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Патент USA US3076157

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Jan. 29, 1963
Filed Nov. 12, 1959
2 Sheets-Sheet 1
m .
Jan. 29, 1963
Filed NOV. 12, 1959
2 Sheets~$heet 2
United States PatentfO?Fice
quencies will be cited as examples" so that the under‘
Nicholas J. Re'eher, Hicksville, N.Y., assignor to Hazeltine
Patented Jan. 29,v 1963
standing' of theinvention will be‘ facilitated. The main
carrier signal may have a" frequency of the'order of 100
megacycles, and the subcarrier signal may‘ have a free}
Research, Inc;,"a*c0rporation of Illinois
FiledNov. 12, 1959, Ser. ‘No. 852,354
2 Claims. (Cl. 329-140)
quency of the order of 50 kilocycles. The maximum
frequency deviation of the subcarrier which corresponds
to the maximum‘ amplitude of the subcarrier modulating
signal may be of the'order of :10 kilocycles. The per‘
General -
This'invention' relates to apparatus for detecting the
information of a frequency-modulated subcarrier signal.
centage deviation of the subcarrier, being the’ ratio of
the maximum frequency deviation,-na'mely 20 kilocycles,
to the subcarrier frequency, namely‘ 50 kilocycles; is
The subcarrier technique is fast becoming a popular
therefore .4 which‘ is'large when compared to a‘ fre
way oftransmittin’g'a plurality of’ signals on one main
quency deviation of :75 kilocycles and’carrier frequency
carrier. With respect to FM signals, the subcarrier-tech
of 100 megacycles. The'last-two?gures are typical of
n-ique may be‘ brie?y?‘ explained as follows; The subcar-v
rier, in the order of 50 kilocycles, is frequency modu 15 present FM’ carriers and' allowable frequency‘ deviations;
Means 10 may preferably include an antenna 711 and
lated by‘v a subcarrier- modulatingsignal which contains
a conventional FM tuner 12. The'tuner‘may include the
information. The main carrier, in the order of 100 mega~
basic circuits such' as' a'wlocal oscillator, intermediate
cycles and representative of a channel frequency, is‘fre
quency modulated by both a main modulating signal, 20 _requency ampli?er, and-a detector for detecting the main
modulating signal of the main carrier. The main modu
which also contains information, and the frequency
lating signal is derived at an output terminal 13‘ and sup
niodulated subcarrier signal. Thus, two signals are trans
mitted in'one channel and on the one main carrier which
is representative of the channel frequency. Subcarrier
plied to a suitable utilizing device such as a loudspeaker
13a. Connected to the tuner is the apparatus for de
transmission is feasible since each channel has an allow 25 tecting the information of the frequency-modulated sub
carrier signal. This apparatus‘ includes, in the order
able band width which is capable of handling one or
named, a ?lter 14; means 15 including a reactancere
more‘ subcarrier‘ signals without interfering with adjacent
sponsive to the subcarrier signal for developing an am
channels or individual subcarrier signals.
plitude' modulatedjsignal, the variations‘ of’ which are in‘
At the receiving end, the main modulating signal is
separated from the subcarrier and is detected, and the 30 accordance, with frequency variations of the subcarrier
signal; and detectionmeans 16 responsive to the ampli
subcarrier modulating signal, in turn, is detected from the
tude modulated signal for-detecting the variations in am;
subcarrier. The present invention relates to a detector
plitude. Filter 14 is designed to have a pass band sub
used for detecting the subcarrier modulating signal from
the'subcarrier. Among the advantages of this detector
stantially equal to the maximum frequency deviation of
components. This, in turn, requires less power during
subcarrier frequency.v Means 15 mayinclude an‘ elec
tron-discharge valve such as pentode 17 for translating
the subcarrier signal at constant current. It should be
is that it is composed of a relatively small number of 35 the subcarrier signal and ‘centered approximately at the
operation.‘ Both these factors render the unit more prac
noted that a transistor, which is‘capable of translating
It is'an object of the present invention, therefore, to
provide new and'improved apparatus for detecting in 40 at constant current, may also be used in place of‘ the
pentode. Connected to the output of pentode 17 is a
formation of a frequency-modulated subcarrier signal.
