The MeteoFax32 modem is the main factor in the quality of decoding of MeteoFax32. This modem was designed to obtain a quality of decoding even under difficult conditions of reception. This modem provides filtering and signal conversion with optimal performance even with handheld receiver. No software performing a conversion by the sound card of th computer has the required sensitivity as soon as you move away from transmitters for example during an Atlantic crossing by the area of trade winds. Only an external modem provides global coverage at sea. The control panel of the modem :

The modem :

This is achieved through:

• The use of a bandpass filter performance especially designed for signals radiofacsimile signals.

• Galvanic isolation isolates the receiver from the computer and the electric network of the vessel generating electrical interference harmful to the receptors if sensitive to interferences such as small portable receivers..

• A conversion device using a phase locked loop with large input dynamic and perfect linearity even away from either side of the working band and an Analog / Digital converter precise and stable controlled by a microprocessor which performs a first digital filtering

• An efficient filtering of power supply circuits.

• An output stage to the standard multiplexed RS 232.

This modem must be connected:

• A computer with a serial port or USB (via adapter). The program automatically detects the modem connected to a serial port or USB port.

• At a headphone or external speaker jack of the receiver.

• At a power supply 12 V. (10 to 16 V Consumption 40 mA.)

The modem is equipped with an output (jack 3.5 mm.) to collect the available signal after the band pass filter. Using a jack / jack cord between this output and microphone or line input of the sound card, it is possible to perform the monitoring of the signal with the computer either auditory or visually through the use of a analyzer or oscilloscope program as OscilloSpectroXPro. A version of this program is available on the CD-Rom MeteoFax32.

The analog filtering performed prior to conversion:

The first step in processing the signal from the receiver in the modem MeteoFax32 is the analog filtering:

1. Example of a radio facsimile signal in perfect reception conditions.
2. Example of a signal received in very bad reception conditions. Signal no decodable like that.
3. The same signal taken in filter output: this signal will give a readable document.
In some extreme cases the modem MeteoFax32 will get readable documents even if the  signal is barely audible in the receiver.

NOTE:
Those 3D spectral analysis were performed using the software OscilloSpectroXpro which a version is available on the CD-Rom MeteoFax32