RECEIVING SYSTEM ASSESSMENT @ 1.8 MHz
In this and in the following posts we shall use the data and information shown here:viewtopic.php?f=5&t=3685
to assess the noise performance in HF of an RSP receiver system equipped with the already described L=135 m Beverage antenna. Noise Floor measurements have been performed daily over two weeks and data has been classified according to Table 3 of the cited reference and also downloaded below. Received Noise Floor data has been corrected to take antenna gain/loss under consideration, as follows.
Wavelength Wl @ 1.8 MHz: Wl = 300/1.8 = 166 m
Ratio L/Wl: R = 135/166 = 0.81
From "Beverage Antenna gain Vs. wavelength", Figure 1 in the cited reference: G = -6.5 dB referred to the isotropic. This loss is due to the fact that the antenna is too short when considering a wavelength of 166 m.
Balun insertion loss is 0.8 dB. Total loss is 7.3 dB.
Therefore the Noise Floor measurements taken with this antenna show a noise level of 7.3 dB less than
the level we should have obtained if the measurement had been taken with an isotropic antenna. To compare the measurement with data and criteria of Table 3, we must correct by adding
7.3 dB to it.
The graph shown below shows the raw measurements in ligt blue and the corrected measurement in red, compared to the noise leve ranges of "Rural" and "Quiet Rural". The Rural decile range extends for +/-3.5 dB, while the Quiet Rural range extends for +/- 3 dB. By inspecting the graph, it is evident that the antenna is too short at this frequency: in fact in several days the measured
noise is notably below the lowest threshold of the Quiet Rural range. The real situation is then shown after the correction.
The noise peaks shown 22/10 to 25/10 and 28/10 to 29/10 have been caused by electrical activity due to stormy weather, which has a very strong influence at this frequency. In general, in average weather conditions, we can classify the receiving system under examination as located in a Quiet Rural situation, therefore little or nothing can be done to improve the receiving system background noise.