So your satellite dish no longer moves East-West?
Or perhaps it is intermittent?
I keep getting asked this sort of question:
"My dish no longer moves east (or west). Is it the reed at fault?"
Obviously I can't guess so you'll have to carry out some basic tests. See below.
"I had to disconnect my positioner/receiver but couldn't be bothered to keep a note of the wire colours. Which colour goes where? I have lost the handbook."
There is no colour standard for the wires so you'll have to look inside the motor and note which wire goes where. Normally, there's two thin ones connected to the magnetic reed switch and two thick ones connected to the motor (via diodes and microswitches).
Both pairs of wires are supposed to be separately screened in order to prevent electrical noise, from the motor, from getting into the reed switch wires - otherwise the extra interference "pulses" can make the positioner think that the dish has moved further than it actually has. In addition, the interference can be so bad that the motor wires act as an aerial and cause interference on neighbouring TVs and radios each time you move the dish. How would you like the Radiocommunications Agency knocking on your door with a summons? Lots of cowboy installers use ordinary four-core "caravan" cable or, worse, telephone cable. You might get away with this for short runs but don't be surprised if you suffer from intermittent problems such as interference, loss of position and neighbours knocking on your door.
Motorised systems are rare, nowadays, so the proper "screened ribbon" cable is hard to find (and expensive).
If you connected the wires to the positioner terminals incorrectly then, dependent on *what* you connected and *where*, there are three possibilities:
- 1. you damaged the reed switch in the dish motor unit
- 2. you damaged the positioner unit.
- 3. or both.
You can test the dish motor without climbing a ladder by connecting a known good positioner to it. Any competent installer of motorised equipment can do this and should not charge more than the call-out charge. (If you go for a "free call out", expect to get what you pay for!)
To test the dish motor yourself you will need the following:
- Two fully charged 12v lead acid batteries connected in series to give 24 volts.
- (car batteries or alarm batteries will do, or a 20v - 30v DC supply capable of supplying 4 Amps surge and 2 Amps continuous).
- Two 5 Amp fuses in holders (as used for car radios)*
- A Light Emitting Diode (LED).
- A 1 k Ohm resistor.
- Some 2 Amp insulated wire.
- A switch
* The circuit will work without the fuses but they should be fitted (close to the battery terminals) for your safety.
/
,-----/\/\/\-----/ -----------------> To thick motor wire M1
__|__ 5A fuse 5A switch
| + |
| | 12v battery
| |
__-__ + -
|-----/\/\/\---------------|>|------> to thin pulse wire P2
__|__ 1k resistor LED |
| + | |
| | 12v battery | test only*
| | |
__-__ |
| V
'-----/\/\/\------------------------> To thick motor wire M2
5A fuse |---> and thin pulse wire P1
DO NOT CONNECT THE RECEIVER/POSITIONER!
Connect the batteries as shown.
Before you connect the motor, connect the test wire*
The LED should light. If it does not, reverse its connections and test again.
Now remove the test wire*
Now connect the motor as shown.
It doesn't matter if you mix M1 and M2 or P1 and P2 provided that you don't mix thick and thin wires!
Close the switch. The dish should move and the LED should flash.
If the dish moves but the LED does not flash, the motor reed switch is probably faulty.
If the dish does not move it may be in its extreme position.
Reverse wires M1 and M2 and try again.
If the dish moves and the LED flashes for both directions of movement then the dish motor is OK and the magnetic reed switch is OK.
| Dish cables must be shielded. If the sensor cables are not correctly shielded then you can't expect a positioner to work reliably. If you found one that does, that was lucky. It probably has good input filtering. The longer the motor cable, the higher its resistance and the LESS current the motor can draw. The motor will run more slowly, which is generally a good thing. However, a long *unshielded* sensor cable is very BAD news. Here are some basic "ground rules" (excuse pun!):- Long cable is good because it slows the motor and therefore the pulse count is slower and easier for the positioner to handle. (I've heard of problems - especially with Jaeger H-H - where the thing went so fast that the positioner lost count. Answer was to fit a resistor in a motor wire to slow it down.) Properly grounded shielding is essential because: 1. It stops the motor interference from being counted along with the real pulses or, from *blanking* some of the real pulses (unusual but possible). 2. Shielded motor cable stops the motor from interfering with other equipment (including neighbour's TV !) 3. It stops the motor from intefering with the polariser current (if any) which can cause weird effects, albeit usually temporary. The cable shields should be connected to the ground terminal (GND) at the positioner. They should NOT be connected to the metal parts of the dish. |
| The dish metal parts should be grounded separately. The whole point of earthing a dish is to get rid of static charge that builds up when charged particles (eg. dust) are blown across it. As a secondary measure, a GOOD earth might help prevent damage inside the house in the case of a nearby lightning strike (but not a direct hit unless you use solid copper bar at least 25mm diameter!) Hammer a long copper rod into the soil and use the thickest wire you can find to connect it to the dish. Use bolts, not solder. DO NOT earth the dish to any house wiring earth cable. This is a good way to get lightning or static discharge into the house. The LNB should be mounted in an insulating clamp. The LNB coaxial cable is connected to the receiver ground via the "F" connector only. It should NOT be earthed outside. All motorised cable shields should be connected to the ground terminal at the rear of the receiver/positioner only - NOT to the dish. This is the best compromise to ensure safety and freedom from interference caused by the dish motor. |
| VOCABULARY Actuator = Linear Actuator = Dish Motor. This is the "telescope" that pulls and pushes the dish. Positioner = ACU = Antenna Control Unit. This is the box that supplies current to the Dish Motor. Sometimes it is *inside* the receiver. It contains a power supply that can supply 24 to 36 volts at 2 to 4 Amps. It contains a circuit that supplies a small voltage and current (usually 5 volts at a few milliamps) to the magnetic reed switch inside the Actuator. When the motor turns, a spinning magnet forces the reed switch contacts to open and close. A circuit inside the Positioner will count the pulses that come from the reed switch and so determine the position of the dish (relative to where you set the "limit" or "start point".) |
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Updated on February 18, 2000
liner actuater should be linear actuator
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