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Патент USA US2407865

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Sept. 17, 1946.
-
M. ZIEGLER
5
2,407,353
RECEPTION OF FREQUENCY MODULATED WAVES
Filed April 12,‘ 1943
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MARC ZIEGLER.
INVENTOR.
,1
BY
',’
I91’
'
.
Y‘ ATTORNEY
Patented Sept. 17,‘ 1946
2,407,863
UNITEDSTATES PATENT ornca
. ‘ RECEPTION 0F FREQUENCY MODULATED
.
WAVES
‘
Marc Ziegler, Buenos Aires, Argentina, assignor
‘ to Hartford National Bank, and Trust Company,
‘Hartford, Conn., as trustee
-
'
I
" Application April 12, 194.3,‘v ‘Serial No. 482,785‘
I
,
4 Claims.
((1250-20)
1
, ‘The present invention is, concerned withYthe
reception of frequency,‘ modulated waves and
more particularly with the maintenance in prop
erly tuned condition of frequency modulatedre
:
2
.
As a matter‘ of fact, in‘ communication practice,
temperature‘ variations as large as 60° C. maybe
commonly expected, so that the same require
. ment of‘intermediate ‘frequency. stability would
ceivers, and with the prevention of the reception 5‘ lead to‘the excessive ‘requirement of 2X10“? per
' of unwanted signals.
degree C. when no thermostatic arrangement is
In the practice of reception of radio signals at
?xed frequency,v as for example frequency modu-
usedL-
‘
l
l
‘
r
j
‘-
" ' '
‘
All these drawbacks are not presentfor'th'e de
lation-communicationreceivers;and also amplié _ signs‘of' the second categorylinwhich theidee
tude modulation communication receivers, which 10 ‘sired frequency adjustment is obtained‘ by‘v'autoé
have to stay tunedto the frequency‘llof the signal
maticfrequency control commanded: by theVi'nl.
to ‘be received under ‘all circumstances, without
coming signal. ‘ Forexample, reference maybe
the necessity of ‘any readjustment, two different
made t'o‘my copending United States'Patent ap
types of designs have been proposed and are beins usedi
‘
.
,
plications Serial Nof464§380 ?led November‘ 3;
15 1942 and Serial No. 1478,705,'?1ed March‘lOI, I943
In the ?rst category, the correct frequency adjustment is guaranteed only byth‘e‘stability of
the selective circuits used and therefore, in the
places where the circuit frequency hasan impor;
where a method of automatic ‘frequency stabilie
zation is described together with'its application
to the reception of frequencyv modulated waves.
The automatic frequency control action can be
tant influence on the correct adjustment of the 20 made very e?e'ctiva'and can correct with great
receiver, the common L. C. circuit has been reaccuracy all possible deviations of the tuning‘ of
placed by a quartz crystal. Typical ‘representathe'receiver.‘ ‘ It has been‘ explained‘in. said ?rst
tives of frequency modulationreceivers using this
application, ‘that the‘ deviations of a local oscil
system usually contain two crystal o_scillators,,one
‘later from a desired frequency can‘be made prac
at higher frequency for the ?rst frequency chang; 25 tically as small, as "desired and the intermediate
er stage and a second one‘ at a lower frequency
for the second frequencychanger stage. i In that
way, a constancy of the frequency‘adjustment is
cbtained which‘ is just equal to that of the crystal
used.
