US2234584A - Short wave reception - Google Patents

Description

March M, 1.941.l B TREVOR ETAL SHORT WAVE RECEPTION' original Filed Dec. e, 1935 Patented Mar. 11, 1941 UNITED STATES PATENT OFFICE SHORT WAvEfREcEPTIoN original application December 6, 1935, serial No.

53,136. Divided and this 19, 1938, Serial No. 185,722

application January 1c claims. (o1. 17e-.44)

The present invention is a division of our copending application Serial No. 53,136, iiled December l6, 1935, now United States Patent'No. "2,152,335, granted March 28, 1939, and relates to improvements in band pass transformers or frequency selective circuits.

An object of the invention is to provide an Y improved signal selecting circuit for use at very short waves, so as to properly feed the desired vsignal into the first detecton'grid, orinput circuit. A suitable selecting circuit consists, according to our present invention, of a'metallic rod, pipe or'tube grounded at one end andn adjusted in length so as to resonate at the desired incoming carrier frequency. The antenna can be connected to one point'along this rod and the gridof 'the first detector to another point along the rod, so chosen 'as to suitably load the rod and at the same time derive from the road or tube a suitable excitation voltage for the `lirst detector. Such an arrangement, however,- in general would. suffer from the disadvantage of 'being too selective and being rather diiiicult to adjust.4

Toovercome these objections is a still further object of our present invention, and this 'object we accomplish by providing a tuning condenser at the Vfar end, that is atthe ungrounded endof the rod, so as to permit ease of tuning. To broaden the frequency pass band'of therod', resistance is added to the" circuit in a way which is described more fully hereinafter. In" addition, we find it advisable to shield the yrod ortubeby adding a grounded metalliccylinder around the tube.

This single rod arrangement, while it o'ifers much that is to be desired, still lacks; in certain instances, the ability to pass a suii'iciently Wide band of frequencies into the first detectonparticularly when the short Wave receiver is used, for example, for facsimile work.V Accordingly, a, 'further object of oui` present invention is to provide an improved tube or rod circuit making use of a multiplicity-of tubes or rods, preferably having overlapping resonance characteristics Such that, in toto, the group of rods is connected to serve as a rband pass filter passing the desired bandof frequencies into the iirst detector.

Other objects and features will appear from a reading of the following detailed description-of the invention in conjunction with a drawing Whose single figure illustrates, schematically, the selective circuit of the invention in 'an improved ultra short wave system. The system illustrated in the drawing is given by wayof example only,

' associated metallic cylinders and is not to be construed as limiting the application of the invention to other systems or circuits. i Referring to the drawing, high frequency energy is picked up on any suitable antenna, such as the diamond antenna 2, and fed to the primary 4 of the transformer variably coupled to the secondary 6. The two windings are electrostatically screened from each other by a screen diagrammatically indicated Vat 8 and vmounted within a metallic cylinder I0,`in turn facing into and electrically and physically connected to the cylinder I2. Concentrically mounted within the cylinder I2 therev is a rod, tube, or metal pipe I4, grounded at its left-hand end I6 and connected Vto ground at its right-hand end Vthrough a damping resistor- I8 and variable tuning condenser 20, the combination forming a non-radiating highly selectivecircuit. The metal-rod I4 within the metalcylinder I2" forms a' sharply selective inlput circuit, standing current waves being set up thereon by virtue o'f the input from the secondary 6 and by virtue of the tuning of condenser 20. In order to widen the band Width of this sharply selective prcselector circuit, the damping resistance I8 has been provided.

The received energy resonated in the rod I4 and condenser 20 is fed through a low impedance connection 22 to a second rod, tube or metallic pipe 24 mounted within a second cylinder 26 which is grounded, as shown. 'I'he far end of the second rod 24 is tuned by means of the variable tuning condenser 28. The rod 2'4 and condenser 28 form a second non-radiating highly selective circuit and are adjusted to have a resonance curve which overlaps the resonance curveof A'the rod I4-condenser 20 combination. In this way the vfrequency pass band width of the two preselector circuits I4, 20, I2 and 24,

28, 26`is further widened.

