The antenna rotor
An antenna rotor - what for? To improve reception!
Antenna rotation systems open up new possibilities: With a rotor, you can turn a directional antenna exactly in the direction from which the signal with the best signal-to-noise ratio comes. This makes the desired signal (useful signal) louder and easier to understand. Your radio connection becomes more reliable and secure. An antenna rotor is the prerequisite for using a directional antenna, because only with it can you also align a directional antenna.
Why a directional antenna?
A directional antenna allows you to reach distant stations because directional antennas are more powerful: They have a longer range, a better signal strength that prevails over other signals and thus ensures better intelligibility, even with weak signals.
For whom is an antenna rotor suitable?
Antenna rotators are suitable for radio amateurs and shortwave listeners who want to install a rotatable directional antenna on the roof or in the garden. All you need is the possibility to set up an antenna system on a building or property (home, company, farm, garden hut in the allotment garden).
Of course, it is also possible to use a portable antenna system: The mobile version is particularly interesting for radio amateurs who want to set up an antenna with friends in the countryside for a short time and transmit.
If you live in a flat and cannot get permission to install an antenna system, you still don't have to give up radio: You can set up a system at another location and use interfaces to transmit from home.
What antenna rotor systems are there?
Basically, there are two types of rotor systems:
The Azimuthal System
With the azimuthal rotor system you can only rotate your antenna 360° parallel to the horizon, but not in elevation to the sky.
The Elevation/Azimuth System
This rotor system uses two rotors: one rotor allows 360° rotation in the azimuth direction, the other allows elevation in the elevation direction. You need such an antenna rotor for satellite radio because the signal comes from above.
How is an antenna rotor mounted?
You have two options: You can operate the antenna rotor with or without a top bearing. With a top bearing, you can safely set up much larger antenna systems, but the construction is more complex.
1. standpipe | 2. rotor with upper clamp set | 3. platforms | 4. lower clamp set | 5. upper bearing | 6. rotary tube | 7. roof duct (lead tile)
Without upper bearing
Here, the rotor is placed on a fixed standpipe, which is mounted on a wall or in the roof truss. On top of the rotor is a rotating tube that carries the antennas. When it is windy, the antennas (depending on the area of the antennas) offer resistance to the wind. This creates a force (the bending moment) that acts laterally on the rotor. This force is all the stronger the longer the rotating tube is (leverage).
Without an upper bearing, the rotor must be able to absorb this bending moment (= wind force x lever force) completely on its own without being damaged.
With upper bearing
The antenna rotor is used together with another bearing. This is fitted at the top and is therefore called the upper bearing. The rotating tube goes through the upper bearing and ends in the rotor, which sits further down. This construction significantly stabilises the system and allows it to withstand much more wind power. The decisive factor here is the distance between the upper bearing and the rotor: the greater the distance, the more force can act on the antenna without causing damage.
However, the construction effort increases with an upper bearing - additional components are needed, such as a standpipe, lattice mast, platform for the upper bearing and so on.
Buying an antenna rotor - but which one? What to look out for?
If you want to use an antenna rotor, you must make sure that it fits the physical conditions such as wind strengths, antenna size and weight so that the safety of the antenna system is guaranteed.
The main selection criteria for a rotor are load-bearing capacity and torsional and bending moment. These values limit the maximum height and size of the antenna system and the number of antennas.
What is the maximum weight of the antennas together with the rotating tube and all cables? The load capacity indicates the maximum weight of the antenna system above the rotor. This value is independent of whether the system is set up with or without upper bearing. It is measured in kg (kilograms).
how much wind can the antenna rotor take?
The bending moment defines the maximum lateral force that may act on the rotor between the upper and lower ends of the rotor. The moment is given in Nm (newton metres) and is made up of the wind area, i.e. the area on which the wind can impinge, the maximum wind force to be expected and the length of the rotary tube. This value is highly dependent on whether the system is installed with or without a top bearing.
what mass can the rotor turn?
The torque is the maximum force of the rotor to turn and also to brake an antenna system. A large and heavy antenna system has a large mass and therefore a large inertia to overcome. If the antenna is too large and heavy for the rotor, the motor or the gears of the rotor may break down. Information on this can be found in the technical data of the rotor.
When the desired direction is reached, the entire mass must be braked again; the force required here is the braking torque. In order to come to a standstill during the braking process, the torque = braking torque. The torque is given in Nm (newton metres).
what if the wind wants to turn the antenna?
The braking torque is not only the force it takes to stop a rotational movement. - It is also the force that keeps the antenna in position when the wind wants to turn the antenna. This can be the case if the antennas on the left and right of the rotating tube are unevenly sized. The force it takes to keep the antenna aligned against wind forces can be quite a bit greater than the force that slows down the rotor-controlled antenna rotation.
What needs to be considered here?
Does the rotor drive also brake unwanted rotation from standstill? That depends on which drive system the rotor uses: Gearboxes with a worm drive also serve as a brake, but gearboxes with gears still need an additional mechanical brake.
Further selection criteria for the purchase of an antenna rotor
So a slow acceleration and deceleration of the rotational speed? This is important, because if a heavy antenna system is jerkily slowed down or accelerated, enormous forces occur, so that damage can occur.
The indication of the compass direction can be displayed in different ways, which have different advantages and disadvantages depending on the user's needs.
1. the pipe diameter: the diameter determines the stability of the installation: thin pipes can carry less.
