High Frequency Radio Facsimile

摘要

The purpose of this project was to continue the development of a standard forgray scale image transmission using High Frequency (HF) radio links. The amateur radio community is presently using a de facto standard to transmit facsimile images using HF radio. This defacto standard is called Fax 480 which uses an analog frequency modulation technique where black and white pixels are transmitted using sub carrier frequencies of 1500 Hz and 2300 Hz. Gray scale values are represented by subcarrier frequencies between the black and white limits. The images transmitted using this standard typically originate in microcomputers, and are often photographic (continuous tone) images as opposed to bi-level images. The 512 by 480 image size can be displayed with the 640X480VGA mode available on many personal computers, with room on the screen left over for menu options and other data. The transmission of facsimile over HF radio has been limited by the lack of an official standard. A requirement to standardize facsimile transmissions over HF radio, and has been developing this new standard through the TIA TR-29 facsimile committee. A draft standard has been prepared and balloted. This report comprises of three sections: 1-provides a brief description of the objectives; 2-technical discussion; and 3-conclusions.