Specifications

CHAPTER 9
FACSIMILE AND SSTV OPERATION
9.1 Overview
While facsimile and SSTV are not digital modes, the personal computer
coupled with a high resolution monitor makes an excellent display for
these images. The PK-900 contains modems that can receive FM
facsimile signals as well amateur Slow Scan Television (SSTV).
The PK-900 filters and digitizes the received audio signal for
processing by software running on your personal computer. Therefore
this chapter only provides an overview of FAX and SSTV operation.
The program used to display FAX and SSTV should provide operating
instructions and detailed information about the modes it supports.
Note: The Analog mode is intended to replace the old black & white
FAX mode originally developed for the PK-232. As of October 1992,
there is no display software yet available for SSTV. Gray scale FAX
is supported by the AEA FAX program.
The black & white FAX mode is retained only to support the PK-FAX and
MACRATT with FAX programs while new display software is developed.
9.1.1 Facsimile
Facsimile is the term used to describe the transmission of black &
white images. There are several different Facsimile standards in use.
Over the telephone, either "Group-2" or "Group-3" transmission
standards are used. Sending facsimile by radio has some special
problems so different and incompatible transmission methods are used.
There are two basic types of facsimile signals transmitted over radio.
Frequency Modulated (FM) facsimile is often found in the HF Short
Wave bands, while an Amplitude Modulated (APT) system is used by
satellites in the VHF and Microwave bands.
Weather Facsimile (FM WEFAX) is transmitted throughout the Short-
Wave spectrum, primarily to provide information to ships at sea.
Typical stations you may find broadcast maps with weather conditions
and satellite photographs showing cloud cover over a large area.
Not only weather information is transmitted, but also news
photographs from the wire services (see the frequency list below).
With FM facsimile, the picture information is modulated in an audio
tone between 1,500 Hz (Black) and 2,300 Hz (White). In between
these two frequencies are shades of gray. The PK-900's analog modem
receives these signals and provides an output on pin 6 of the serial
connector when Modem 8 is selected.
The PK-900 does not have a demodulator capable of receiving the
satellite amplitude modulated (APT) mode, however an AM to FM
converter is available from:
Overview Systems or call: Tim Heffield, N4IFP
P.O. Box 130014 305 748-8315
Sunrise FL 33313
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