2. the rotation range: of course, the rotation range should be at least 360°. A larger turning range is more comfortable, because you don't always have to go completely around.
3. the rotation speed: complete rotation takes 45 seconds to 2 minutes, depending on the rotor model. If a rare station can only be reached for a short time, then a fast rotation is of course an advantage. Don't forget: the faster you turn the more violent the impulse is when braking....
Remote-controlled stations have become increasingly important in recent years. Radio amateurs who cannot set up an antenna system at home also want to use the radio. For this purpose, they operate a radio system together with friends, for example in a clubhouse outside. This is a great way to transmit without interference from the city. To do this, the entire station must be controllable via the internet: the radio must be operated, the received audio signal as well as the transmission signal must be transmitted and the rotor must also be operated. There are many programmes that facilitate and support this. The technical prerequisite for this is a control unit that supports remote controllability.
The control unit of an antenna rotor
Why is a control unit important for the operation of an antenna rotor?
An antenna rotor cannot be operated without a control unit. Basic models are usually supplied. The minimum requirements for a control unit are: Power supply, sensors and display for the current direction, as well as operating elements to control rotations.
Optionally, there are connection possibilities for remote control. For retrofitting, there are control units that enable much more comfortable radio control. For example, the possibility to save directions or the preselection: here the control unit takes over the entire rotation, i.e. smooth starting, turning and braking at the target. We describe details below.
Make sure that the rotor and the control unit match!
How do I operate the control unit of an antenna rotor?
There are three ways to operate the rotor or the control unit for it:
- manual
- semi-automatic
- automatic
Manual control units are the simplest version of a control unit: when turning manually, the button for left or right rotation is pressed and held until the desired direction is reached. You have to keep an eye on the display during the turning process and check how far the antenna has already been turned. This may well take two minutes. If you have overshot the mark, you have to steer back manually.
Semi-automatic control units offer the possibility to pre-select a direction. All you have to do is press the start button and the antenna moves automatically to the preselected position. You do not need to constantly look at the display, but can devote yourself to the radio again.
Automatic control devices or the connection to the computer are particularly convenient:
You can select a stored direction or the computer automatically selects the best direction based on the callsign or QTH locator entered: You can enter Japan and the antenna will automatically turn in the cardinal direction stored for it.
For connections via low-flying satellites that move very quickly across the sky, fully automatic tracking is indispensable: Here, a programme on the computer calculates the flight path for the desired satellite and automatically tracks the antenna direction.
Can I control my antenna rotor remotely via the internet?
Yes, this is possible without any problems.
Higher-quality control units have the corresponding connections. With simpler or older models, you have to connect the cables manually.
What are the advantages and disadvantages of the different control units?
Unfortunately, the simplest antenna rotor models do not have a direct connection option to the computer. You can upgrade with an external interface.
The connections between the actual control unit and the computer interface are usually very simple: you only have to identify the contacts for left and right rotation on the control unit and connect them to the interface, as well as the direction signal. Suitable interfaces for upgrading control units are: the ARS USB AZ/EL interface from EA4TX or the RTC-200 from CG-Antenna.
No, absolutely not. There are controllers from microHAM, EA4TX, CG Antenna or MFJ that replace the original controller and offer more comfort.
Alternative control units for the rotor, i.e. control units from another manufacturer, are usually very easy to install: Take off the old unit, put on the new one!
MFJ offers, for example, the digital controllers YRC-1 and YRC-3 for different rotor types. These can also be used without having to rework the cable. Other advantages are the USB interface and the digital display, which is less error-prone than its mechanical predecessor.
The most sophisticated control device is the ARCO controller from microHAM. This device is very powerful and also works without the PC next to it. There are even Ethernet interfaces available. The ARCO controller has very extensive connection options for a wide variety of rotor types. The connection to Yaesu rotors is especially easy, because you don't even have to change the plug on the cable.
The ARCO has features such as direction preselection, memory, adjustable rotation speed, map display centred on your own location (great circle display, beam map), distance display, touch screen. It is also extremely robust and can even withstand a short circuit.
With this antenna rotor, you can transmit very comfortably and completely independent of a computer.
Antenna rotor accessories
What should be considered when selecting rotor control cables?
Cable cross-section
Each rotor manufacturer specifies a different number of cores in the cable: Yaesu uses five or six cores, Hy-Gain six or eight, other manufacturers even use ten cores.
It is important that the thickness of the cores matches the length of the cable: The longer the cable, the thicker the cores should be! You can easily lay cables with a length of 50m or more, but the cable should have a cross-section of at least 0.5mm², even 0.75mm² would be better.
Solar radiation
You should protect the rotor control cable from sunlight! Note that not every cable is inherently well equipped against UV radiation.
Connector
The matching plugs are usually supplied with the antenna rotor.
Which accessories for antenna rotors and control units are useful?
The accessories required depend on the type of structure you want:
- For a rotor with upper bearing, you need the upper bearing itself and one or two rotor platforms for mounting.
- For somewhat uneven floors, there are compensating plates, which also dampen the sound of the motor at the same time due to the rubber bearings.
- Most rotors are supplied with only one set of clamps (for the top), which is sufficient for mounting on a platform or on the floor. However, if the rotor is to be mounted on a standpipe, it is essential to have another pair of such clamps for the bottom.
Are there any questions left unanswered?
Contact us - we will be happy to answer your questions.
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