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Patented Sept. 24, 1946
Charles Malton Le Grice Eyre and John Owen
Gilderdale, London, England, assignors, by
mesne assignments, to International Standard
Electric Corporation, New York, N. Y., a cor
poration of Delaware
Application January 12, 1944, Serial No. 517,912
In Great Britain February 1, 1943
5 Claims.
(Cl. 250—20)
The present invention relates to electric ther
mionic valve modulating arrangements, and is of
particular application to superheterodyne re
arranged in a cathode follower circuit with a re
sistance in series with the cathode, means for
applying simultaneously to the control grid two
In superheterodyne receivers it is sometimes
series of input waves having different frequen
cies, means for biassing the valve in such man
desirable to couple the frequency changing stage
aperiodically to its load, and in particular to
pedance output means connected to the resist
couple it aperiodically to a load of relatively low
ance for extracting therefrom waves having a
her that it operates as a recti?er, and low im
frequency equal to the difference of the input
impedance. For example, it may be desired to
construct a receiver in which the intermediate 10 frequencies.
According to another aspect, there is provided
frequency is variable over a ‘certain frequency
a modulating or demodulating circuit compris
band, the frequency of the beating oscillator be
ing ?xed, and the output‘ of the frequency
ing a thermionic valve having a cathode, anode,
and control grid, an input circuit containing two
changer being delivered over a transmission line
to a tunable intermediate‘frequency ampli?er. 15 sources of electrical variations connected between
the control grid and ground, a feedback path be
In such a case it will probably be very inconven
tween the anode and control grid circuits com
ient to have to tune the output circuit of the fre
quency changer in conjunction with the tuning
prising an impedance element connected between
the cathode and ground, a low impedance aperi
of the intermediate frequency ampli?er, since
some kind of remotely controlled ganging ar 20 odic load connected across the said element, and
means for conditioning the valve in such manner
rangement would be needed. Moreover, proper
impedance matching between the output circuit
of the frequency changer and the transmission
line practically necessitates that the output cir
as to produce in the said load a beat variation
from the said sources of variations.
A practical embodiment will be described in
cuit impedance should be a pure resistance over 25 order to illustrate the invention.
the frequency range concerned, and this makes
a semi-aperiodic arrangement impracticable.
Inasmuch as the load presented to the frequen
cy changer by the transmission line and the in
put circuits of the intermediate frequency am
pli?ers may be very low for the form of receiver
The ?gure of the accompanying drawing shows
a schematic circuit diagram of the embodiment
which comprises a frequency changing arrange
ment. This is based on an experimental circuit
which gave satisfactory results, and it contains
a number of details of an unessential character
mentioned above, conventional frequency chang
ing arrangements, with aperiodic coupling, would
which could have been provided in several other
ways. In this ?gure the condensers designated
be very ine?icient.
K1 or K2 are by-pass or blocking condensers of
The principal object of the invention is to pro 35 negligible impedance at the frequencies con
vide a simple modulating arrangement which
The circuit comprises a modulating valve V,
may be efficiently coupled and matched to an
aperiodic load of low impedance.
According to the invention, there is provided
an electrical modulating or demodulating ar
shown as a pentode, having a resistance R1 con
necting the cathode is to ‘earth. The anode a is
40 connected at 4 to the positive terminal of the
high tension source I-ITI through resistances R3
and R4, and the screen grid in is connected to
the same source through resistances R5 and Rs.
By-pass condensers K1 are shown connecting the
back between such circuits, means for simultane 45 junction points of these resistances to earth to
form a well known decoupling arrangement. The
ously applying a signal wave and a carrier Wave
suppressor grid 92 is connected to earth,
to the input circuit of the valve, means for bias
The radio frequency signals and the carrier
sing the valve in such manner that the applied
waves are supplied simultaneously to the control
waves cause the anode current to vary over a
substantially curved portion of the valve char 50 grid as from terminals I and 2 respectively. The
inductance coilsLz, L3 and adjustable condensers
acteristic curve, and output means connected to
C2, C3 form a radio frequency band ?lter through
the said impedance for extracting the modulation
rangement comprising a thermionic valve having
an impedance connected in series with the cath
ode in both the input and output circuits of the
valve for the purpose of providing negative feed
products from the valve.
which the radio frequency signal and carrier
waves are applied to the control grid 9/3. The
quency changer comprising a_ thermionic valve 55 radio frequency signals are applied to the center
The invention also provides an electrical fre
point of coil L2. They are obtained through ra
dio frequency input terminals I from the anode
circuit of a valve (not shown) which derives high
Valve V, Mazda SP. 41, R. F. pentode:
tension voltage from the source HT2 at termi
nal 5 through the coil L2. The inductance .0011
L1 is a coupling coil through which the carrier
Waves are’ supplied from oscillator input termie
nals 2 to the control grid 93. The resistance R2 5.
V t
and shunting by-pass condenser K1 are details
of the input ?ltering arrangements and do not 10
affect the operation of the valve V. The method
of applying the waves to the valve is immaterial
as regards the invention, and any other suitable
means could be used instead.
The following details of the relevant compo
nents are given:
-Resistance R1 ____ __,_ ______ __ohms__
.jResistance R3 ______ __, ______ __do_',___
Resistance R4 _____________ __'_d0____ 4,700’
Resistance R5 ______________ __do____ 10,000
Resistance Rs ______________ __do____ 20,000
Condenser C1___micro-microfarads;_
‘ Condenser K1 ________ __rnicrofarad_g
_; Condenser _Kz__' ____________ __do____
I 7 Voltage HTl ______________ __v_volts__
1 Under 'th‘eseiconditions the cathode current was
The valve V should preferably have a high 15 about"7;5‘ milliamps, so that the control grid was
mutual conductance, and is so biassed, and/or ’ biassed negatively, to the cathode by about 1.5
volts. “The peak signal voltage applied to the
the level of the input signals is so chosen, that the
anode current swings over a substantially curved
control grid was arranged to be about 2 volts.
portion of the valve characteristic, whereby the '
It should be clearly understood that these par
valve acts as a modulator or recti?er.