That is to say, the two rods I4, 24 with their I2 and 26, the damping'resistor I8, and the tuning condensers 20, 28 form a preselector lter for our improved ultra-short wavelength radio receiver. Coupling betweenthe ,tuned circuits of our improved filter is adjusted byvarying the taps of the low im- .pedance connection 22 along the rods I4, 24. It

is to be noted-that atthese high frequencies the grid of the detector tube presents a resistance, .load to rod 24 which forms part of the damping of the transformer systeml I2, I4, 24, 26, I8, 20,

The received filtered energy is fed through lead 30 onto the grid 32 of the high-frequency detector tube 34 which, in addition, is provided with a heating filament 36, a heater surface or cathode 38 and a plate or anode 40. Local highfrequency oscillatory energy is injected into the detector tube 34 through the cathode leads, as will be explained more fully hereinafter, and the beat-frequency energy is resonated irl the plate circuit of the rst detector 34 by means of the tuning coil 42 and the tuning condenser 44, both of which are adjusted to the beat frequency. The beat frequency energy is fed through the bypassing condenser 46 and intermediate-frequency energy leadl A to the intermediate-frequency amplifer.

The rst local oscillation generator is provided with a vacuum tube 48 having a grid 50, a cathode 52, 'a heating filament 54 and a plate or anode 56. The platecircuit of the tube 48 is provided with a plate tuning coil 58, a plate tuning condenser 60, a by-passing condenser 62. Plate voltage is `fedthrough the lead 64 which is kept at ground lrado-'frequency potential by the action of the lbypassing condenser 62`, and also the resistance con- --denser lters 66, 68 and 10, 12, housed within the ashieldingcompartment 14, 16. Within the shield 14', 16 there are also provided the coil and conldenser'filters 18, 80 and 82, 84, which, together with the by-passing condensers 86, closely adjacent `to the heater filament 54, maintain the heater at ground radio-frequency potential.

`Proper grid bias .is maintained by the action of `tl'iecondenser and grid-leak combination 8l'.

oscillations are generated because of plate-to- Vgrid interelectrode feed-back, and the frequency of oscillations is maintained constant by virtue of the improved frequency-controlling grid circuit, which will now be described in detail The radio-freqnency grid tank circuit rfor the oscillator 48 is formed of a cast metal cylinder 90 having a grounded base portion 92. From the vbase portion and integral therewith ythere extends the central projection 94, whichin turn is capped with a cast metal disc 96. Screwed into the open end of the cast metal cylinder 90, opposite the base 92, is another cast metal disc 99. vThis structure forms a high-frequency'tuned circuit of eX- ceptionally good mechanical vrigidity and is made of metal of low temperature coefficient, such as Invar, and will maintain its electrical characteristics constant over a wide range of temperature. hence insuring constancy of 'frequency of oper- -ation of the first oscillator 48.

In general, it may bevsaid that the confronting surfaces of the disc 96 and the screw threaded disc-98 form a low-loss condenser, and the length of the metallic projection between the disc 96 and `the base 92, a low-loss inductor. This grid circuit is non-radiating, since the lines of flux are 'all contained within the cylinder 90, the base 92 and the disc 98. These latter elements, namely the outer surfaces of the base 92, cylinder and Vdisc 98, are maintained at ground radio-frequency potential, and can be directly grounded, if desired, for direct currents as well.

From another viewpoint it may be said that vhigh-frequency currents surge back and forth along the length of direction `of the outer cylindrical surface of vthe projection 94, as a consequence of which the magnetic 'flux lines travel circularly in thespace between the projection 94 and the cylinder 90. As the high-frequency currents flow back and forth at an exceedingly high rate, the flux lines build up and collapse through 'the cathode conductor |00 connected to the cathode 38 of the detector tube 34, and `also through the heating leads |02 for the heater 36 of the first detector 34.

The frequency of the local oscillator is adjusted by screwing the metal disc 98 towards or away from the metallic disc 96. A micrometer 5 gauge |04, bearing at one side and supported by the fixed supports |06, and at its ,other-movable side |08 upon the disc 98, serves as atuning indicator indicating the frequency of oscillations generated by the first local oscillation generator 48. l0

It Vhas already been pointed out that -the grid circuit for the local oscillator may be made of cast metal, such as copper, or of Invar with copper or silver plating after machining to size, so as to give a low-temperature coefficient of frequency 15 variation. In addition, or in the alternative, the entire oscillator may be placed in a temperature controlled oven, and/or placed in a room which is roughly temperature-controlled to still further enhance frequency stability.

