Japan Radio Co. JAX-9B, Инструкция по эксплуатации, Страница: 109 / 118

Appendix
95
For reception of clear facsimile images
It often happens that facsimile images are blurred, disturbed or broken during reception. You may think
that your facsimile unit becomes defective or has the worse reception sensitivity. Before thinking so, let
us study the nature of wave propagation.
The short-waves are all transferred long distance by reflections on the ionosphere that surrounds the earth.
The ability of reflection of the ionosphere varies hourly, in seasons, and other surrounding conditions.
Therefore the magnitude of radio waves that you receive varies continually. This is why your facsimile
pictures are not clear. The short-wave propagation is also dependent upon the frequencies of the short
waves. Some frequencies are reflected worse but other frequencies are reflected better.
To use this characteristics, the facsimile broadcasting stations use some frequencies (in the range of 2 to
25 MHz) to broadcast identical broadcasting data. You can select any of the frequencies for optimum
reception.
Radio wave troubles in the short-wave band may be caused by multi-path echo, fading, and interference.
To receive clear facsimile pictures, it is recommended to select a frequency that is not interfered instead
of selecting a strong frequency. The Automatic Frequency Selection function of JAX-9B automatically
selects a strong frequency but this is not good enough for clear and optimum picture reception.
Therefore, you have to select a frequency for optimum reception according to the propagation conditions
that will be varied in 1) daily (morning, daytime, night), 2) seasonally (spring, summer, autumn, and
winter), and 3) distance from the station.
Appendix Figures 4 to 10 show some interfered reception samples.