20 ticulars are given for illustration only and in
The‘ resistance Ri' ‘sasia low value, and the
other circumstances quite different components
intermediate frequency signals are taken from
and values might be used. The same principles
are applicable whatever the ranges of the signal
the terminals of thisdresistance through a co
axial transmission line T connected at terminals
and intermediate frequencies may be; for exam
3 to amplifying equipment (not shown). A large 25 ple, the intermediatefrequency may be represent
blocking condenser K2 is provided, but may not
ed by the ?nally demodulated signals, which may
benecessary in all cases. The resistance R1 is
be of audio frequency. The value would then be
shunted by a small condenser C1 for the purpose
acting’as a ?nal demodulating valve. Thus the
of byV-passing the radio frequency waves.
arrangement couldnbev ‘coupled vefficiently and di
It will be seen that as regards the intermedi 30' rectly to’ a‘ low impedance device such as a mov
ate frequency the arrangement ‘is similar to the
ing coil loud speaker. Similarly if the radio fre
'well known cathode follower amplifying circuit,
but the difference lies in the fact that the valve
is operated so that it acts as a recti?er.
quency output signals were replaced by the audio
frequency output of a microphone, for example,
the valve'would be acting as an initial modulator.
resistance R1 provides negative feedback at the
intermediate frequency and there are thus ob
tained the well‘known advantages resulting from
negative feedback. In particular, the resistance
R1 'may be chosen so that the' low impedance of
the co-axial line or other output circuit is prop
erly matched. In this way an aperiodic coupling
arrangement of 'maximum ef?ciency is obtained
in a very simple way by which the intermediate
valve'forming a negative ‘feedback path ‘between _
frequency signals'may be directly extracted from
said circuits, means for ‘simultaneously applying
the modulating valve without the use of any trans
formers or tuned circuits.
It'will’ be evident that many of the details
shown in‘ the ?gure are unessential, and any
cuit of‘ said valve, means for predeterminedly bias
sing said valve'with potentials so chosen that said
applied waves" cause .the anode ‘current of said
vWhat is claimed is:
1. An electrical device for securing changes of
modulation" by the algebraicaddition of waves of
differing frequencies; including a thermionic
valve having‘ electrodes including'a cathode, in
put and output circuits therefor, an‘ impedance
connected in series with said cathode and insert
ed in both the input and‘ output circuits of said
a signal wave and. a carrier wave to the input cir
valve to vary over a substantially curved portion
other arrangements performing the same func
tions could ‘be used instead. The important 50 of the characteristic curve 'thereof; and output
points, however, are
means connected to ‘at least a ‘portion of said im
pedance for extracting‘the modulation products " "
(1)’ The resistance R1 should preferably be
from said valve.
‘ ' *
chosen so that the output load impedance is
2. An electrical frequency changer including 'a
matched at the intermediate frequency.
(2) The radio frequency signals and carrier 55 thermionic valve connected in? a ‘cathode follower
circuit and ‘having, electrodes including ‘a control
waves should be applied simultaneously to the
grid and- a'cathode, a resistance'connected in
series with the cathode of; said valve, means for
(3) The valve should be so biassed and/ or the
applying simultaneously tosaid control grid two
signal level should be so adjusted that the anode
current swings over a substantially curved portion
of the valve characteristic,‘ or, in other words,
so that the valve acts as a recti?er.
series of input waves having differing frequencies,
means for~ biassing said valve with potentials‘so
chosen’ that said valve operates as a recti?er, and
low impedance output means connected'to at least
a 'portion of said resistance for extracting there
It will be‘ evident that these requirements can
be met in a number of other ways. For exam
ple, the valve V is not essentially a pentode; a 65 from'waves having-a frequency equal to the‘dif
ference of said input waves of differing‘ frequen
triode or'tetrode could'have been used, or a valve
with two control grids to which the radio fre
quency signals and carrier waves are separately
3. A modulation'changin‘g circuit. including a
thermionic ‘valve: having a cathode, anode and
In a particular-case of the circuit of the accom~ 70 control grid, an input circuit for said valve, means
panying drawing which gave good results, the
for, simultaneously; supplying said input' circuit
radio frequency was in the range 30 to 40 mega
with two series of electrical variations of differing
cycles, and the intermediate frequency was varia
frequencies, means for connecting said input cir-'
ble over the range 3 to 4 megacycles.
The co
axial line T had an impedance of 70 ohms.
cuit between said control gridiand ground, afeed
' 75 back path connected betweensaid anode and con
trol grid circuits and comprising an impedance
element connected between said cathode and
ground, a low impedance aperiodic 1oad connected
across at least part of said impedance element,
and means for conditioning said valve with poten
grid intermediate between the control grid and
tials s0 chosen as to produce in said load a beat
variation derived from said sources of electrical
the anode thereof, and means for applying a
suitable potential to said screen grid.
5. A device according to claim 3, in which said
aperiodic load connected to said impedance ele
ment includes a co-axial transmission line, where
by all load tuning can be effected at the farther
end of said transmission line.
4. A device according to claim 2, in which said
thermionic valve is of the type having a screen 10
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