# Polarisation of man made noise – an 80m case

Polarisation of man made noise discussed an explanation for the common observation more ambient noise is captured by a vertically polarised antenna than for a horizontally polarised antenna.

This article documents an analysis of a case on 3.6MHz and is to be read in the context of Polarisation of man made noise. Remembering that P.368-9 publishes a set of graphs like the one above, and that they show that ground wave attenuation is dependent on distance, soil type and frequency.

Though ground wave attenuation is lower on 80m than 40m, the horizontal antenna used in the example is at a fixed height, so it is electrically lower on 80m which increases horizontal attenuation significantly.

Again, let us assume that the total man made noise captured by a receiving antenna is due to a large number of small sources distributed evenly around the receiving antenna.

This analysis will use the propagation loss according to P.368-9 (using GRWAVE.EXE) to calculate the contribution of distributed noise sources around the receiving antenna.

## 3.6MHz example

Let us assume that vertically polarised waves are radiated from the distributed noise sources and captured at the receiving antenna.

The following analysis assumes:

• vertically polarised ground mounted monopoles of 10m height;
• ground parameters σ=0.005,ε=13 (different to the graph above);
• sources within 200m radius are excluded (near field effects excluded). The graph above shows that the contribution of source falls with distance, initially quite rapidly, and this is due to a combination of inverse square law effects and surface wave attenuation due to the ground medium.

We can perform the same analysis for horizontally polarised waves

The following analysis assumes:

• horizontally polarised dipoles at 10m height;
• ground parameters σ=0.005,ε=13 (different to the graph above);
• sources within 200m radius are excluded (near field effects excluded).

We obtain a similar result, but attenuation is significantly higher and more so if the dipole heights are reduced.

Combining the vertical and horizontal results, and assuming for the moment that noise sources are of random polarisation with equal RMS vertical and horizontal components… The plot above show the cumulative power captured for the Vertical-Vertical case and Horizontal-Horizontal, normalised so that total power captured V-V is 1.

Note that 90% of the captured power for the V-V case is from sources at less than 1100m distance. The power captured for the H-H case is much lower (~31dB) and 90% is from within a 600m radius.

Ground wave attenuation means that most man made noise arriving by ground wave is very local, less than 1100m in this scenario, and higher ground wave attenuation of horizontal waves results in much lower noise capture at a horizontal receiving antenna.