by MD0MDI

_{t} is the gain of the transmitting antenna, P_{t} is the transmitted power, and MF HF Groundwave Model – Equation 1a[/caption] is power flux described as the measure of Watts divided by area at the distance R meters from the transmitter [2].

_{e}). This is the area that captures a quantity of power flux and converts it to power [2][3].

The power available at the receiver, discounting feeder and other losses, is described by:

*As an aside, the effective capture area of a dipole has been found to be (3 l ^{2 }/16 p) ~ 0.119 l^{2 }which can conceptually be thought of as a circle at the radial distance of l / (1.6 p) from the dipole centre [3]. The physical significance of this is that a sphere of approximately this radial distance surrounding the antenna can be thought of as enclosing the reactive (or near-field) whilst the region outside the sphere contains the radiative (or far-field).*

*As the radiation propagates further into the far-field the radiation front tends to become linear and the flux lines tend towards being parallel. E.g. light emitted from a star can be considered as parallel rays on earth and the wave front can thought of as linear rather than spherical. A camera lens is said to be focused at infinity when all light rays seem parallel to its axis and this occurs at distances much closer than most people would think.*

Where is the intrinsic impedance of free-space (~ 377 ohms).

Where G_{h} is the height gain and L_{t} is the total loss due to radiation.

_{p} is the total loss over the path. L_{f} is the free-space propagation loss, which takes into account the inverse-square law. L_{g} is the ground loss, and L_{m} contains other losses which will be described by the new propagation Model (introduced in reference [1]). For the traditional propagation model L_{m}=0.

**Free Space Propagation Loss**

**Ground Loss**

The ground loss term is:

Where A is the field attenuation due to ground effects:

Now for most ground and large radial distances A can be approximated as 1 / 2 p.

**Height Gain**

G_{h} is the gain improvement due to antenna heights above the ground.

*The new Lou Lichun HF and MF propagation model [1]*

I now expand the L_{m} from the work of Lou Lichun as:

Increased Path loss due to the Presence of Buildings

**Building density losses**

**Sight losses**

_{s} is the sight parameter which is calculated by executing the following procedure along the route between the transmitter and receiver:

- When a building is located in the route increase the number of building (n
_{b}) by 1 - Measure the height of the building (h
_{b}) and measure the height of the intersect of the ray with the building (h_{l}). - Compare h
_{b}and h_{l}, if h_{b}> h_{l}, then increase the number of buildings which are not lower than the Line Of Sight intersect (n_{s}) by 1. If h_{b}< h_{l}then n_{s}is not modified. - Repeat 1 to 3 until all buildings between the transmitter and receiver have been encountered.
- Calculate r
_{s}= n_{s}/ n_{b}, unless n_{b}is zero, in which case L_{s}= 0

**Receiving environment losses**

_{e} is the environment parameter representing the environment around the receiving antenna. This is a relative value that has been determined by empirical placement of antennas in various environments. It assumes that the transmitting antennas is well placed.

Suitable L_{e} values can be chosen from the following tables:

**For MF**

**For HF**

_{h} because he found that it depends on distance and the frequency, he states the G_{h} factor as:

_{p} and G_{h} terms have been expanded to form a new propagation model which Luo Lichun states helps to describe propagation in an Urban environment. He has also stated that he hopes to verify the model for distances greater than 40km. At any rate, his work represents an attempt to quantify the effects of nearby buildings (and possibly trees) on antennas. He assumes that the buildings are composed of re-enforced concrete and that they shield and scatter the RF energy.

Originally posted on the AntennaX Online Magazine by Ralph Holland, VK1BRH

*Last Updated : 27th May 2024*

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