US2112967A - Transmitting system - Google Patents

Description

-April 5, .1938. Y F. H. KROGER' TRANSMITTING SYSTEM FiledJan. 24, 1955 ATTORNEY Patented Apr. 5, 1938 UNITED STATES TRANSMIT'EING SYSTEM Fred lli. Kroger, Rocky Point, N. Y., assigner tc Radio Corporation of America, a corporation of Delaware Application January 24, 1935, Seriai No. 3,259

ld Claims.

This invention relates to an improved short wave transmitting system.

An object of the present invention is to provide a very simple and highly efficient short wave f, transmitting system.

Another object is to provide a system which enables the transmission of modulated short wave signals over a very wide frequency band and with a substantially flat overall characteristic.

A further object is to provide a transmitter arrangement which has high frequency stability comparable with crystal control, but which dispenses with the use oi" piezo-electric crystals.

A still further object is to provide an eicient short wave system capable of radiating waves of the order of three meters, more or less, and of providing an output which when unmodulated is between 80 and 100 watts.

And a still further object is to provide a highly o advantageous assembly of elements which are inherently rugged and free from critical adjustments and the like.

A feature of the invention lies in the combination of single ended master oscillator and frequency control line, which requires no insulation in the mechanics of the line. The oscillator is thus in the simplest possible mechanical form and, with the provision of a simple circuit, reduces initial cost of equipment and maintenance to a minimum.

Another feature lies in the manner of mounting the equipment into a compact assembly which enables easy adjustment and maintenance of apparatus. The entire radio frequency assembly is mounted as an integral unit whereby there can be no geometrical change.

A further feature resides in the use of lecher wires for inductive coupling instead of lumped inductances, in order to obtain simplicity of tuning and higher operating efciency in the system. These lecher wires are used with trimming condensers so that with change in temperature there will be a minimum change of electrical constants.

One advantage of the invention is that the frequency is maintained constant as long as the oscillator is supplied with power which has reasonably constant voltage, that is, in a range plus or minus one percent, and without the use of 50 numerous accessories which require adjustment and maintenance.

Other objects, features and advantages will appear in the subsequent detailed description taken in conjunction with the accompanying drawing which shows, diagrammatically, a com- (Cl. Z50-17) plete transmitting system in accordance with thev Line l is a low loss concentric tube affair havingl inner and outer conductors, and has the effect of a sharply tuned resonant circuit whose reactance changes rapidly with frequency, and it is this characteristic which is utilized to keep the frequency of oscillator MO constant.` Since the resonant frequency of the concentric line is determined chiefly by its length, it is provided with a sylphon bellows and invar rod, or equivalent arrangement S for maintaining the overall length of the inner conductor constant despite ambient temperature fluctuations.

Line l is designed to be a quarter wave length long, electrically, for reasons of reliability and simplicity. The diameters of outer and inner concentric tubes are chosen to give a compromise between space economy and a high reciprocal of power factor; the outer tube serving as a support for the panels upon which are mounted substantially all the radio frequency units. For greater frequency stability, line l is made integral with the radio frequency units and kept free from vibration which is ltered out. In practice, the line and transmitter unit are suspended by very exible helical springs, and the entire unit secured to a rack which, in turn, is mounted on shock absorbers. For a more detailed description of line I as employed herein, reference is made to my 'copending application Serial No. 1489, filed January 12, 1935.

As an illustration of the frequency stability of the line, in using the twelfth harmonic of a crystal controlled oscillator for comparison, it was found that with a variation of 9 C. in ambient temperature, line l varied no more than the crystal which maintained Aits frequency within .0005% over this change in ambient temperature.

Line l is made single ended and the frequency produced by oscillator MO is doubled in the subsequent stage. Any other arrangement would, Ordinarily, give too long a line. In order to reifi v tion to each other.

duce possible undesirable reaction, the generated frequency is taken as one-half that radiated, which in one practical embodiment was 45.9 megacycles.

A thermo-galvanometer M is loosely coupled to the inner tube of line I by means of exposure plates for determining the amplitude of oscillations of the line.

Between grid 3 of vacuum tube MO and line there is provided the conventional grid leak GL which gives part of the bias for the grid, thus enabling automatic adjustment for variation in tubes.

The filament power leads for the legs of cathode K which are above ground potential and which are maintained at the same radio frequency potential by by-pass condenser 4, are part of a double coil 5 for controlling regeneration of oscillator MO. The double coil 5 serves to bring out the filament leads in known inductive rela- Condenser 1 is a Vernier for varying the inductance of coil 5, and condenser 6 is a by-pass condenser to ground. A spark discharge gap |00 serves as a protective circuit in case of breakdown of tube MO. The filament circuit tuning is arranged to give suiicient regeneration at the frequency of line but to cause 0scillations in MO to cease when line is short circuited.

