Improved phase locked loop receiver tracks and demodulates a signal whose signal-to-noise ratio may be low and whose information sidebands are close in frequency. This receiver recovers the carrier from input signals and applies it to a demodulator which recovers the sidebands

Daley, T. J.

English

NASA Technical Reports Server

January 1968	 Brief 68-10008 
NASA TECH BRIEF
	
-I& 
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. 
Improved Phase Locked Loop Receiver 
An improved phase locked loop receiver has been 
designed to track and demodulate a signal whose 
signal-to-noise ratio may be very low and whose infor-
mation sidebands are close to each other in frequency. 
When the sideband frequency approximates 10 percent 
or less of the carrier frequency, conventional methods 
for recovering the carrier would result in the loss of 
the information in the sideband. 
In the improved receiver, a phase locked loop 
recovers the carrier from the received input signals 
and applies it together with these input signals to a 
demodulator which recovers the sidebands. The phase 
locked loop contains a variable frequency oscillator 
(VFO) and associated circuits for generating a signal 
that is of the same frequency as the carrier. The loop 
also contains a phase detector that generates an error 
signal for controlling the frequency and phase of the 
VFO signal so that it is coherent with the received 
carrier signal. The loop includes circuitry for applying 
control and reference signals to the phase detector 
on the basis of which the error signals can be gen-
erated. A frequency standard provides the reference 
signals. The control circuitry includes first and second 
mixers and first and second bandpass litters, each 
having a passband sufficient to pass the expected 
(Doppler) frequency shift and matched phase 
response characteristics. The recovered carrier and the 
reference signals are applied to the second mixer and 
passed through the second filter to the first mixer. 
The input signals are passed through the first filter 
to the first mixer. The output of the first mixer, at the
same frequency as the reference signal, is applied as 
the control signal to the phase detector. By generating 
the control signals in this manner, the loop excludes 
noise and does not interfere with the sidebands while 
tracking the (Doppler) variation in carrier frequency. 
The carrier is recovered, even though its amplitude 
may be well below the ambient noise level. 
Notes: 
I. Although the circuitry was especially designed for 
tracking rf signals transmitted from spacecraft, it 
should be useful in systems requiring signals that 
are phase coherent with an input carrier, as in 
signal analyzers. 
2. Inquiries concerning this receiver may be di-
rected to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland 20771 
Reference: B68-10008 
Patent status: 
Title to this invention has been waived under the 
provisions of the National Aeronautics and Space Act 
[42 U.S.C. 2457 (f)i to General Dynamics/ Electronics, 
1400 North Goodman Street, Post Office Box 226, 
Rochester, New York 14601.
Source: T. J. Daley
of General Dynamics/ Electronics
under contract to
Goddard Space Flight Center 
(GSC-0956 I) 
Category 01 
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=19680000008 2020-03-12T05:43:42+00:00Z


Improved phase locked loop receiver

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