Reception of facsimile images
It often happens that a facsimile image is blurred, distorted or 'torn.' You may find that your fax receiver is defective or lost sensitivity. Before making such conclusions presented below examine the material on the radio waves.
Short waves are transmitted over long distances by reflection from the ionosphere surrounding the earth. The reflection of radio waves varies depending on the time of day, time of year and other factors. Therefore, the strength of incoming radio waves constantly changing. That's why your fax images are fuzzy. Passage of radio waves also depends on the frequency used. Some frequency signals reflected better, while other signals frequencies practically not recognized. Therefore, virtually all facsimile broadcast station uses several frequencies within the range of 2 to 25 MHz for transmission of identical data. You can select the optimum frequency for best reception.
Multipath propagation of short waves can cause the echo attenuation and interference.
To receive a clear facsimile image is recommended to select the frequency at which no observed signal interference. Automatic frequency selection function automatically selects the frequency at which the signal level is maximum, however, is not always successful for optimal reception of the image.
So you need to select the optimum frequency for receiving according to the conditions of passage of the signal depending on the time of day (morning, afternoon, night), season (spring, summer, autumn and winter) and distance from the station.
Fax receiver receives the fax signal from the air and converts it into an image. In the process of converting the print head starts to print an image point by point, starting from the left edge to the right fax paper, returning to the left edge of the fax paper from the right and typing a new line from left to right.These steps are repeated until, until the signal is received complete image. These movements printhead device called 'scan'.
Movement of the print head from left to right. In a conventional scan, the print head prints dots at eight 1 mm.
Scanning line density:
The number of printed lines by moving the paper 1 mm Scanning speed (SCAN): main scanning speed (scanning expressed in minute). E.g., 120 SPM, for example, means 120 scans per minute.
The proportionality coefficient (IOC):
If the document (original) sent from the weather station does not match the size of paper in the fax receiver, the original image is reduced proportionally to the size of fax paper with the length and width of the original document. This value is the coefficient of proportionality.
Record in semitones (HALF):
Using the template points of different density (roughing and fine print) provided mapping clouds in grayscale at photos from meteorological satellite.
This is the first facsimile signal broadcast transmission from the weather station. Signal indicates the beginning of fax transmission. When receiving this signal, the receiver automatically starts to receive fax broadcast signals.
The synchronization signal:
The signal which follows the start signal, and after image transfer, if the signal is successfully synchronized. The receiver uses this signal to automatically adjust the density and the scan rate. This signal is always required for the automatic reception, and receiving a manual reception programmable.
Signal following the phase signal and always passed by the end of the transmission image. The receiver uses the signal for phase matching (sync) with manual reception and forced entry.