A 220 volt, 60 cycle, alternating current som-ce energizes the filament of the oscillator through a transformer |06 and a copper oxide rectifier |05. The direct current obtained from rectifier |05 eliminates the small 120 cycle modulation which alternating current on the filament would cause due to the resulting variation in bias. All other filaments are supplied directly from the 60 cycle supply.

In the output of triode MO is a parallel tuned circuit comprising lumped inductance 9 and variable condenser 8 coupling oscillator MO to the grid of the following frequency doubler stage. Condenser 8 is a Vernier which provides a convenient mechanical method of varying inductance 9, and condenser I0 is a by-pass condenser to ground.

In one embodiment used in practice, master oscillator MO delivered about watts, of which about 20 watts went to the grid of the frequency doubler stage and 60 watts to line I. The tuning of condense-r 8 varies the ratio of the energy delivered by MO to the line and that delivered to the grid of the frequency doubler. The greater this ratio, the more will be the line current, and the less the excitation to the doubler grid, and at the same time the greater will be the frequency stability, as the line will be operating nearest to its natural frequency. A compromise is found preferable whereby frequency stability is satisfactory and there is sufficient grid excitation in the doubler to operate the intermediate amplifier at something less than best efficiency.

The frequency doubler stage comprises the vacuum tube FD which serves to excite the subsequent intermediate amplifier stage with energy of double the frequency of that obtained from oscillator MO. Grid I3 of tube FD is connected to the tuned input circuit comprising inductance I I and condenser I2 tuned to the frequency of the output of oscillator MO. Inductance is not tightly coupled to inductance 9 and optimum grid coupling is rather loose and is such as to give rather sharp tuning for grid and plate. The output of doubler tube FD comprises variable air condenser Il composed of two discs adjustable with respect to each other and lecher wires I8 and is tuned to twice the frequency of the master oscillator frequency.

A balancing air condenser 2| in the plate circuit of FD makes circuit I8 symmetrical with respect to ground and is set to a value approximately equal to the plate-grid capacity of FD; the condenser which consists of two discs adjustable with respect to each other is then varied until the voltage node of the plate circuit is approximately at its mechanical center, a condition which is indicated by equal drop in wave meter indication when places equal distances on each side of the mechanical center are contacted by a testing rod. Element I9 is a radio frequency air choke coil.

Tube FD is also provided with a grid leak GL', a protective spark gap IGI, filament tuning I5 to control regeneration, variable condenser I6 and condenser 58, which elements correspond respectively with elements GL, gap |00, double coil 5, condensers 'I and 5 previously described in connection with master oscillator MO and used for the same purposes. Other corresponding elements also appear in the subsequent power stages in respectively corresponding locations and for similar purposes, and hence will not be referred to later.

The intermediate power amplifier stage comprises a pair of push-pull connected vacuum tubes IPA and IP'A for amplifying the output of doubler stage FD and for exciting the grids of the succeeding power amplifier tubes. The input circuit of IPA and IPA comprises a lecher wire system 28 which is bridged by a tuning air condenser 3| and which is coupled to the lecher wires I0 in the output of frequency doubler FD. The coupling of doubler plate circuit I8 to intermediate amplifier grid circuit 28 is varied for optimum excitation of tubes IPA and IPA'. output circuit of this intermediate power stage also includes a pair of lecher wires 32 which are coupled through a lecher wire line |02 to the grids of the succeeding stage. An air condenser 29 composed of two spaced discs adjustable with respect to each other aids in tuning the lecher wires 32.

A pair of neutralizing air condensers 30, 34 compensate for the plate-grid capacities of the associated tubes. Element 33 is a combination of choke and parasitic resistor in the form of a coil of resistance wire, the resistance preventing push-push parasitic oscillations. A conventional grid bias GL2 is in series with choke 33.

The power amplifier or output stage also comprises a pair of push-pull vacuum tubes PA and PA which are arranged similarly to the tubes of the preceding intermediate amplifier stage. The purpose of this output stage is to further amplify the carrier oscillations, and it is this stage which is modulated and excites the antenna. The output of the power amplifier is of the same frequency as the intermediate amplifier and is coupled inductively to the load circuit consisting of an inductive arrangement 56 and load adjustment inductances 51, the latter each comprising ten turns of #10 wire, one inch in diameter and approximately two inches long.

For utilization purposes, it is preferred to employ an antenna comprising a plurality of doublets of the type described in Carter application Serial No. 342, filed January 4, 1935.