I
d
g
'
,
l
frequency signal in a‘frequency modulation re
'ceiver of that type will easily be maintainedwithi
in a. few hundred cycles equal to the correct‘ ‘fre
quency, even when ‘the frequencydof the local
"30 oscillator shifts away a frequenc'y'valuewhichis
A‘real drawback of this system,,however, is that
hundreds of times as large; as for ‘instance 100'kc.
the frequency of the’ crystals ‘cannot be changed
‘ “ In ‘that‘case‘no‘ crystal is necessary, which is
‘during 0‘ eration‘. Therefore, thefrequencypre‘an important advantage, but the drawbacks" of
'cision required‘ for these crystals‘, especially'the
crystal control receivers of ‘the ?rst category'are
crystal of higher frequency is rather high in or- ‘31,-, replaced in‘ common receivers of the automatic
der to insure that a receiver of that type is really
‘frequency control type‘ by another inconvenience.
adjusted within narrow limits to'the ?xed fre-
The effective frequency control, of course'holds
quency of the transmission to be received.
only as long as the desired'signal is present,‘ and
‘
In frequency‘ modulated. reception ‘especially
in the absence of this signal the ‘frequency ad
accurate tuning is very important; ?rst; because ‘40 ‘justment which is no‘longer controlled-may shift
generally the comparative immunity of frequency
outside‘ the range of‘regulation, so that the auto:
modulation reception from impulsive interference
matic frequency Control Cannot Operate-‘When the
is dependent on ‘that accurate tuning‘and secsignal .comes in'.. In the absence of the desired
ondly because a slight detuning of the‘ receiver
. ‘s'ignal,"the automatic frequency COHtI‘OI may
may lead to unacceptable distortion owing to the 1'45 :moreo'ver'be made operative by anotherundesired
fact that at-maximum‘ frequency excursion the
signaLxth‘e receiver then adjusting itself to that
instantaneous frequency may run beyond the
undesired signal. ‘In both cases, the desired con
linear part of the discriminator characteristic.
"ditions can‘ only be restored bymanual readjust
The precision required in frequency modulated
ments, but these are of considerable inconven
communication practice‘ at 40 me. when it is de- 50 ience in many practical instances and therefore
manded that the intermediate frequency be corunacceptable in the speci?cation of a communi
rect to within 0.5 kc. is not le‘ss‘tha‘n 1.25><10—5
cation receiver.
I
‘
which‘ is a requirement making the crystal rather
I now have‘ found that‘this ‘drawback of the
expensive. For .the same reason, ‘the temperareceivers ofithe automatic frequencycontrol type
ture coe?icient of ‘the crystal must be very low. 55‘which are much superior in all other respects,
2,407,863
3
can be compensated by superposing on the de
sired signal, in some part of the receiver, a local
signal of equal frequency that will still be there
when the desired signal disappears and will take
care of keeping the automatic frequency control
arrangement in condition for adjusting the re
ceiver correctly to ‘the desired signal when the
“waiting signal.”
When the desired signal comes in, the receiver
is already adjusted on ‘the right ‘frequency so
that no manual tuning operation is necessary. In
the case of frequency modulated reception, the
presenceof the waiting signal does not cause
latter comes in again. The possible ‘frequency
differences between the emission to be received
and the local signal are readily kept Well within
the range of regulation. This local superposi
any ‘significant disturbance as long as its am
tion or substitution signal may be called “wait
ing signal.”
4
automatically on the frequency of the injected
signal. Hence, the correct adjustment is guar—
anteed also in the absence of the signal to be
received during a waiting time of any length by
Cr the injected signal, which I have therefore called
plitude is smaller than the amplitude of the sig
nalat the. ‘place. ofjinjection. This desirable
'
It is obvious that the amplitude value .of the
waiting signal must be substantially smaller than
effect is characteristic of frequency modulation
the voltage developed at the place of-injection' ' vreceivers andf-has been explained by H. Roder '
in the publication “Electronics” (May, 1937, vol.
by the transmission signal during the reception
'10, No.5, pages 22 to 25 inclusive, 60, 62 and 64) .
so as not to interfere with the desired signal ’
As pointed out- therein, a frequency modulation
during its reception.
,
.