Because of the lines of magnetic flux which build up and collapse through the cathode conductor |00 for the Vfirst detector 34, the cathode 38 of the detector vibrates in potential at the frequency of the oscillations produced by the local y25 oscillator 48. In addition, thegrid 32 of the rst detector 34 is vibrated through lead 30, as before explained, in potential and at the frequency of the incoming wave which may be of the order'of 100 megacycles or three Imeters in Wavelength. 30 VIthas been foundpreferable to operate the local oscillator 48 above theincomlng wave frequency to produce in the beat-frequency circuit 42, 44, and also in the beat-frequency lead A, beat-frequency energy of-the order of 28 megacycles. It 35 is yto be clearly understood, however, thatthese -gures are given simply by way of example, and `are not to be construed ln anyway as-1imitingthe "present invention to'these specific frequencies or wavelengths. A40 As was done with the case ofthe localoscillator 48, the first detector plate circuit is providedwith a grounding condenser ||0 and resistive and capacitive lters ||2, ||4 within the shielding compartments ||6, I8. Also, the vheating leads |02 l5 for the first detector filament 3,6, are provided vwith-the choke coil and condenser'lters |2`0, |24,

-circuit forthe first detector 34, which tank circuit consists of the tuning coil 42, the tuningi60 condenser` 44 and a resistance 45 broadening the frequency pass band of a plate circuit of the first detector 34.' The beat-frequency energy is fed through the lead A|28 to a suitable utilization circuit, such as an intermediate frequency amplifier, not shown.

The metal cylinders |2, 26 of the frequency selective circuit are preferably rigidly mounted 'against the base of the radio frequency tuned F circuit 90, 94, 96, 98 to provide for 'additlonalio mechanical and electrical stability. A housing is bolted against the-'base 90 and contains such elementsfas resistance |8 and condensers 20 and v28. Hollows maybe provided in the-casting 90,

92 so that the tubes 48 and 34, respectively the 7-5 Y of Xed or Zero alternating current potential.

What is claimed is:

1. In combination, a high frequency circuit comprising a metallic rod, a connection having very low impedance'to energy of the operating frequency from ground to a point on said rod, a variable condenser connecting another point on said rod to ground, and a resistance connected in shunt to a portion of said rod and ground, an `input circuit coupled to one portion of said inner conductor, and an output circuit coupled to another portion of said inner conductor.

2. In combination, a high frequency selective circuit comprising an inner conductor and a surrounding outer conductor directly connected together at one point in their lengths, a connection having very low impedance to energy of the o-perating frequency from said one point to ground, a variable condenser connecting said inner and outer conductors together at another point in their lengths, and a resistor connected across said inner and outer conductors at alocation removed from said first point, an input circuit coupled to said inner conductor at one place in its length, and an output circuit coupled to said inner conductor at another place in its length.

3. A lter circuit comprising a pair of linear conductors having overlapping resonance curves, an input circuit coupled between two points on one of said conductors, an output circuit connected to the other of said -conductors, and a connection devoid of concentrated reactance coupling said conductors together at points intermediate their ends.

4. Apparatus as lclaimed in claim 3, characterized by the fact that a grounded metallic shield is placed about each 'of said linear metallic conductors.

5. A filter comprising a linear metallic conductor grounded at one end, a grounded metallic shield about said conductor, a variable condenser connected from the free end of said conductor to ground, a resistance connected in shunt to a portion of said conductor, a second linear con ductor also grounded at one end, a grounded metallic shield about said second conductor, said second linear conductor cooperating with its shield to form a tuned circuit, and means for coupling said linear conductors together.

6. In combination, a tuned circuit comprising an inner andan outer conductor conductively coupled together at one end, another tuned circuit also comprising an inner and an outer conductor conductively coupled together at one end,

a connection from a point on one inner conductor intermediate its ends to a point on said other inner conductor intermediate its ends, an input circuit coupled to the conductors of only one of said tuned circuits, and an output circuit coupled to the conductors of the other tuned circuit.

