Circuit, placed in the signal path of a closed-loop receiver to modulate telemetered data in the 10-MHz spectrum, improves signal-to-noise ratio by 3 db in a communication receiver. The switch enables bandwidth reduction which reduces noise overload on the following stages, giving the system greater dynamic range

Crow, R. B.

English

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October 1970	 Brief 70-10393 
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Signal Phase Switches Offer Greater Dynamic Range 
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Use of signal-phase switch (see fig.) in a commu-
nication receiver improves the signal-to-noise (SN) 
ratio by 3 db. The switch is a novel circuit placed in 
the signal path of a closed-loop receiver to modulate 
telemetered data in the 10-MHz spectrum. This novel 
system. includes meansfordemodulation:of the telemL 
etered signals when the phase switch is driven by 
a video signal, the spectrum of which corresponds to 
that of the original modulating signal. This causes 
the output of the signal-phase switch to be an unmod-
ulated carrier when the local model of the modulator 
is locked to the input signal. This carrier signal can 
now be narrow-banded and thus remove the added 
noise caused by the i.f. "image." The switch operates 
with considerable stability and linearity over power 
levels up.
 to 3 dbm, with minimum carrier suppression 
of 50 db below unmodulated carriers. 
Originally developed for telemetry from space, the 
system is applicable to terrestrial radio-communi-
cation systems in which phase-locking techniques are 
(continued overleaf) S. 
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Aeronautics and Space Administration. Neither the United States 	 . information contained in this document, or warrants that such use 
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required for demodulation of telemetered or other 
data signals with great fidelity; it can be applied to any 
scheme having binary modulation, to measure cor-
relation of modulation with local code. The switch 
can be used in a commercial receiver to reduce the 
effect of image-noise folding. 
With the binary-modulator scheme just described, 
the signal-phase switch can be used in military re-
ceivers to reduce the effect of image-noise folding. 
Because thus far the equipment has been developed for 
digital modulation, secure military communications, 
using pseudorandom codes, seem to provide an ex-
cellent application for signal-phase switches. 
Thus the signal-phase switch has two advantages: 
(1) it enables reduction of subsequent bandwidth and 
so improves the SN ratio by 3 db by rejection of image 
noise; and (2) by this reduction of bandwidth the 
noise overload on the following stages is reduced, so 
that the system has a greater dynamic range.
Note: 
The following documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
Reference: NASA-CR-90 199 (N68-11006), 
Development of 10-MHz Phase Switches 
Patent status: 
No patent action is contemplated by NASA. 
Source: R.B. Crow of 
Caltech/JPL 
under contract to 
NASA Pasadena Office 
(NPO- 10709) 
Brief 70-10393	 Category 01


Signal phase switches offer greater dynamic range

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