US1896785A - Modulating device - Google Patents

Description

Feb. 7, 1933. R. s OHL 1,896,785

y MODULATING DEVICE Filed July l, 1931 Haz 2f ATTORNEY I Patented Feb. 7, 19/33 These currents represent respectively the in- UNITED lSTA E1s- PATENT oFFlcl-z nUssELL' s. om., or sIILvEn, NEW JERSEY, ASsmNon 'ro EEEI.` 'rELErnoNE' LABORATORIES, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF NEW Yom:

I .nonupumc DEVICE Application :Bled J'uly 1, 1931. Serial No. 548,079.

This invention relates to heterodyne detectors and modulators of the space discharge type and more particularly to detectorarrangements for use in systems where'strong heterodyne currents are combined with Weak incoming signal currents, or where the heterodyne frequency is relatively close to the frequenc of the incomingsignals.

In hetero yne detectors currents of three different frequencies arev usually involved.

coming signal, the heterodyne oscillation and the ,detected output` or beat frequenc current. It is important to be able to a just the circuits of the detector to control the l amplitude of each current without disturbing or changing the amplitude of either of -ing" electrode.

lthe other currents in so doing. This necessi- 'tates separate circuits for each frequency which are substantially independent of each other, that is, circuits which have no mutual reactions.- v

Inaccordance with rthe invention a space dischar e device is provided having a catli-I ode an anode, a control electrode,v a screen id, and in some cases an additional shield- AWhen the space discharge device-is used as a heterodyne detector, t e

incoming signals are impressed upon the control electrode. The local oscillator is connected to the anode and the beat frequency or detector current output is taken from the screen grid. The screen grid vperforms its usual function 4as a shield or screen between the anode and the control electrode as in the various forms of radio frequency amplifiers employing the so called screen grid` tubes, and in addition, the screen grid serves as an auxilary anode to which is connected a load Allleterodyning oscillations from, the following specification and the ac` v companying drawing in which:

Fig. 1' shows a portion f a radio receiving lsystem employing the invention; and

2 shows a similar 'system -in which an auxlliary shielding electrode has been introde 1-7, a screen grid 19, and an anode 20. A local source 21 of continuous oscillations y is coupled through a transformer 22 to the anode 20. The screen grid 19 is grounded through a circuit 23 which is resonant/to the frequency of the detected output currents originating in the space discharge device 15. y

The tuned circuit 23is' coupled by means of an adjustable coupling transformer 24:l

with a similar tuned circuit 25 which latter circuit is connected with a space discharge device 26 which may be an amplifier. The

control grid 17 is connected with an antenna 10 through a tuned circuit comprising an inductancell and a variable condenser 12. The tuned circuit 11, 12 is connected through a fixed condenser 13 to ground 14. The cathode 16 is directly grounded at one-end and' is 'connected to ground at the other end through resistances 27 and 28 and a filament connected to any suitable load circuit' through a/pair of terminals 31 and 32.

In the operation of the system of Fig 1,

incomingr signals are received upon the antenna 10 and are impressed by means of the tuned circuit 11, 12' upon thev control-grid 17. l are impressed upon the anode by the localsource or generatnr 21'acting through the transformer 22.

By. the well'known modulating or detecting action of the space discharge device 15combination currents are produced, the most commonly used of which have a frequency determined by the difference between the frequencies of the incoming signals and of the `local oscillations. Output currents of the difference frequency are selectively received heating battery 29. A suitable grid biasing in the tuned circuits 23 and 25 and impressed upon the space discharge.- device 26. The tuned circuit 23 offers a large impedance for the difference frequency, causing currents of that frequency to be eiiciently transmitted through the coupling device 24 to the tuned circuit 25 and the space discharge device 26. The impedance of the circuit 23 for the heterodyne frequency of the generator 21 is relatively very small. Because of this small impedance the screen grid 19 is) effectively grounded at the heterodyne frequency through the circuit 23 with the result that the screen grid 19 serves to screen the anode -2O from the control grid 17 in the same' manner as the screen grid in a radio frequency amplifier employing a screen grid tube. Due to the screening which is provided, the local oscillations, which ma be very strong, aref" tively high and close together any coupling ,l