7. A frequency selective circuit having, in combination, a tuned circuit comprising an inner and an outer conductor conductively coupled together at one end, another tuned circuit also comprising an inner and an outer conductor coupled togetherxat onefend, a connection from a point on one'inner conductor intermediate its ends toa point on said other inner conductor intermediate its ends, means for maintaining said outer conductors of said tuned circuits at a rela'- tively fixed radio frequency potential, an input circuit coupled to the conductors of only one of said tuned circuits, and an output circuit ycoupled to the conductors 'of the other'tuned 8. A frequency selective circuit having, in c ombination, a tuned circuit comprising van inner and an outer conductor conductively coupled together at one end, `an impedance connecting the other ends of said conductors together; an- 15 other tuned circuit also comprising an inner and an outer conductor coupled together at one end, an impedancealso co-nnecting the other ends of this last tuned circuittogether; a direct connection between said inner conductors of said tuned circuits; an input circuit coupled to the conductors of one tuned circuit; and an output circuit coupled to the conductors of the other tuned circuit. t l.

9. The combination with a frequency selective circuit having a tuned circuit comprising an inner and an outer conductor conductively coupled together at one end, and another tuned 'circuit also comprising an inner and an outer conductor coupled together at one end, means for maintaining said outer lconductors at a fixed radio frequency potential, a direct connection from a point on one inner conductor intermediate its ends to a point on the other inner conductor intermediate its ends, of an input circuit coupled to only one of said inner conductors at another point intermediate its ends, and an output circuit coupled to the other of said inner conductors.

10. A coupling circuit between a source of high frequency oscillations and ya load circuit, cornprising two frequency selective circuits each being a section of a coaxial line, the inner conductors of said lines being coupled together at locations intermediate their ends, an impedance connected in shunt to the conductors of one frequency selective concentric line for widening the pass band thereof, said source being coupled to one of said lines, and said load being coupled to the other of said lines.

11. A coupling circuit between -a source of high frequency oscillations and a load, comprising two frequency selective circuits` each being in the form of a concentric line having an inner and an outer conductor conductively coupled together at one end, a capacitive connection from a point on each inner conductor near its other end to its associated outer conductor, a damping resistor connecting one of said inner conductors to its associated outer conductor also near said last end for widening the frequency band Width of that frequency selective circuit of which it forms a part, and means coupling together the inner conductors of said two concentric lines.

12. A system in accordance with claim 10, characterized in this that said source of high frequency oscillations is coupled to the inner conductor of one of said concentric lines near the conductively coupled end thereof, and said load is coupled to the inner conductor of the other concentric line near the end removed from the conductively coupled end.

13. The combination with a frequency selective circuit having `a first tuned circuit comprising an inner and an outer conductor conductively lcoupled together at one end and capacitively rcoupled togetherrat the other end, and a second similarly arranged tuned circuit, one of said tuned circuits having means at the capacitively coupled end for broadening the frequency response characteristic thereof, a direct connection between points on said inner conductors intermediate the ends thereof, of an input circuit coupled to one of said inner conductors and an output circuit coupled to the other one of said inner conductors.

14. A lter circuit comprising a pair of linear conductors having overlapping resonance curves, means for widening the frequency response characteristic of one of said conductors, an input circuit coupled between two points on one of said conductors, an output circuit connected to the other of said conductors, and a connection devoid of concentrated reactance coupling said conductors together rat points intermediate their ends.

15. A band .pass selective circuit comprising a tuned circuithaving an inner and an outer conductor conductively coupled together at one of their adjacent ends and capacitively coupled to gether at their other adjacent ends, another similar tuned circuit having a resonance characteristic overlapping the resonance characteristic of the rst tuned circuit, a resistance connected being a resonance characteristic overlapping the resonance characteristic of the rst tuned circuit, a connection from each of said outer conductors to a point of relatively fixed radio frequency potential, a resistance connected between the inner and outer conductors of one of said tuned circuits for broadening the frequency pass band thereof, a connection between the inner conductors of said tuned circuits, an input circuit coupled to one tuned circuit and an output circuit coupled to the other tuned circuit.

BERTRAM TREVOR. RALPH W. GEORGE.

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