**5. ANTENNA DATA AND NOISE FLOOR EVALUATION**

The Noise Power delivered to the Receiver by a loss free antenna is equal to the flux density of the electromagnetic radiation impinging on the antenna times the antenna Effective Aperture. As will be shown in the Appendix, the Antenna Effective Aperture is nothing else than the Antenna Gain Factor G.

Table 4 provides data for several antenna types in common use in HF. We can now evaluate noise performance of a practical receiving system, leaving out only the influence of antenna elevation. The wideband Beverage antenna data cannot be tabulated because gain depends on wavelength ratio and is shown in the graph of Figure 1. Equations shown in Figure 1 can be used to calculate gain for any Beverage antenna length, different heights above ground and at any frequency. The graph is valid for average dry soil.

**Examples amended 05/10/2018**

EXAMPLE 1

A half wave dipole, operating at 14.3 MHz (20m Band) measures a noise floor of -120 dBm. Coaxial line / balun loss amounts to 1.2 dB.

From Table 4 we find r’ = -2.15 dB.

Therefore the corrected antenna nose floor Anf= -120 + 1.2 + 2.15 = -116.6 dBm

Applying the decile deviations: -113.6 > Anf > -119.6

In conclusion (Table 3) we are in a “Quiet rural” situation.

EXAMPLE 2

If the same half wave dipole, at the same frequency, exhibited an Anf of -98 dBm, it would be positioned in a “City” situation.

EXAMPLE 3

An L = 135 m Beverage antenna, at an average height of 6 m operates at 3.6 Mhz and measures an average noise floor of -104 dBm. Balun loss is negligible. The Beverage is a wideband antenna and gain depends on the ratio of length L to wavelength W.

At 3. 6 Mhz Wavelength W = 300/3.6 = 83 m.

L/W = 135/83 = 1.62

From Figure 1, r’ = -2.8 dB.

Therefore the corrected antenna nose floor Anf= - 104 + 2.8 = - 101 dBm

Applying the decile deviations: -98 > Anf > -104

In conclusion (Table 3) we are in the bottom end of the “Quiet rural” situation.

Some data in Table 4 has been taken from: "RDF METRIC"

http://www.seed-solutions.com/gregordy/ ... Metric.htm

Beverage antenna data has been derived from:

BEVERAGE ANTENNAS FOR HF COMMUNICATIONS,

DIRECTION FINDING AND OVER-THE-HORIZON RADARS

By J. Litva and B.I. Rook / Report No. 1282 /Dept. of Communications / Ottawa, August 1976