It is very commonly required in the specifica 20 receiver is only responsive to the stronger of two
signals‘. .litirthermorewhen the amplitude of the
tionof a communication received that the re
weaker of the. two signals is less than one-half
ceiver shall be made insensitive to ‘all signals
the amplitude of the stronger signal, the dis
below a certain level. In or'derto ful?ll this
turbing
phase shift produced (and hence the dis
requirement, all kinds of complicated silencer
turbing
equivalent frequency modulation pro
or squelch arrangements have, been ‘designed for 25
duced) is never more than about one-two hun
cutting down the ampli?cation of, some part of
dredths (1/200) of the legitimate phase shift-equiv
the receiver so long as the incoming signal has
alent to the permissible degreeof frequency mode
not reached a certain minimum value.- This
ulation of the signal. Such. a small disturbance
minimum valuefgenerally is adjustable in order
cannotrproduce a signi?cant interference effect.
to :make? the, receiver adaptable :to' different rrcon
30
ditions of reception. _ The ,adyantage of such a
silencer or squelch arrangement is that, when
the desired signal isrnotpresent, noises from
other; and less. strong‘ signals, static interferences
‘and internalspontaneous _fluctuations are not ‘ '
reproduced and the receiver is completely quiet.
I have‘ now found.- ‘that a very convenient
squelch action can be provided by the above men
tioned waiting isignal. "As a matter of fact, this
waiting signal can ‘be made‘ adjustable to any 1
valuelso' vthat any squelch level may be obtained.
Withmy invention. I therefore solve two prob-,
lems at the same time: 'First,'-that of'improv-r.
In the case of an amplitude modulated receiver,
the waiting signal will produce with ‘the desired
signal a beat frequency’ signal which may be
audible and therefore unacceptable. ; The only
solution in that case would be to switchloif the
waiting signal generated as soon as necessary.
< The above mentioned property of the frequency
modulated receiver can be made use of for ob
taining an adjustable silencer by providing the
signal oscillator of Fig. 1., with a convenient ad
justable attenuator.
As a matter of fact if we
inject a’ non-modulated signal of, for example,
50 microvolts in the antenna, the [receiver will
respond only to signals larger than said value
ingthe security of operating conditions ofya fre
and if no signals are present larger than 25
quencymodulated receiver of theiautomatic fre- i‘ 'microvolts, the receiver will be, perfectly quiet.
quencytcontrol type and" second that of provid-_
If used for that purpose, the injected signal
ing a' very ‘simple and very effective squelch
may therefore be called a squelch signal, as it
device.v
~.
"
3
I
,,
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have also foundsthat' it is not unavoidably
necessary to‘ obtain the waiting andsquelch sig 50
nal from a special local oscillator, which would
me'arita complication of the design, but that it
‘can ‘be derived from one of the existing local
replaces the squelch arrangements known in the
art.
,.
7
‘
>
holds for any level above the normal
lower working limits ofrthe receiver which gen;
erally, for frequency modulated communication
receivers wherein a silencer
needed, is very
‘low,
that
is
lower
than
1
microvolt.
This and other details and features of my
.As a matter of fact,'the waiting and squelch
invention will ‘be’madeolear in ‘the description
signal does, not nee'dgto be injected in the an
‘of the ?gures, wherein
tenna of the receiver but at any point; before the
Fig. 1 represents a block diagram of a fre
mixer.
Thevalue of the signal injected then, of
quency modulation receiver of the automatic
frequency ‘control’ type with a separate crystal 60 course,v must be increased adequately.
‘The disadvantage ofan arrangement such‘as
' oscillator providing the waiting and squelch sig
that
ofv Fig. l is that it requires ‘in addition to a
nal required.‘
1
‘
g
c
;
i
w
normal receiver a complete oscillator plus attenm
' "Fig; 2 ‘representsTschematically‘a basic em
‘ator whiohmakesithe feature a rather expensive
‘bodinient vof ' a receiver wherein an" adjustable
.2 however, the effects described have
_waitingandsquelchwsignal vis obtained from a 65 one: ;
oscillators of the receiver. -
-
1
local quartzi crystal oscillator .of the receiver.
