11211 - 154
Street, Edmonton, AB, T5M 1X8
It is the policy of AlfaRadio Ltd. to use SI (Metric system) in its measurements where possible.
SI is the standard method of units and measurement in all but
three counties in the world.   See SI standards
Conversion to the old Imperial units is possible see
SI Units: SI - - International_System_of_Units
Bureau_International_des_Poids_et_Mesures Home page
A poorly defined non-standard value used to express the loading on an antenna due to wind,
typically expressed in pounds per square inch or square feet.
This often does not take into account:   density of air due to humidity, elevation, airborne particles such as sand,
water and ice as well as several other factors such as icing on the antenna.
It is a poor method of determining the loading on an antenna or rotator due to the non-standard way
in which manufacturers rate the antennas and rotators.
If there were a standard method of defining the way to measure this value and if all manufactures used this method, then it would be OK.
Torque:   Nm An explanation of Torque
The standard unit of Mass (kg is NOT a unit of weight see Newton)
Newton:   N A derived unit of force.
These links may provide some insite to the problem:
ARRL - QEX
NRC - Canada
Some things to consider when reviewing rotators and /or antennas:
- Antenna wind load is fine to determine if your tower and/or mast can survive, or a rotator if it is mounted outside the tower.
- Wind load ratings do not address how symmetrical the wind balancing is.
- If wind was straight, there would be no horizonal torque (if antenna was wind balanced.) only vertical torque on the mast.
We know this is not true.
How can you account for the swirling factor of wind?
- It does not say anything about the momentum the antenna builds up from its' movement in the wind.
This is in addition to the force from the wind.
- Momentum or flywheel effect needs to be taken into account:
the weight and mass of the antenna,
and how far from the center it is mounted,
and how fast it is moving.
- The momentum and/or flywheel effect is the shock load that breaks rotators.
- You can have several antennas with same windload but they could have vastly different rotational torque profiles when measured at the rotator joint.
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This was was last updated 04Feb2014>
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