Polarisation Mismatch
If there is an angle theta between two linear antennas, the resulting loss is calculated with 20*log10(cos theta): approximately 1.2 dB at 30 degrees, 3 dB at 45 degrees, 6 dB at 60 degrees. At 90 degrees the theoretical loss is infinite; in practice, because of reflections, it stays on the order of 20-30 dB and the range drops dramatically.
This loss goes straight into the link budget and can be recovered at no hardware cost. By the 6 dB rule, a mismatch of 60 degrees alone halves the range.
- The most frequent mistake: mounting the receiver antenna horizontally on the enclosure while the remote control is held upright.
- The second most frequent mistake: bending the antenna to one side and fixing it there after it has been brought out through the cable gland.
- Diagnosis is easy: turn the antenna by hand and observe the difference in range or signal level.
Field practice can be summed up as follows: fix the receiver antenna vertically and tell the operator to hold the remote control so that its antenna stays upright. The habit of holding the body of the remote control horizontally shows itself as intermittent response, especially in installations working at the range limit; this is a problem often taken for a fault but entirely geometric.
Context in which this term is used: Wireless remote control installation: pairing, relay, safety