reactance, such asind'uctor 18 responsive to the subcar
7 In accordance with a particular form of the present
rier signal. Detection‘means 16 is composed of the con;
invention, in apparatus for detecting the information'of'
ventional elements found in a basic AM detector. The
a high-frequency carrier signal having a low-frequency
subcarrier modulating signal is derived at an output ter-[
frequency~modulated subcarrier signal with a large per
minal 19 and supplied to a suitable utilizing device such
centage deviation, means for translating the subcarrier
as a loudspeaker 19a.
signal at‘constant current. The invention also includes
means, consisting of an inductance responsive to the sub
Operation of Apparatus of FIG. 1
carrier signal translated by'the current translating means
Means’ 10‘supply a‘
for developingan- amplitudeemodulated signal, the varia
tions‘ of which‘ are-in’ accordance‘ with frequency varia
tions'of the subcarrier signal and detect-ion means respon
carrier of low frequency
is frequency modulated
afrequency deviation,which-results in- a large percentage‘
sive tothe amplitude-modulated signal for detecting the
variations in amplitude.‘
For a; better understanding of- the present invention,
together with'other- and'further-objects thereof, reference
high-frequency carrier signal hav
ing ‘a frequency-modulated ,subcarrier'of ‘much lower fre-'
than the carrier. The frequency-modulated‘ sub;
deviation of the subcarrier for reasons to be‘ explained."
More particularly, the subcarrier signal, having for eX-'
ample a, frequency of the. order of- 50 kilocycles,’ is ire?
is‘ had to' the following description taken in connection
quency modulated by a subcarrier modulating" signal
with the accompanying drawings, and its scope will be
which causes a frequency deviation of about :10 kilo
pointed out in the appended claims.
Referring to the drawings:
60 cycles in the subcarrier. The carrier signal of about 100
megacycles is frequency modulated by both a main mod
FIG. 1 is a preferred embodiment of the present in
ulating signal and frequency-modulated subcarrier signal.
vention, and
The antenna 11 receives the transmitted signal and sup
FIG. 2 shows curves which will facilitate the under
plies it to the tuner 12. The tuner 12 derives the main
standing of the invention.
65 modulating signal along with the subcarrier signal in a
Description of Apparatus of FIG. 1
conventional manner. The main modulating signal ap
pears at an output terminal 13 and may be represented
FIG. 1 shows apparatus for detecting the information
of a frequency-modulated subcarrier signal. Means 10
by curve A of FIG. 2. The subcarrier signal, which may
be represented by curve B, is supplied to ?lter 14. Curve
supply a high-frequency carrier signal having a frequency
modulated subcarrier signal of much lower frequency 70 B shows that the frequency-modulated subcarrier has as
than the carrier and having a large percentage devia
its envelope the main modulating sign-a1. Filter 14, hav
ing a pass band substantially equal to the maximum fre
tion. While the invention is not to be limited to any
quency deviation of the subcarrier signal and centered
speci?c frequency or range of frequencies, typical fre
approximately at the subcarrier frequency, ?lters Gulf-imam
Capacitor 22 ____________ __inicromicrofarads__ 350
Capacitor 23 ________________________ __do____ 750
Capacitor 24 ________________________ __do____ 6800
Capacitor 25 ________________________ __do____ 3000
main modulating signal and derives only the subcarrier
signal. This is shown in curve C. Curve C is the fre
quency-modulated signal which contains the information
of the subcarrier modulating signal. The signal rep
resented by curve C is supplied to means 15 which de
velops an amplitude-modulated signal, the variations of
which are in accordance with frequency variations of
the subcarrier signal. More particularly, if the current
Inductor 26 ___________________ __millihenries__
Inductor 27 _________________________ __do____.
Resistor 2S _______________________ __kilohms__.
Resistor 29 _________________________ __ohms__
Capacitor 30 __________________ __microfarads__
from the pentode 17 is maintained constant, the voltage
across the inductive coil 18, which varies linearly with 10 Capacitor 31 ________________________ __do____
Capacitor 32 ________________________ __do____ 0.003
the frequency of the current through the coil, varies in
Resistor 33 _______________________ __kilohms__
amplitude in accordance with variations in frequency.