of the several tuned circuits with one another such as that due to electrostatic capacity between the detector electrodes tends to make the adjustment of one circuit affect the adjustmentof the others. Such interaction of the circuits is diminished by the isolation afforded by the use of separate electrodes and by the screening effect of screen grid 19 and may be ractically completely eliminated. Due to t e absence of reaction, the local source 21 may be adjusted in frequency and amplitude without disturbing the tuning of circuit 11, 12 and the circuit v11, 12 may be tuned without affecting either the frequency or amplitude of 'the oscillations generated by local source 21.

The system of Fig. 2' differs from that of Fig. 1 in the addition of an auxiliary shielding element. .This shielding element comprlses a perforated or woven shield 18 inserted between the control grid 17 and the screen grid 19. The shield 18 is directly connected to ground 14. i

The operation of the system of Fig. 2 is similar to that of Fig. 1 -The presence of the additional screen or shield 18A increases the shielding effect between the control grid 17 and the anode 20. The shield 18 also serves to screen the control grid 17 from the screen grid 19, preventing reaction between the respective tuned circuits 11, 12 and 23, 24, 25.

While in a detecting system the frequency of the output current 4is considerably below the frequency of the input current in the usual case, the invention may equally well be applled to a modulatin device in which the output frequency is hig er than the input frequency. The advantages of the arrange' ment disclosed are not solely dependent upon the.k particular selection of input and output fre uencies emplo ed. 4

. hat is claime is: i

1. A modulating system comprising a space discharge device having a cathode, an anode, i'

a control grid, and a screen grid positioned between said anode and said control grid, two

sources of currents tol be combined, means (for connecting one of said sources to `said control grid and to said cathode, means for connecting the other of'said sources to said anode and to said cathode, andmeans con- Lcathode, means for-connecting the other of said sources to said anode and to said cathode, and means connected to said shield electrode and to said cathode for utilizing combination currents generated in said space discharge device.

3. A modulating system comprising a space discharge device having a cathode, an anode, a control grid, and a screen grid positioned between said anode and said control rid, three branch circuits connected to sai cathode, each of said circuits being connected to adif ferent one of the remaining electrodes, a source of incoming si al current connected in the branch circuit eading to said control grid, a second source of alternating current in the branch circuit leading to the anode, and means associated with the branch circuit leading to the screen bination currents.

4. A modulating system comprising a space discharge device having acathode, an anode, a control grid, and a screen grid posi- .tioned between said anode and said control grid, a separate circuit from said cathode to each of said other electrodes, sources of imlos grid for utilizing vcompressed waves in two of said circuits, one of said sources being connected to said control grid and the other source being connected to the anode, and means associated with` the screen grid circuit for utilizing output current.

5. A heterodyne detector comprising a space discharge device having a cathode an anode, a control grid and a screen id for shielding said control grid from sai anode, l

a source of waves to be detected, means for mpressmg waves from said source upon said space discharge device through said control grid, a source of oscillations to be combined A with said waves,'said source of being connected to said device i through the anode, and e load circmt for utlizing combinationcurrents connected to said space discharge device through said screen grid; said load be tuned to discriminate between said tion and said combinatlion cl'rents1 s I '6. eter yne etector comprising a space discharge device having e'cathode, an anodez a'. control grid and screen 'd for shielding said control grid from sai anode,

asource ofwaves to be detected, means for impressin waves from said source on said space disc rge device through control grid, a source of oscillationsof sllghtly differentV uency from said wa'ves to be detected, sai source being connected to said ece discharge device through th`e anode, e ond circuit connected between said screen id and the cathode for u combnat1on`currents of relatively low` uency, said lodd Y circuit being antlresonant at the frequency .of said vcombination currents, whereby the impedance of said load circuit is made negli-A,

gible at thefrequency of said oscillations and said screen grid effectively revents interaction between said source o waves :ind seid source of oscillations.

Y In witness whereof,l I hereunto subscri my Yname this 30th da. of June, 1931*. g USSELL S. OHL.

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