Threshold extension device connected between demodulator output and filter output minimizes clicking noise. Device consists of click-eliminating signal transfer channel with follow-and-hold circuit and detector for sensing click impulses. Final output consists of signal plus low level noise without high amplitude impulses

Conrad, W. M.

Loch, F. J.

English

NASA Technical Reports Server

May 1971	 Brief 71-10091 
NASA TECH BRIEF 
Manned 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 subscription 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. 
Electronic Device Increases Threshold Sensitivity and Removes Noise

from FM Communications Receiver 
The problem: 
One factor substantially affecting the performance 
of a frequency-modulation communication system 
signal is the operation of the demodulator in the 
receiver. As the received, signal becomes weaker, a
filter is held at the last previous non-click value 
during the occurrence of the click impulse. 
How it's done: 
The FM demodulator output, consisting of the 
signal and the noise, is split into two separate 
1 FM Demodulator Threshold Extension Device 
Channel A 
 Demodulator	 Cha nnel B
	
Impulse "Click" Noise 
Detector 
Gating Pulses —b- 
i
Gated Amp lifie 
and Modulation
Iry :em Circw 
threshold point is reached below which the de-
modulator begins to introduce high-amplitude elec-
trical noise --click" noise at a greater rate. In 
addition, the form of the "click" noise is of a much 
noticeable and objectionable nature. 
The solution: 
A threshold extension device connected between 
the output of the demodulator and the output 
filter minimizes "click" noise. The device consists 
of a click-eliminating signal transfer channel with a 
follow-and-hold circuit and a detector for sensing 
the click impulses. A gated output from an ampli-
fier switches the follow-and-hold circuit to the 
hold condition, whereby the signal to the output
Low Pass 
Filter
Output 
Figure 1. 
channels (see Figure 1). The first channel (A) is 
fed to a series of impulse noise detection circuits 
which detect the presence of high-amplitude impulse 
noise ­,he primary contributor to the degraded 
performance of the FM system. Channel B (iden-
tical to channel A except for a preset time delay) 
is applied to the gated amplifier. The positive gat-
ing pulses from the noise detection circuits turn off 
channel B whenever a noise impulse occurs. This 
electronic action creates a "hole" in the channel 
(continued overleaf) 
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	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately ownedrights.
https://ntrs.nasa.gov/search.jsp?R=19710000090 2020-03-17T02:22:09+00:00Z
. 
FM	 I Click 
Receiver	 Noise 
I Eliminator 
Figure 2. 
B output which is smoothed over by additional cir-
cuitry. The output of the gating amplifier is fed to 
a low-pass filter for additional smoothing of the 
output modulation during the turn-off time. The 
apparent effectiveness of the threshold extension 
device is shown by the waveforms in Figure 2. The 
final output consists of signal plus low-level noise 
without the high amplitude impulses normally 
present. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Manned Spacecraft Center, Code JM7 
Houston, Texas 77058 
Reference: TSP7I-10091
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: 
Patent Counsel 
Mail Code AM 
Manned Spacecraft Center 
Houston, Texas 77058
Source: Frank J. Loch of

Manned Spacecraft Center, and

William M. Conrad of

Philco-Ford Corp.

under contract to

Manned Spacecraft Center
(MSC-12 165)
. 
Brief 71- 1009 1
	 Category 02


Electronic device increases threshold sensitivity and removes noise from FM communications receiver

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