Capacitor 34 ___________________ __rnicrofarad__
The amplitude-modulated signal developed across in
Subcarrier frequency _____________ __l;ilocycles_..
ductive coil 18 may be represented by curve D, the dotted
portion thereof representing the amplitude modulation.
15 subcarrier band width __________________ -_do__ :25
It will be noticed that at this point in the apparatus, the
While there has been described what is at present con
‘frequency-modulation components are still present in the
sidered to be the preferred embodiment of this invention,
it will be obvious to those skilled in the art that various
changes and modi?cations may be made therein without
signal. In effect, the developed amplitude varying signal
amplitude-modulates the frequency-modulated subcarrier.
The signal represented by curve D is supplied to the de 20 departing from the invention and it is, therefore, aimed
tection means 16 which detect the amplitude-modulated
signal or the variations in amplitude in a well-known
manner and supply it to an output terminal 19. The
detected signal, represented by curve B, is therefore the
detected information of the subcarrier signal.
It is important to note that the use of the simple in
to cover all such changes and modi?cations as fall within
the true spirit and scope of the invention.
What is claimed is:
1. In apparatus for detecting the information of a high
frequency carrier signal having a low-frequency fre
quency-modulated subcarrier signal with a large percent
age deviation: means for translating said subcarrier sig
ductor 18 is practical only because the subcarrier fre
quency is low and its relative frequency deviation large,
nal at constant current; means consisting of an inductance
thereby resulting in a large percentage deviation. This 30 responsive to said subcarrier signal translated by said
is because the ratio of voltage swing to unmodulated
current translating means for developing an amplitude
voltage would be prohibitively small and the system
modulated signal, the variations of which are in accord
would be excessively sensitive to amplitude variations of
ance with frequency variations of said subcarrier signal;
the input signal if low percentage deviation were used.
and detection means, responsive to said amplitude-modu
It is apparent from the foregoing that the apparatus
lated signal, for detecting said variations in amplitude.
may function even when two subcarriers are transmitted
2. In apparatus for detecting the information of a high
on the main carrier signal provided that appropriate sub
frequency carrier signal having a low-frequency fre
carrier frequencies and maximum frequency deviations
quency-modulated subcarrier signal having large fre
are chosen so that there will be no interference between
adjacent channels or individual subcarriers. Additional
?lters, such as the one shown clotted, having different
pass bands, may be placed in parallel with the ?lter 14.
The subcarrier to be detected may be chosen by inserting
quency deviation to subcarrier frequency ratio: means
including a ?lter circuit having a pass band conforming
to said frequency deviation for deriving the subcarrier
signal; means for translating said subcarrier signal at con
stant current; means consisting of an inductance respon
sive to said subcarrier signal translated by said current
a selector switch between the tuner and the ?lters and,
in this way, selecting a particular ?lter having a pass band 45 translating means for developing an amplitude-modulated
ignal, the variations of which are in accordance with
which corresponds to the particular subcarrier which is
It is also apparent that the apparatus for detecting the
information of a frequency-modulated subcarrier signal
frequency variations of said subcarrier signal; and detec
tion means, responsive to said amplitude-modulated sig
nal, for detecting said variations in amplitude.
may be built within the tuner 12 so as to make the tuner
and the apparatus for detecting the subcarrier one com
plete unit.
While applicant does not wish to be limited to any
particular circuit constants, the following approximate
circuit values are suitable ‘for use in the apparatus repre
sented by FIG. 1:
Pentode 17 ______________________________ ....
Diode 20 __________________ _; ___________ .._
Inductor 18 ___________________ __millihenries__
Resistor 21 ______________________ __kilohms__
Capacitor 35 _____________ __micrornicrofarads__
References Cited in the ?le of this patent
Roberts _____________ __ Feb. 17, 1942
Roberts _____________ __ Mar. 17, 1942
Albright _____________ __ June 19, 1945
Crosby ______________ __ Sept. 30, 1947
Shenk et al. __________ __ Apr. 25, 1950
Barton ______________ __ Nov. 30, 1954
Buie ________________ __ Nov. 27, 1956
Bose ________________ __ May 20, 1958
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