‘In Figure l, ‘S is a well‘shielded signal gener
atonof frequency substantially equal to that of
'the'signa'l to ‘be received, and of a constancy bet
ter than that of the local oscillators used in the
I receiver R, as for example a crystal oscillator.
This generator provides at the‘ input of the
receiver'a signal of smaller amplitude thanthe
signal to be received but large enough to make
the receiver operate correctly and adjust itself
been fully obtained withoutthe addition of‘a
separate. oscillator. ‘The waiting signal is prof '
videdloy one off the local‘ oscillators normally
present in the receiver, thefrequency of said local
oscillator being kept automatically at the cor‘
rect value by stabilization from the other local
oscillator which itself is quartz; stabilized.
This receiver'has therefore all the stabilityof
a receiver with a, local crystal‘ oscillatorand the
consequentguarantee of ‘receiving the communi
cation when it comes in, and all the automatic
' This may
‘M of frequency
‘
present some difficulties, but-these
di?iculties can be solved conveniently by using
the existing technique of standard signal genera
adjustability to the incoming signal of a classical
receiver of the automatic frequency control type
with consequent advantages with regard to se
lectivity and absence‘of distortion.
In the example given in Fig. 2 the signal fre
quency is is. After one stage of radio frequency
ampli?cation It the ?rst mixer I2 is passed
through, which operates with a quartz oscillator
tors and the like.
tative since the choice of the circuit maydepend
on particular circumstances which do not effect
in any way the fundamental nature of the 'in
'
i
'
It must also be understood‘that'the present
invention may be applied either to frequency
15 modulated receivers of classical types or to those
incorporating automatic frequency stabilization
to obtain a ?rst intermediate frequency
Z5
77’+f..
using frequency counters, especially inductance
The second mixer 16 operates with an oscillator
type frequency counters, or those using excursion
w
shrinkage and the like, as described in my 00-,
[l
pending United States patent-applications Serial
Nos. 464,380, ?led November 3, 1943, 477,990 ?led
20
n
‘
readily devised by those skilled in the art, to give
'
‘
'
the same results on the same principles. The
circuit indicated is notto be considered as limi
vention.
[8 at frequency
i
Evidently, many other arrangements can be
,
March 3, 1943, 478,705 ?led March 10,1943 and
so as to get a second intermediate frequency f1.
451,186, ?led‘ July_16,
The waiting and squelch signal is obtained as
the nth harmonic of the second local oscillator
18. This harmonic, as is well known, always
exists in practice, in the anode circuit of the os
cillator tube and may be obtained without ‘fur
ther equipment. The intensity of the harmonic
wave is adjustable by means of the attenuator
28. The second intermediate frequency wave is
I claim:
‘
1942. ‘ ‘
‘
‘
'
‘
>
a
1. A superheterodyne receiver for frequency
modulated waves comprising an input channel
for receiving a signal wave, a first mixer stage '
coupled to said channel to receive said signal
wave therefrom, a wave source coupled to said
mixer stage for producing a ?rst intermediate
frequency wave, a second mixer ‘stage coupled
to said ?rst mixer stage,_ a controllable frequency
oscillator generating a fundamental ‘frequency
wave coupled to the saidsecond mixer stage for
amplified by the intermediate frequency ampli
?er 22 and applied to the discriminator 24 which
in turn controls the reactance tube 26 and ener
gizes an audio frequency ampli?er 28 and a loud
_ producing an intermediate frequency Wave hav
speaker 30 in known manner. The discrimina
ing‘a predetermined frequency value, an inter
tor is adjusted so as to give a control voltage
mediate frequencyampli?er coupled to the said
which is 'zero in value when'the frequency ap
second mixer stage‘, a frequency-responsive de
plied at its input is equal to the nominal inter
tector coupled to the intermediate frequency am
mediate frequency ii. The Ifrequency of the sec
ond localloscillator I8 is automatically controlled 40 pli?er for producing a control voltage propor
tional to the average deviation of the said sec
by means of the reactance tube 26 on thegrid
ond intermediate frequency wave from the said
of which the output of the discriminator is ap
predetermined value, means responsive to the
plied.
