US2018370A - High frequency circuit arrangement - Google Patents

Description

F. c. LUNNON 2,018,370

HIGH FREQUENCY CIRCUIT ARRANGEMENT Filed Jan. 26, 1951 3 Sheets-Sheet 1 Oct. 22, 1935.

INVENTOR FREDERIQ CHARL s LUNNON ATTORNEY Oct. 22, 1935. F. c. LUNNON HIGH FREQUENCY CIRCUIT ARRANGEMENT 3 Sheets-Sheet 2" Filed Jan. 26, 1951 II I INVENTOR FREDERIC CHARLES LUNNQN BY g arr/W ATTORNEY Oct. 22, 1935- F. c. LUNNON HIGH FREQUENCY CIRCUIT ARRANGEMENT Filed Jan. 26, 1931 3 SheetsaSheet 3 x k K k a: :5 A

INVENTOR FREDEPJ CHARLES LUNNON BY 4 ATTORNEY Patented Oct. 22, 1935 UNITED STATES PATENT OFFICE 2,018,370 HIGH FREQUENCY CIRCUIT ARRANGEMENT Application January 26, 1931, Serial No. 511,281 In Great Britain February 19, 1930 2 Claims. (Cl. 250-17) voltage to a following circuit while at the same time said portion of the circuit must be able to be tuned over a relatively large wave length range.

Figure 1 of the drawings accompanying the specification shows a well known circuit in which a master oscillator comprising a valve V1 is coupled to a power amplifier comprising a valve V2. The output circuit of the valve V1 comprises a tuned circuit LC the inductance L of which is tapped .at two points indicated at B and A, the tapping B being led to the grid of the power amplifier valve V2 through the usual blocking condenser 2 while the tapping A leads back to the common cathode connection.

As will be obvious, the tapping B determines the driving voltage impressed on the grid of the amplifying stage V2 while the tapping A determines the reaction adjustment of the oscillator. The inductance L thus constitutes .an inductance potentiometer and, until the ratio C/L of the master oscillator tuned circuit becomes too great for eflicient oscillation, the wave length of this circuit may be adjusted by means of the variable condenser C without-disturbing either the reaction adjustment or the intensity of the driving voltage impressed on the magnifier valve. The working range, however, imposed by this limit is somewhat narrow and if it be attempted to extend this range by altering the value of the inductance L obviously re-adjustment of the tapping points A and B becomes necessary.

According to the present invention, transfer of voltage from a tuned circuit is efiected .by tapping said voltage from .a tapped condenser or from points between a plurality of series condensers, said tapped condenser, or series condensers being connected across said tuned circuit so as to constitute a condenser potentiometer the arrangement being such that both the inductance and the capacity in said tuned circuit may be varied as desired substantially without affecting the adjustment or adjustments which determine the voltage transferred.

In the accompanying drawings, which are given mainly in order to illustrate the present invention,

Figure 1 illustrates a known arrangement of a master oscillator followed by an amplifier,

Figure 2 illustrates the present invention applied to the arrangement shown in Figure 1,

Figure 3 illustrates the present invention ap- 5:

plied to a capacity neutralized circuit,

Figure 4 illustrates a known circuit utilizing antiparasitic devices for the prevention of oscillations,

Figure 5 illustrates the present invention ap- 10 plied to a circuit such as shown in Figure 4, and,

Figures 6, '7 and 8 illustrate embodiments of the invention utilizing different capacity potentiometers, similar to those shown in Figures 2, 3 and 5.

Figure 2 of the accompanying drawings illus- 15 trates the present invention as applied to an arrangement of the kind shown in Figure 1. As will be seen, Figure 2 differs from Figure 1 in that the tuned circuit LC is shunted by three fixed condensers K in series with one another (obviously :0 an equivalent tapped condenser may be substituted for the three series condensers), and the points B and A are connected not to the inductance L in the tuned circuit but to the tapped condenser or condensers. To put the matter in 95 another way, the accompanying Figure 2 difiers from Figure 1 of the specification in that voltage is transferred from the tuned circuit LG by means of a condenser potentiometer connected across said circuit.

Figure 3 of the accompanying drawings shows the invention as applied to a capacity neutralized or so-called neutrodyne circuit. This circuit comprises a valve V2 whose output circuit contains a tuned circuit LC, capacity neutralization 85 being obtained by means of the usual neutrodyne condenser NK. In applying the present invention to this circuit, connection to a subsequent amplifier stage V3 and connection from the output circuit of the valve V2 back to the cathode 40 thereof, are established from tapping points 13' and A upon the condenser potentiometer KKK which is shunted across the tuned circuit CL. As will be seen in this arrangement, the neutrodyne balance of the amplifier stage V2 and the 4.5 intensity of the driving voltage impressed on the grid of the following stage. V3 may be adjusted once for all and need not be disturbed, while both the condenser C and the inductance L may be varied for purposes of tuning. 50

An incidental advantage of the present invention lies in the fact that it facilitates the provision of eifective means for preventing parasitic oscillations.

Figure 4 01' the drawings shows a well known circuit arrangement in which anti-parasitic devices R1 and R2 areinsertecl in the grid andplate leads of a valve V5. The path for parasitic oscillations in this circuit is indicated by chain lines and, as will be seen, this path includes (apart from the inductances of the various leads) three'inductive portions which are marked in the figure as [1 l2 and la; the oscillation in this parasitic path will be determined mainly by the grid anode capacity of the valve V5 and the inductances l1 l2 and Is. It will be appreciated that when. the tuning condensers C1, C2, are broughtto a very low valuation, the parasitic oscillation frequency may approach so closely to the fundamental frequency of the master oscillator and the magnifier tuning V circuit that the damping devices Brand; R2 induce considerable losses as respects the working frequency.

When the present invention'is applied to this circuit so as to' transform it into the: circuit arrangement shown in the accompanying Figure'5, the path for: possible parasitic oscillation passes (as is indicated .by the closed chain line) through the potentiometers consisting of the condenser elements KKK and KIKIKI so that,v while the grid-anode capacity of the amplifier valve remains as a factor in controlling the parasitic frequency, the inductances |l|2|3 are no longer in the path of the parasitic oscillations but are !-e V placed in that path by condensers, and the only inductance in the circuit is stray inductance due to leads and so forth. The parasitic fre-.- quency will therefore be so high that, in general, continuous oscillation-at this frequency will. not occur. In exceptional cases where damping devices R1 and R2 are still necessary, they may be ei fectively employed without any substantial loss occurring on the fundamental wave length. 40

The accompanying Figures 6, 7 and 8 differ The wave length of out the present invention are preferably consti- 7 from'Figures 2, 3 and 5 respectively, only in that tuted by mica dielectric condensers consisting. of a large number of elements in series, said elements beingbrought out by suitable connections to provide tapping points.

Having thus described my invention claim what I l. The combination with an electron discharge 7 having an output circuit, and another electron discharge device having an input circuit,

of a condenser potentiometer comprising four serially connected condensers for coupling, said input and output circuits together, and individual connections from said output circuit to tap points onsaid potentiometer between the first and second condensers and third and fourth condensers; 2Q

respectively, and a connection from said input circuit to a tap point on said potentiometer between the second and third condensers. 2. The combination with an electron discharge device having a tunable output circuit comprising. Q:

a variable inductance and a condenser in parallel, and another electron discharge device having an input circuit, 06 a condenser potentiometer connected across the terminals of said inductance,

said potentiometer comprising four serially con- 2 nested. unvariabic condensers: forecoupling said input and output circuits together, and individual connections from said output and input circuits to diffierent points on said condensers.

FREDERICK CHARLES LUNNON. 40

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