The transmitter is capable of being either frequency modulated or amplitude modulated by connecting switch blade 53 in the plate circuit The L Cil Sil

of the last power amplifier, either to the upper or lower contact respectively, and by using known modulating means, not shown.

The elements of the transmitter circuit are all completely shielded and mounted on panels supported by line l.

In tuning the short wave transmitter, the iilament tuning of MO is set so that the master oscillator will not oscillate when line l is short circuited, after which the lament tuning is set for maximum line current. In the intermediate stage, the neutralizing condensers are each first set at a capacity approximately equal to the plate-grid capacity of the tubes. Then, with no plate voltage and a grid meter in circuit, the grid circuit is tuned. The plate circuit is tuned next and the dip in the grid meter noted as the tuning point is passed through. The neutralizing condensers are each changed an equal amount and again the grid circuit is tuned. The plate circuit is also tuned again and the grid meter observed. If the dip in the meter is greater at the tuning point than previously, the neutralizing condensers should be changed in the opposite direction. This method oi setting the neutralizing condensers is continued until no dip is noted in the grid meter when the plate circuit is tuned, after which the grid meter is taken out of the circuit and the plate voltage applied, and the plate circuit again tuned, the last tuning being indicated by the wave meter. The coupling of the doubler plate circuit to the intermediate amplier grid circuit is varied or optimum exn citation of the intermediate amplifier. The nal power amplifier stage is tuned in the same manner indicated above for the intermediate amplifier stage.

What is claimed is:

l. In combination, an electron discharge device having anode, cathode, and grid electrodes, means for maintaining said cathode above ground radio frequency potential, a tuned input circuit connected between said grid and cathode electrodes, a source of radio frequency energy coupled to said input circuit, and a tuned output circuit connected between said anode and cathode, said tuned output circuit comprising a pair of lecher wires conductively connected together at one of their adjacent ends and capacitively coupled together at their other adjacent ends, and a utilization circuit inductively coupled to said output circuit.

2. A frequency doubler comprising an electron discharge device having anode, cathode, and grid electrodes, means for maintaining said cathode above ground potential, a, tuned input circuit connected between said grid and cathode electrodes tuned to a predetermined frequency, a source of radio frequency energy coupled to said input circuit, and a tuned output circuit connected between said anode and cathode and tuned to a frequency twice that of said input circuit, said tuned output circuit comprising a tuning inductance in the form of a pair of parallel conductors, means for varying the tuning of said output circuit, means for making said pair of conductors symmetrical with respect to ground, and a utilization circuit inductively coupled to said output circuit.

3. In combination, an electron discharge device having anode, cathode and grid electrodes, means for maintaining said cathode above ground potential, a tuned input circuit connected between said grid and cathode electrodes, a source of radio frequency energy coupled to said input circuit, and a tuned output circuit connected between said anode and cathode, said tuned output circuit comprising a tuning inductance in the form of a pair of parallel conductors, an air condenser bridged across one end of said conductors for varying the inductance of said pair of parallel conductors, and an air condenser coupling one plate of said rst air condenser to ground for making said pair oi conductors symmetrical with respect to ground.

4. In., combination, an electron discharge device having anode, cathode and grid electrodes, a tuned input circuit connected between said grid and cathode, a condenser connected across the legs of said cathode for maintaining both sides thereof at the same radio frequency potential, a heating source for said ilament, leads connecting the iegs oi said cathode to said source, and a coil located between each of the legs of said cathode and its associated lead for controlling regeneration, a condenser for varying the inductance of at least one of said coils, a resistance connected across said leads, and a connection from a point intermediate the ends of said resistance to ground, a tuned output circuit comprising a pair of lecher wires between said anode and cathode, and a utilization circuit including another pair of lecher wires coupled to the lecher wires of said tuned output circuit.

5. A combination in accordance With claim 4, characterized in this that said electron discharge device is a frequency multiplier and said utilization circuit is a pair of push-pull connected power amplier electron discharge devices.

6. In a sho-rt wave transmitter circuit, a pair of push-pull connected electron discharge devices each having anode, cathode and grid electrodes, the corresponding electrodes of said devices being coupled together, a tuned input circuit connected between said grids and a tuned output circuit connected between said anodes', each of said tuned circuits comprising a pair of lecher wires, a neutralizing condenser connected between the anode of each device and the grid ofthe associated de'- vice, means for maintaining the cathode of each device above ground potential, a connection from a point in each tuned circuit symmetrically dis posed with respect to the lecher wires therein to the cathodes, and means for biasing said grids negative and said anodes positive with respect to said cathodes.

