would work well too. The U-100 has a unique construction in which the rotating axis goes all the way through the body of the rotator, making it ideal for use as an elevation rotator. Two problem occur, however. The Antenna mount is then horizontal. But by making a 1/4" aluminum plate, the 4 original mounting bolts and two U bolts can be used to attach the rotator body to a vertical mast. The other problem is that the rotator was made waterproof when in the vertical position.

The CDR family of rotators make nice units because the housing is bell shaped, making them quite rugged and waterproof. Other TV antenna will work quite well too.

Most of the small TV antenna rotators have a remote control box that either reads out in degreees on an analog meter, or has a solenoid stepped indicator. Either works fine for the wider beamwidth of small dishes and yagis, and slow moving satellites like AO-40. But manually tracking the LEOs can be a real challenge.

Often these older rotators will be sluggish or inoperative. The motor in these rotators operate from 2 phase AC. The most common problem is the phase delaying AC capacitor going bad. Replacing the capacitor usually completely restores the rotator. Finding the AC capacitor can be a problem, though. In a pinch a pair of DC capacitors at double the needed capacity, back to back, can be used

Ham-M series rotators

can be used to turn small to medium sized dishes in azimuth. The main difficulty is that the brake in these rotators steps the dish in very coarse steps. The earlier Ham-2 has a finer brake that steps in about 3 degree steps. The later Ham-4 has a stronger brake with fewer teeth. The result is that the Ham-4 steps in 4 degree jumps. A 7 1/2' dish with a beamwidth of 5 degrees would be marginally acceptable when turned in Azimuth by a Ham-2..

Using a HAM-4 Rotator to Turn a 7 1/2' Dish by KC9GI

Bill sent me several SSTV pictures over AO-40 showing his 7 1/2' dish installation. AO-40 superimposes a lot of QRN on the pictures, due to some 435 MHz RADAR signals (which also cause Leila to bleep when nobody is there!) Bill uses the standard 3 1/2" steel post in 3' by 3' of concrete. The Ham-4 is mounted alongside on an angle bracket bolted to the post. At the top of the post is a 2" flange bearing on another angle bracket which supports the weight and side thrust of the 7 1/2' dish. The mast is a piece of 2" heavy wall steel tubing. The I.D. of the 7 1/2' dish's top cap is 3 1/2", so a 2" to 3 1/2" adapter is placed at the top of the 2" azimuth rotating mast. The dish will only go down to 3 degrees due to interferrence between the lower dish rib and the top of the mounting post. If the top post was on the North side instead of the South side this interferrence would not occur. The feed for the dish is a 2 1/2 turn helix, mounted on what was the back of the Chaparrel feed. The original LNA plastic cover is used to cover the 2401 MHz downconverter now. The HAM-4 brake has 75 segments, spaced 4.8 degrees apart. This results in the dish "stepping" in 4.8 degree jumps when the brake wedge engages. Bill says this has not been a problem. The older HAM-2 brake had 96 segments spaced 3.75 degrees apart. The rotator turns 360 degrees in under a minute, a bit fast for precise pointing. But it's way ahead of taking a "moving the dish" break every 10 minutes! Manually tracking AO-40 has not been any trouble for Bill, but when he tried tracking a LEO satellite, it was a real handfull.

Bill also found out some info on the Ham series rotators: "M"--96 segments--3.75 degrees apart--rotation time approx. 50 seconds "II"--96 segments--3.75 degrees apart--roatation time approx. 50 seconds "III"--96 segments--3.75 degrees apart--rotation time approx. 50 seconds "IV"-- 75 segments--4.4 degrees apart--rotation time, 45-60 seconds "TAILTWISTER"--60 segments--6 degrees apart--rotation time, 45-60 seconds This info from KM5FL, NICK--who rebuilds Ham series rotators.

This post in the ground supporting another rotating post is a great sytem that would also work well for sprockets, chain, and gearmotor rotators. It would be a good system to consider with the mounting pipe stub obtained when removing the mounting post top, less concrete part, of a free dish.

Yaesu G-5400, G-5600, & G-5500

are great if you want a turnkey satellite tracking set of rotators. The older G-5400 and G-5600 are North centered on the azimuth meter. It is at a disadvantage when working AO-40 in the Northern Hemisphere because when the satellite crosses 180 degrees the rotator must turn around 360 degrees to pick it up on the Western side of 180 degrees. The G-5600 is similar to the G-5400 except that the azimuth rotator has twice the power of the azimuth rotator in the G-5400. The G-5400 would be at risk if carrying a Primestar dish in a heavy wind. The latest version is the G-5500. This unit has the power of the G-5600 and has a South centered azimuth meter, making it the most desireable for use with AO-40 in the Northern Hemisphere. It also has 450 degrees of azimuth rotation. This can permit non-flip coverage for N-S LEO satellites. The analog meters in the Yaesu rotators are small and difficult to read. The friendly price on a new Yaesu G-5500 is around $625.

Linear Arms

became very popular on TVRO dishes 15 years ago. They are an all enclosed screw thread mechanism with a small DC gear motor turning the threads in or out to move the dish's polar axis across the Clarke belt. A magnetic sensor sends a signal back to a computerized controller that has been programmed with how many pulses it takes to go from satellite to satellite. They can work quite well as an elevation rotor if confined to 110 degrees movement or less. Tracker arms come various lenths and power. The smallest arm I have seen was about 10" but the usual throw on TVRO arms is 18" to 24", occasionally 30". The longer the throw, tghe more expensive. The motor on the should draw about 2 amps at 18VDC when run in either direction. If the current is significantly larger, or the motor won't run at about 12 VDC, the motor is bad. Usually these tracker arms have limit switches that prevent jamming on either end. Mount the arm on the elevation axis so you derive the maximum throw for 60 degrees elevation (70 degrees for EME). Mount the so the body hangs down and the motor is up to prevent water damage. You will need maximum torque at about 30 degrees elevation, so set the attachment points so that the linear arm is puhing sstraight out at that point. Satellite shops usually have a supply of these things at little or no cost, as the newer digital satellite antennas don't move around.

