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Патент USA US2107425

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Feb. 8, 1938.
?Uba KtrLKtNbl:
Filed Aug. 20, 1936
Patented Feb. 8, 1938
Curt Protze, Berlin, Germany, assignor to Tele
funken Gesellschaft fiir Drahtlose Telegraphic
m. b. H., Berlin, Germany, a corporation of
Application August 20, 1936, Serial No. 96,980
In Germany July 13, 1935
3 Claims.
In the wireless communication it is often de
sirable for the telegraph operator to be able to
hear his own telegraph signals as produced in
the transmitter in order to be able to control the
6 working of his transmitter. For this supervision
it is necessary to be sure that the high frequency
power is actually being sent out. It should be
kept in mind that this could not be readily ascer
tained where the control arrangement or moni
10 toring means is placed directly in the keying cir
cuit, since it is possible that failure may take place
within the individual stages of the transmitter
and not be noticeable to the operator.
Where a supervisory control for the entire
15 transmitter is required there exists the disadvan
tage that the controlling volume, i. e., the moni
toring signals ?uctuate to a high degree unless
means to counteract this ?uctuation are provided.
In many cases the transmitter is not always op
20 erated with the same power, since at resumption
of communication a high power is used for send
ing to permit the transmitter easily to assume its
proper operating state. Thereafter the power is
reduced to a point just su?icient to retain the
25 volume necessary for communication.
Not only is the ?uctuation in the volume of
the transmitter of great inconvenience to the
telegraph operator, but eventually if the volume
becomes too large it will endanger the hearing of
30 the operator, and it will also not be possible for
the latter to hear the softer signals of the oppo
(01. 250-17)
addition it should be borne in mind that for com
mercial communication, tubes having different
over-all dimensions are used whereas modern
multiple electrode tubes as used in receivers, are
not as yet manufactured in the commercial trans
mission form. It would obviously be possible to
avoid such special tubes and not to avail one
self of the advantages thereof, but the circuits
hitherto known have the disadvantage that the
control arrangements are sensitive to variations 10
in the operating voltages, and that even the tubes
of the same type diifer as to their characteristics,
so that therefore the position of the lower bend
of the characteristic is not established with su?l
cient accuracy.
In accordance with the present invention, the
constant volume in an audible control device for
transmitted telegraph signals is attained in that
the high frequency derived from the transmitter
and then detected is applied to the grid of a tube 20
serving as control organ or element for the re
ceiving indicator, whereby the grid potential of
said tube is prevented from becoming more posi
tive under the in?uence of a counter potential de
spite an increase in the detected positive potential, - 25
said counter potential being produced by the grid
current at an ohmic resistor placed in the grid
lead. Thepinvention may be put into practice by
connecting the tube serving as control organ in
the plate circuit of a low frequency generator,v 30
and negatively biasing the grid of said control
site station with su?icient clarity directly after his ' tube to such a degree that it will be blocked when
hearing has been jeopardized on account of too
large a volume.
For this reason an automatic
35 volume control is greatly desirable.
The arrangement heretofore used was such that
the detected high frequency fails, thereby,-stop
ping the generator owing to a cutting off of the
plate potential.
This arrangement will now be elucidated with
the high frequency obtained from the transmitter
reference to the single ?gure in the drawing
has been detected, and the direct potential so ob
tained has been utilized as plate potential of a
40 tube arranged as tone frequency generator. How
wherein I have illustrated one embodiment of
my monitoring circuit.
The keyed high fre
ever, in this case a sufficiently constant volume was
quency is supplied from the transmitter across
condenser C to the detector tube I , whereby said
not attainable since the plate potential of the
tone frequency generator and hence the ampli
high frequency may be derived from the antenna
tude of the tone produced varies with the energy
45 of the transmitter to be controlled.
An automatic volume control such as known for
instance in broadcast reception could be used.
However, this involves di?iculties since for com
mercial communication several other require
50 ments must be ful?lled. It is not advisable to
use special control tubes such as hexodes in tele
graphy systems for instance, since owing to the
desire of reducing the number of spare tubes to a
minimum, the number of different types of tubes
55 in a receiver should be as small as possible. In
or from an intermediate circuit for instance, al
though as is obvious, it may also be inductively
transmitted to coil Sp. The high frequency po 45
tential appearing at the ends of coil Sp will be
detected in tube l, which by the way, may be a
single grid tube to avoid increasing the number of
types of tubes, the grid of said tube being con
nected to the cathode or anode.
There appears at the terminals of resistor W a
direct-current potential of the rhythm of the
keyed signals, the value of which depends upon
the power to which the transmitter is adjusted to
send out. The time constant of the circuit con 55
sisting of resistor W and condenser C1 is suffi
ciently short to avoid distortion of the signals at
the highest telegraph speeds. The produced di
rect potential is applied to the grid of tube 2 in
such-manner that it opposes the negative bias of
battery V. During the pauses of the operator's
own transmitter no voltage exists at resistor W so
that only the biasing potential V is e?ective, and
which is just sumcient to block the tube 2. Con
10 sequently owing to the then existing high direct
current resistance of tube 2, the plate potential
applied between -—A and +A will be substantially
distributed over the impedance of tube 2, thus pre
venting the tube 3 from oscillating owing to in
15 su?icient plate potential so that no tone can be
heard in the head piece T. But the receiver can
then be heard across the conductors shown.