'7. In a short wave transmitter circuit, a pair of push-pull connected electron `discharge devices each having anode, cathode and grid electrodes, the corresponding electrodes of said devices being coupled together, a tuned input circuit connected between said grids and atuned output circuit connected between said anodes, each of said tuned circuits comprising a pair of lecher wires, a neutralizing condenser connected between the anode of each device and the grid of the associated device, means for maintaining the cathode of each device above ground potential, a connection from a point in each tuned circuit symmetrically disposed with respect to the lecher wires therein to the cathodes, means for biasing said grids negative and said anodes positive with respect to said cathodes, another similarly connected pair of push-pull coupled electron discharge devices, and a pair of lecher wires inductively coupling the tuned output circuit of said rst push-pull circuit with the tuned input circuit of said last push-pull circuit.

8. In a high frequency communication system, an electron discharge device having a high fre quency output circuit and coupled thereto a circuit tuned to an ultra high frequency, said tuned circuit comprising a pair of lecher Wires and a variable air condenser bridging said lecher wires for tuning said circuit, said lecher wires being conductively short circuited at one of their adjacent ends and bridged by said air condenser at the other of said adjacent ends, whereby with change in temperature there is a minimum change in the electrical constants of said tuned circuit.

9. In combination in an ultra high frequency circuit, an electron discharge device having anode, cathode and grid electrodes, means for maintaining said cathode above ground radio frequency potential, a tuned input circuit connected between said grid and cathode electrodes, a source of radio frequency energy coupled to said input circuit, and a tuned output circuit comprising a pair of lecher wires conductively connected together at one of their adjacent ends and capacitively coupled together at their other adjacent ends, a connection including an inductance coil in series with a source of potential eX- tending from said cathode to those adjacent ends of said lecher wires which are conductively connected together, and a connection from said anode to the other ends of said lecher wires.

10. In combination in an `ultra high frequency circuit, an electron discharge device having anode, cathode and grid electrodes, means for maintaining said cathode above ground radio frequency potential, a tuned input circuit connected between said grid and cathode electrodes comprising a coil and a condenser in parallel with said coil, a source of radio frequency energy coupled to said input circuit, and a tuned output circuit comprising a pair of lecher wires conductively connected together at one of their adjacent ends and capacitively coupled together at their other adjacent ends, a connection including an inductance coil in series with a source of potential extending from said cathode to those adjacent ends of said lecher wires which are conductively connected together, and a connection from said anode to the other ends of said lecher wires.

11. A transmitter in accordance with claim 7, including a source of high frequency energy coupied to said tuned input circuit of said first pushpull circuit, and means for both frequency and amplitude modulating said transmitter connected to the tuned output circuit of said last push-pull circuit.

12. In a short wave transmitter, a single ended master oscillator comprising an electron discharge device having anode, cathode and grid electrodes, a tuned input circuit comprising a quarter wave length concentric frequency control line coupled between said grid and cathode electrodes, an output circuit for said oscillator, a frequency doubler comprising an electron discharge device also having anode, cathode and grid electrodes, a tuned input circuit connected between said last grid and cathode and coupled to the output circuit of said oscillator, an output circuit tuned to twice the frequency of said oscillator coupled between the anode and cathode electrodes of said frequency doubler, said last circuit comprising a pair of lecher wires conductively coupled together at one of their adjacent ends and capacitively coupled together at their other adjacent ends, and an electron discharge device amplifier having an input circuit coupled to said lecher wires, said input circuit of said amplifier also comprising a pair of similarly arranged lecher Wires, a utilization circuit coupled to said amplifier, an-d means for maintaining the cath- `odes of said oscillator, frequency doubler and amplifier above ground radio frequency potential.

13. A frequency multiplier comprising an electron discharge device having anode', cathode and grid electrodes, means for maintaining said cathode above ground potential, a tuned input circuit connected between said grid and cathode electrodes tuned to a predetermined frequency, a source of radio frequency energy coupled to said input circuit, and a tuned output circuit connected between said anode and cathode and tuned to a frequency which is a multiple of that of said input circuit, said tuned output circuit comprising lecher wires and a variable air condenser bridged across said lecher Wires.

14. In a high frequency communication system, a, non-oscillating electron discharge device having a high frequency input circuit and coupled thereto a circuit tuned to an ultra high frequency, said tuned circuit comprising a pair of lecher wires and a variable air condenser bridging said lecher wires for tuning said circuit, said lecher Wires being conductively short circuited at one of their adjacent ends and bridged by said air condenser at the other of said adjacent ends, whereby with change in temperature there is a minimum change in the electrical constants of said tuned circuit.

FRED H. KROGER.

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