said control voltage for varyingthe frequency of
It will readily be understood that the oscilla
tor ill will be adjusted automatically at such a > the oscillator in a sense to reduce the deviation
of said second intermediate frequency wave from
frequency that the output of the discriminator
the predetermined value to substantially zero,
will be as nearly possible zero, that is when the
means to inject into said ?rst mixer a wave hav
intermediate frequency is as nearly as possible
ing a frequency'which is substantially equal to
equal to the predetermined value ii for which the
discriminator is adjusted, .so that the controlled - frequency of the Wave applied from the input
channel and which bears a harmonic relation
oscillator frequency will be practically
ship to the frequency of the said fundamental
f5
.
-
wave to produce in the intermediate frequency
ampli?er an intermediate frequency wave sub
stantially the same frequency as the frequency
of the intermediate frequency Wave and at the
7L
and its nth harmonic will have substantially the
frequency of the signal to be received. The
waiting and squelch signal therefore works sim
ply as described above for Fig. 1.
output of the‘ detector 'a control'voltage substan
tially equal to the ‘control voltage derived from
’
said second intremediate frequency wave‘result
ing from the signal Wave, and means to vary the
For n any value may be chosen larger than 2
and smaller than‘ a higher limit determined by
practical considerations. For lower values of n
(3 or 4) a good signal-to-image relation is ob
tained; for higher values of n a better ampli
?cation of the first mixer stage may be expected
as the ?rst intermediate frequency is lower but
the signal~to-image relation is poorer and it may
intensity of the said injected wave."
modulated Waves comprising an input channel for
‘a signal wave, a ?rst mixer stage coupled to the
input channel to receive said signal wave there-,
from, a wave source coupled to said mixer stage
for producing a frequency modulated interme-'
diate frequency wave, a second mixer stage cou
become difficult to obtain enough squelch signal
amplitude of the desired frequency. For a sig
nal frequency of 40 mc. the value of n=4 seems
to be convenient.
,
'
' ‘
2. A superheterodyne receiver for frequency
. pled to said ?rst mixer stage, a controllable fre
quency oscillator generating a fundamental fre
It must be observed that a. very careful shield
ing of the second local oscillator 18 is necessary
in order to reduce the waiting signal picked up
directly by the antenna or other parts of the re
ceiver down to the lowest limit of reception. 75
quency Wave coupled to the said second mixer
stage for producing a frequency modulated inter
mediate frequency wave having a predetermined
frequency value, an intermediate frequency am
pli?er coupled to the said second mixer stage; a i
2,407,863
‘7
frequency-responsive detector‘ coupled to the ‘in-'
terr'nediate frequency ampli?er for producing ‘a
control voltage proportional to the. average de
viation of the said second intermediate frequency
wave from the said predetermined value, means
control ‘voltage substantially equal to the control
voltagev derived from the said second frequency
modulated intermediate‘ frequency wave, and
means to vary the intensity of the said injected
Wave to thereby adjust then-intensity of the said
responsive to the said control voltage for varying
third intermediate frequency wave to a value
theifrequency of the oscillator in a sense to re
greater than a predetermined value and less than
the intensity of the said second frequency modu
duce the average deviation of the said interme
diate ‘frequency wave from the predetermined
value to substantially zero, means to inject into
said ?rst mixer a wave having a frequency which
lated'intermediate frequency ‘wave. r»
.'