If operator’s own transmitter is being keyed,
a direct potential appears at W imparting to the
20 grid of tube 2 a more positive bias thereby re
ducing its direct current resistance. Then tube
3 receives plate potential and oscillates. Up to
this point the arrangement does not offer any ad
vantage in reduction of loud signals in the moni
tors’ phones in the presence of high amplitude
telegraphy, since for higher direct potential at W,
the plate potential on 3 likewise increases. This
is avoided however, in the present invention by
utilizing the condition that the grid current ?ow
30 ing in tube 2 produces in resistor R placed in the
grid circuit a negative, and hence opposing po
tential. This opposing potential as is obvious, is
also produced at W, but in view of the afore
mentioned short time constant W is but a low
35 ohm resistor, whereas the value of R is approxi
mately equal to 500,000 ohms.
0n the other hand, it will not be possible to
maintain a short time constant by decreasing
01 while providing a large value for W, since C1
40 is to represent a su?icient short circuit as re
gards high frequency. If, therefore, the potential
appearing at W exceeds the biasing potential V
so that a positive bias exists at tube 2 producing
a grid current, this increasing positive potential
45 at W owing to the opposing potential at R causes
a but very slightly higher positive potential at
the grid of tube 2. Moreover, in view of this fact
the direct current resistance of tube 2 and hence
the plate potential at tube 3 will be constant, and
50 therefore also the volume will have the same value
despite varying high frequency intensity.
The advantage of the arrangement resides in
that with few auxiliary means it is possible to
obtain a constant volume throughout a very wide
55 signal amplitude range, and that changing the
controlling tube 2 owing to the relatively constant
grid current development, does not cause a change
in the operating condition.
As already pointed out, the range of constant
volume begins only when grid current ?ow be
gins, i. e., when the negative biasing potential V
is overcome. However, this is no disadvantage
since for instance at a fluctuation of the trans
mitter power at the ratio of for instance 1:1000
(for instance between 20 w. and 20 kw.) and at
a corresponding fluctuation of the voltage am
plitude at the ratio of 1:33, the audible control
device can be coupled to the transmitter in such
70 a way that at the lowest power of 20 w. which
appears, grid current starts already.
Furthermore the feedback of tube 3 can be so
dimensioned that it still remains in the non-oscil
lating state at low plate potentials. Finally, by
75 causing the tube 3 to oscillate at excessive poten
tial, the constancy of the volume can be still
further enhanced.
I claim:
1. In a device for producing monitoring sig
nals indicative of the operativeness of a trans
mitter and for controlling the intensity of the sig
nals produced, an oscillator including an electron
discharge tube having electrodes connected in os
cillation producing‘circuits, one of which circuits
includes a source of potential su?icient to produce 10
oscillations in said tube and circuit, a second elec
tron discharge device having its impedance con
nected with said one of said circuits and source
of potential to control the value of the potential
applied by said circuit to one 01’ said electrodes, 15
said discharge device having a control grid and
a circuit therefor including means for normally
biasing said device to a point at which said sec
ond device impedance is high and oscillations are
cut off in said ?rst tube-and circuit, a resistance 20
connected with said control grid, rectifying means
connected with said resistance for producing a
potential therein opposing the normal potential
applied to said control grid whereby oscillations
may be produced in said oscillation generator tube 25
and circuits, means for impressing Wave energy
to be monitored on said recti?er, and additional
means for producing an additional potential drop
which opposes said potential drop produced in
said resistance when direct current ?ows in to the
grid of said second named device.
2. In a system for producing indications of the
presence of wave energy in the output of a trans
mitter and maintaining said indications of sub
stantially constant amplitude, an oscillator com
prising an electron discharge device having its
electrodes connected in oscillation producing cir
cuits, tube impedance means and a source of po
tential connected in one of said circuits of said
device for charging an electrode of said device to
a potential relative to its cathode at which said
device is substantially cut off, and oscillations are
not produced in said tube and circuits, recti?er
means energized by and responsive to wave energy
to produce a. controlling potential, means con
necting said recti?er to said tube impedance
means to control the impedance thereof, in the
presence of said produced potential to increase
said potential to which said electrode is charged
relative to said cathode to cause said device and
circuits to produce oscillations, additional means
for producing a potential which opposes said ?rst
named controlling potential in the presence of
oscillations of substantial amplitude in said device
and circuits, and an indicator coupled to said.
3. In a device for indicating the presence of
the wave energy sent out from a transmitter and
for producing indications thereof of substantially
constant amplitude in an indicator, an electron» 60
discharge device having an anode, a cathode, and
a control grid connected in oscillation producing
circuits, one of which includes a source of po
tential, a second electron discharge device hav
ing an anode and a cathode connected in said last. 65
named circuit, said second device having a con
trol grid, a source of potential for normally bias
ing said control grid negative relative to said
cathode to increase the impedance of said second
device to lower the potential on the electrodes of 70
said ?rst named device to prevent the production
of oscillations in said ?rst named device and cir
cuits, a recti?er having input electrodes excited
by wave energy from the transmitter and having
output electrodes connected with a resistance in 75
which a. potential drop of a value characteristic
of the intensity of the wave energy of the trans
mitter is produced, means for connecting said
resistance to the control grid and cathode of said
second named device in a sense to overcome said
normal negative bias whereby oscillatory energy
is produced in said ?rst named device and re
sistive means in the control grid and cathode
circuit of said second named device for produc—
ing a potential in the presence of grid current
therein which opposes the potential produced in
the resistance connected with the output of said
recti?er and an indicator coupled with said ?rst 5
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