Program studies and designs combline filters and analyzes their effectiveness in improving TV quality. Signal tracking methods are improved. Combline phase-lock loop provides significant sensitivity improvement above and below threshold

Develet, J. A., Jr.

Huang, M. Y.

Stuber, F. M.

English

NASA Technical Reports Server

May 1971	 Brief 71-10141 
NASA TECH BRIEF 
iVIaiiiied Spacecraft Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a aubscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
New Filter Technique Improves Home Television Reception 
Based upon theoretical reasoning, a program was 
undertaken to study and design combline filters 
and to analyze their effectiveness in improving TV 
signal quality. A television signal has a large portion 
of its transmitted energy at multiples of the line-
scanning frequency, with little energy in between; 
i.e., the energy spectrum is roughly analogous to the 
teeth of a comb. If a filter consisting of passbands 
and stopbands congruent with the comb shape of the 
TV signal could be constructed, the noise-filled empty 
space could be filtered out and the energy-filled 
portion passed through, with a subsequent improve-
ment in the signal-to-noise ratio (SNR). Further, 
if a combline filter were used as the filter in a 
phase-lock loop (PLL) demodulator, the effective loop-
noise bandwidth would be reduced and the threshold 
would be improved; in other words, the loop would 
operate more efficiently and the demodulator would 
produce usable signals at an input SNR several 
dB below that of a PLL demodulator without the 
filter. 
After investigating a variety of combline filter 
techniques, a PLL demodulator with the combline 
filter as the loop filter was built and analyzed. A 
16 dB threshold improvement and a 7 dB signal-
to-noise ratio improvement above threshold was 
achieved when compared with a first-order PLL 
measured for tone modulation and narrowband
additive RF noise. The expected tracking problems 
were encountered for TV. signals due to low loop 
gain requirements, but methods for improvement were 
conceived and implemented. Despite the problems 
encountered, a combline phase-lock loop provides 
significant sensitivity improvement above and below 
threshold. 
Note: 
The following documentation may be obtained 
from:
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NA SA-CR- 108506 (N70-34526), The Combline 
Filter and Phase-Lock Loop, A New Tech-
nique to Improve FM Television Reception 
Patent status: 
No patent action is contemplated by NASA. 
Source: J. A. Develet, Jr., F.M. Stuber,

and M. Yu Huang of

TRW Systems Group
under contract to

Manned Spacecraft Center

(MSC-13729) 
Category 02 
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=19710000140 2020-03-17T02:24:11+00:00Z


New filter technique improves home television reception

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