Sprockets, Chain Drives, Pulleys and Gearmotors

can provide azimuth rotation with off the shelf parts. A large sprocket is attached to the revolving top cap and a small sprocket is attached to the gear drive. A chain connects the two sprockets. Motorcycle sprockets come in various sizes. Another source is bicycle shops. Bicycle chains would be smaller with a lower breaking point. Another source of sprockets is Go-Karts. Some Go-Kart sprockets are made in 2 parts that allow attaching the sprocket to the top cap without removing the heavy dish from the post. Chains come in several sizes popular sizes from #25 to #70. Each size has a standard breaking strength. #25 is too small and # 70 is too big for TVRO dishes. But a #40 chain (bicycle size) is good for up to a 7 1/2' dish, and a #50 chain (motorcycle size) is good for a 10' to 16' size. The smallest size is sometimes available in plastic. This plastic chain and sprocket set would work well for coupling an azimuth or elevation potentiometer to its axis. Using a set of pulleys and a V belt off the gear motor will provide a slip joint in case your big dish is hit by the local hurricane. A high wind turned my 10' dish 110 degrees one time, but since the azimuth position potentiomer was atached to the chain's small sprocket shaft, I didn't even loose calibration.

I recently got a sprocket and chain set from a local Honda Motorcycle Shop. The set was made for125 cc "Enduro" motorcycles, so will definitely last forever! The large sprocket had 45 teeth, and the small sprocket had 12 teeth. The chain came in a "120 link" lenght and was called a "520" chain. It is roughly equivalent to #50 chain, with about 1/2" spacing between the teeth, but the teeth are narrower so the chain is narrower than the #50 industrial chain. The 45 tooth large sprocket has a 5" hole in the center which provides plenty of clearance for the rotating top cap of the dish mount. The large sprocket is held to the top cap by attaching some 2" square aluminum tubing to the top cap and large sprocket. The small sprocket has a slightly less than 3/4" center hole with splined teeth. A piece of 3/4" threaded rod is just slightly larger than the openining in this small sprocket, so I put a 3/4" nut on one end of the threaded rod, tapped the small sprocket onto the rod, and placed a locking nut on top of the small sprocket. It will never turn or loosen. A pair of 3/4" two bolt flange bearings complete the assembly.

      AC motors are used on the various Yaesu, Ham-M and TV antenna rotators. DC motors are used in the dish linear arms and gearmotors. The AC motors have the advantage of non-sparking while running. I have not not noticed any spark noise from my DC motors on dishes which are looking away from the spark source. I do notice extraneous pulses occuring when either the AC or DC motors first turn on, which make the analog potentiometer voltages jump. Long cables on a Yaesu rotator will result in picking up of commonmode spark pulses. Putting the motor lines in one cable and the analog meter lines in another shielded cable, with separation, should reduce the problem. Be sure to attach the shield at only one end, preferrably the rig end.

Gearmotor

is a motor and a gear unit integrated into a single package. AC gearmotors are typically a single set speed, but a DC gearmotor usually has its speed set by the voltage level. I like the azimuth and elevation axis speed to be about 1/dish size in feet RPM for my dishes. A 10' dish should move its elevation and azimuth axes at 1/10 RPM. If you have a 48 tooth sprocket on your top cap, and a 12 tooth sprocket on the gear motor, this is a 4 to 1 gear reduction, so you would need a 2/5 RPM gearmotor. If the 12 tooth sprocket is fed by an 8" pulley with a V Belt connecting it to a 2" pulley on the gearmotor you wind up with a 16:1 ratio, and a 1.6 RPM gearmotor would be needed. Often the sprockets and pulley sizes are set by the gearmotor on hand. Generally, the slower the gearmotor, the more expensive. A 1/30 HP gearmotor is fine for up to a 16' dish. The gearmotor must be able to run in both directions. A DC gearmotor can be reversed by simply reversing the polarity of the the leads.The DC gearmotor is easy to limit switch protect by placing a limit switch at each end of travel with a properly polarized diode across each limit switch. This way the motor travels to the end and stops, but when the voltage is reversed, the diode conducts and the motor starts up in the opposite direction. Reversing an AC gearmotor is not quite so simple, but possible.

I recently visited Surplus Center in Lincoln, Nebraska (800-488-3407). This is an excellent source of industrial chain, small sprockets, 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. Another source of gearmotors is Grainger http://www.grainger.com/catalog .Industrial chain and sprockets tend to rust in outdoor usage, so local Motorcycle, Bicycle, and GoCart stores are your best local source. Motorcycle parts are expensive but built to take abuse.

A pair of Linear Tracker Arms

can be used to move a medium sized dish in azimuth. Each arm is able to move about 100 degrees, so the pair operates against a common idler arm to provide about 200 degrees of azimuth rotation. 200 degrees is fine for AO-40, but marginal for EME. THe two tracker arms are wired in parallel so that they will open and close together. The arms must each be equipted with limit switches as they may not run at the same speed. A third tracker arm moves the dish in elevation. There is a picture of my three Tracker arm systme in the section showing my various diish projects.