Video remodulation unit enhances facsimile transmission using an amplitude-modulated 2400 Hz carrier. The unit demodulates the signal and then remodulates it, using the same carrier. By using the unit controls, modulation can be set to levels that compensate for picture in-transit degradation

Vermillion, C. H.

English

NASA Technical Reports Server

Vid 
lnp
Video 
Output 
June 1968	 Brief 68-10207 
N A S A TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Facsimile Video Enhancement Device 
The APT (automatic picture transmission) system 
on some current weather satellites is similar to domes-
tic television operation except for picture transmission 
which is in 240 rpm facsimile format. Similar, facsimile 
systems are also used by commercial wire services. In 
the case of the satellites' APT system, the video sig-
nal is amplitude-modulated on a 2400 Hz subcarrier. 
This subcarrier, containing the picture, is then trans-
mitted to the ground via the VHF transmitter. In a 
malfunctioning APT system, the modulation shifts 
from the design limits and the receiving facsimile, 
being unable to compensate for this shift, cannot 
present pictures suitable for meteorological evaluation.
To overcome this condition, a device called a video 
remodulation unit has been fabricated to demodulate 
the signal and then remodulate it, using the same 
carrier. By using the unit controls, modulation can be 
set to levels that compensate for picture in-transit 
degradation. 
The unit corrects for the black shift observed on 
the modulated waveform as transmitted. Provision for 
selecting a nonlinear transfer function enables the 
user to enhance the white or black areas. There are 4 
modes of operation. In the first mode, the internal 
circuitry is bypassed and the input signal is connected 
directly to the output connector. The second is a (cnntnued nverlenfl 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000207 2020-03-12T05:36:00+00:00Z
linear operating mode in which the unit demodulates 
the input amplitude-modulated video waveform and 
resets the black level of the envelope waveform. The 
resultant. waveform is amplified, its contrast levels 
reset and it is then applied to a modulation circuit that 
remodulates the waveform with the original 2400 Hz 
carrier frequency detected from the input waveform. 
The third and fourth modes operate essentially the 
same as the second mode, with the exception of non-
linear networks. These are switched into the feedback 
of the operational amplifier, which then amplifies the 
rebiased envelope waveform. The third mode enhances 
the black area of the picture, and the fourth the 
white area. Enhancing one area reduces contrast in 
the other. 
Notes: 
1. While this unit has been designed to enhance fac-
simile transmission using a 2400 Hz carrier, with 
modification it will improve degraded pictures on 
any standard facsimile carrier.
2. Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B68-10207 
Patent status: 
This invention is owned by NASA, and a patent

application has been filed.. Royalty-free, nonexclusive

licenses for its commercial use will be granted by

NASA. Inquiries concerning license rights should be

made to NASA, Code GP, Washington, D.C. 20546.

Source: C. H. Vermillion
(GSC-10 185) 
Brief 68-10207	 Category 01


Facsimile video enhancement device

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server