7-:
-'
4. A superheterodyne receiver for :frequency
modulated waves comprising an input channel
for a frequency-modulated signal Wave, a ?rst
is substantially equal to the frequency of the
wave applied ‘from- the input channel and which
bears a harmonic relationship to the frequency
of the said fundamental-wave to produce in the
intermediate frequency ampli?er an intremediate
frequency wave having a frequency substantially
mixer stage coupled to‘ the input channel to re
ceive said signal wave therefrom, va stable fre-‘
quency oscillator coupled to the mixer stage, the
frequency of the oscillator being equal to
the same as the frequency of the said second fre
quency modulated intermediate frequency wave
and at the ‘output of the detector a control volt 20 where fs is the central frequency of the signal
age substantially equal to the control voltage
wave received, 11 is any number greater than
2 and fl is a predetermined intermediate fre
derived from the said second frequency ‘modulated
intermediate frequency Wave, and means to ad
quency,v a second mixer ‘st-age coupled to said
just the intensity of the said injected wave to
?rstvmixer stage, ‘a controllable frequencyoscil
thereby adjust the intensity of the said third 25 lator'generating a fundamental wave nominally
intermediate frequency wave to an intensity
equal to the, frequency of the received signal Wave
divided by n and harmonics of ‘said fundamental
' greater than a predetermined value and less than
the intensity'of the said second frequency modu
frequency coupled to said second mixer stage for
lated. intermediate frequency'wave.
3.7A superheterodyne receiver for frequency
modulated waves comprising an input channel
producing an intermediate frequency wave hav
30
for a frequency modulated signal wave, a ?rst
mixer stage coupled to the input channel to re
ing a frequency nominally’ equal to if, an inter
mediate frequency ampli?er coupled to said sec
ond mixer, a frequency-responsive detector cou
pled to the intermediate frequency ampli?er for
modulated intermediate frequency Wave, a‘sec
0nd mixer stage coupled to said ?rst mixer stage,
producing a control voltage proportional to the
deviation of the intermediate frequency wave from
the value if, means responsive to the said'con
trol voltage for varying the fundamental and
a controllable frequency oscillator generating a
harmonic frequencies of the controllable oscil
ceive said signal wave therefrom, a wave source
coupled to said mixer for producing a frequency _
fundamental Wave ‘and harmonics thereof cou
lator in a sense to reduce the average deviation
pled to the said second mixer stage for producing
a frequency modulated intermediate frequency
of the said second intermediate frequency'wave
Wave having a predetermined intermediate fre
to inject a harmonic of said controllable oscil
lator ‘substantially equal to the frequency is into
the first of said mixers to produce in the inter
quency value; an intermediate frequency ampli
?er coupled to’the said second mixer stage, a
frequency-responsive detector coupled to-the in
termediatefrequency' ampli?er for producing a
control voltage proportional to the average de
viation 0f the said second intermediate frequency
wave from the said predetermined value, means
responsive to theisaid control voltagefor varying
the fundamental and harmonic frequencies of the
oscillator in a sense to reduce the average, de
viaticn of the said second intermediate frequency
' wave from the predetermined value to substan
tially zero, means to inject a harmonic wave
from the oscillator into the said ?rst mixer to ‘
produce in the intermediate frequency ampli?er
an intermediate frequency Wave having a fre
quency substantially same as the frequency of
the said second frequency modulated intermediate
frequency waveland at the output of the detector a
from the value fr to substantially zero, means
: mediate frequency ampli?er an intermediate fre
quency wave having a frequency substantially
the same as the frequency of the "said second in
termediate frequency wave derived from the sig
nal-wave and at the output of the detector a
control‘ voltage substantially equal to the con
trol voltage derived from'the said second inter
mediate frequency wave resulting from the sig
nal wave, and means to vary the intensity of the V
injected harmonic wave to thereby adjust the
intensity ofthe said third intermediate. frequency
wave resulting from the harmonic wave to a value
greater than a predetermined value and less than
the intensity of the said second intermediate fre
quency Wave resulting from the signal‘wave,
MARC ZIEGLER; y:
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