What is antenna polarization, must the remote and receiver antennas point the same way?
Polarisation is the antenna's field direction. An axis error costs 3 dB at 45 degrees and 6 dB at 60; 6 dB halves the range. Keep the antennas upright.
Polarisation is the direction of the electric field the antenna produces. If there is an angle between two linear antennas the loss is 20*log10(cos): 3 dB at 45 degrees, theoretically infinite at 90 degrees and 20-30 dB in practice. That is why the remote control and receiver antennas should be kept on the same axis as far as possible, typically vertical.
How much loss at which angle
| Axis difference | Loss | Effect on range |
|---|---|---|
| 0 degrees | 0 dB | Full match, no loss |
| 30 degrees | 1.25 dB | Not noticed in the field |
| 45 degrees | 3 dB | Range falls to about three quarters |
| 60 degrees | 6 dB | Range falls by half |
| 90 degrees | 20-30 dB in practice | The link drops on most sites |
It is no coincidence that 6 dB halves the range exactly; the 6 dB rule describes the price of doubling the distance. By the same logic a loss of 20 dB brings the range down to roughly a tenth. Polarisation mismatch can be enough on its own to explain the range even when every other item in the link budget is correct.
How it is applied in the field
- Mount the receiver antenna vertically; the antenna of a handheld remote control also stays largely vertical during use.
- Plan the antenna placement before the panel is mounted; trying to correct it afterwards with a cable brings extra loss.
- If the operator carries the remote control horizontally on their belt and presses the button, a drop in range is normal and not a fault.
- Raising the antenna is no substitute for correcting the axis, but the two work together: an antenna that stands vertically and rises above the obstacle usually gives a better result than a horizontal antenna that has merely been raised.
Frequent installation mistakes
- Fixing the receiver antenna horizontally on the side face of the panel. It is a classic mistake and creates an axis difference on its own.
- Turning the antenna downwards for the sake of appearance; this spoils both the polarisation and the radiation pattern.
- Leaving the antenna inside a metal panel. In that case correcting the polarisation does not change the result; the antenna has to be brought outside first.
- Closing your palm completely around the device when the remote control's antenna is inside the housing. The hand both attenuates the antenna and shifts its effective axis.
How to check the axis in the field
No instrument is needed. Stand at the point where the range drops and give the same command first with the remote control held upright and then turned horizontal. If the response comes in the upright position and not in the horizontal one, you have seen the effect of polarisation directly. Do the same test for the receiver side as well: bring the antenna temporarily to vertical and try again from the same point. If either of the two tests makes a difference, the answer lies on the mounting side and the permanent correction is a few minutes' work.
What polarisation does not explain
In metallic environments such as a crane cabin, reflections partly scramble the polarisation; this is sometimes a loss and sometimes a rescue, but it is not reliable. On sites where multipath propagation dominates, correcting the antenna axis may not give the gain you expect. If the range complaint grows as the battery weakens, if it is seen only while the inverter is running, or if it started after an antenna extension cable was added, the cause is not polarisation; look at the battery, the source of interference and the cable loss in that order.
On a range complaint, checking the axis of both antennas before taking any measurement is the cheapest diagnosis and needs no part to be changed. If the axis has been corrected and there is no difference, carry on searching in order: the battery level, the position of the receiver inside the panel, the antenna extension cable and the sources of interference around it. Breaking this order usually ends with an antenna or a receiver being changed for nothing.
The full topic: 433 MHz or 2.4 GHz?