US2297126A - Directional tuning indicator - Google Patents

Description

p 2 A. WIBARBER 2,297,126

DIRECTIONAL TUNING' INDICATOR Filed Jan. 26, 1939 2 Sheets-Sheet 1 Sept. 29, 1942, A. w. BARBER 2,297,126

DIRECTIONAL TUNING INDICATOR Filed Jan. 26, 1939 I 2 sneepsfisneec 2 H INVENTOR W/WM Patented Sept. 29, 1942 UNITED STAT-E S PAT E N T OFFICE DIRECTIONAL TUNING INDICATOR Alfred W. Barber, Flushing, N. Y. Application January 26, 1939, Serial No. 252,898

2 Claims.

My present invention relates to carrier wave receivers. More particularly it relates to a system for indicating correct tuning conditions in such a receiver and for indicating, when incorrectly tuned, the direction in which the receiver should be tuned to obtain correct tuning.

One object of my present invention is to provide improved tuning indicator means in tunable carrier wave receivers. Another object is to provide tuning indication means which indicate when the receiver is mistuned and in which direction it is mistuned. A particular object is toprovide a tuning indicator showing a pattern which indicates correct tuning and which moves in the same direction as the tuning control.

Before the inception of automatic volume control in radio andother tunable carrier wave receivers, tuning was accomplished, for the most part, by ear. The application of automatic volume control to receivers, however, made it diificul-t to tune correctlyby ear due to the fact that the sensitivity-ofsuch a receiver varies in passing thru a signal and thus gives a substantially constant output over a range on eitherside of resonance. This inability to tune by ear has led to various visual devices to aid in the correct tuning of a receiver. Most of these tuning aids make use of the fact that the plate and screen currents of automatic volume controlled amplifying tubes varies in accordance with their gain and hence indicate by minimum current the minimum gainor true tuning point ofthe receiver. These devices indicate by a maximum. meter deflection or similar means the correct tuning point. However, mistuning whether above or below the desired point gives the same. indication. The same result to two causes is. confusing to the senses. Also bandpass systcms are not easily tuned since there is no definite maximum response point. I propose to overcome these and other tuning difficulties.

My present invention is. of means for indi-' cating resonance and mistuning in such a way that high and low tuning is indicated and dif- 45.

ferentiated. In use this indicator has the great advantage that tuning in one direction has a different effect on the tuning indication than tuning in the other direction. The senses quickly learn to associate the corresponding effects and causes enabling more natural and easy use of tuning indicators. One way in which I carry out this directional, tuning indication is to. indicate the voltages and phases of primary means of a cathoderay tube. Various patterns are obtained and in general they may be 'so formed that they appear to rotate. By observing the proper polarity 'thru the system this rotation may be made totake place in the same direction as the rotation of thet-uning knob, adriing still further to the naturalness of the system. An additional advantage of my system is that it may be applied to band-pass systems as readily as to sharp "response systems. This al.- lows tuning variable selectivity systems in their expanded condition asaccurately as in a contracted condition. The accuracy of indication is very high making the system of advantage in such devices aswave meters or frequency monitors.

The following description-when taken in connection with the drawings will serve to point out; more specificallyhow my new tuning indicatoroperates.

In the drawings:

Fig. 1 shows a complete radio receiver embodying one form ofmyinvention.

Fig. 2 shows various-cathode ray tube patterns which may be obtained from the system shown in Fig. -1.

Fig. 3 shows a modifiedfor-m' of my-invention.

Fig. 4 shows additionalcathoderay tube pat-- terns.

Fig. 5 shows an additional form of my invention.

In Fig. l I-have showna superheterody-ne radio receiver connected to an antenna A-and-a ground G. It consists in a first detector I, anintermediate frequency amplifier 2, -a second detector 3, an audio amplifier- 4, an oscillator 5 and a. power supply rectifier 6. A cathode ray tube 1- is connected to the receiver in such a way as.

to act as my directional tuning indicator. Since the receiver is conventional and well known in the artit will only be described further in itsconnection to my tuningindicator. The tuning indicator consists in a cathode ray-- tube 1 energized by a suitablepower supply not shown, or from the regular receiver power supply. This tube may include a cathode, control grid, focusing anode and -=accelerating' anode which are not shown since they may be of conventional design. While other well known means of deflection may be used I have shown four electro-static" deflecting plates 8, 9, [0 and I1 arranged. in mutually perpendicular pairs. One plate in each pair as to and II may be grounded as shown orconnected to a suitable point of-reference potential:

and secondary of a pair of coupled circuits by Dcfl plate 8 iscormected' to Primary '2 of the last intermediate frequency transformer of the receiver. This transformer may be tuned to resonance by means of the adjustable condenser I3 or by other well known means as for instance a fixed condenser and an inductance variation of primary I2. The high or plate side of primary I2 is connected by means of lead I-I thru blocking condenser I5 to deflecting plate 8. Resistor I6 may be a high resistance of the order of a few megohms providing a reference bias to plate 8. Plate 9 is connected to secondary I1 which as in the case of primary I2 may be tuned by the adjustable condenser I8 or other well known means. Plate 9 is connected to the high side of secondary I1: by means of lead I9 and blocking condenser 20. Resistor 2| functions as resistor I6 and serves to bias plate 9 and may be of the order of a few megohms resistance.

As I have shown and described the connection of cathode ray tube 1 to coils I2 and I1 the tube will indicate by a vertical beam deflection the intermediate frequency voltage across primary I2 and by a horizontal deflection the intermediate frequency voltage across secondary I1. While this method of resonance indication is not limited to any particular type or degree of coupling between primary I2 and secondary I1 I shall describe at this point its operation for the case of less than critical magnetic coupling between these coils. The receiver is tuned by the radio frequency stage condenser 22 and the oscillator condenser 2|. As these condensers are varied in tuning in a signal the voltage across coil I2 will increase until it reaches a maximum when the radio frequency circuit is resonated to the signal and the sum or difference frequency between the oscillator and the signal frequency equals the intermediate frequency to which primary I2 and secondary I1 are tuned. This maximum primary voltage will produce a maximum vertical spot deflection on the cathode ray tube and with less than critical coupling between primary and secondary a smaller maximum horizontal deflection due to the secondary voltage. The secondary voltage will be 90 degrees out of phase with the primary voltage and hence the resulting pattern on the cathode ray tube screen will be an ellipse with its greater axis vertical a shown at d in Fig. 2. Now if oscillator 5 is tuned to a slightly lower frequency the phase and amplitude of the secondary voltage will change and the cathode ray tube pattern will rotate as shown by e of Fig. 2 due to the varying intermediate frequency. Further oscillator frequency decrease will produce patterns and g and finally a single spot. Similarly if the oscillator is tuned higher than resonance the pattern will rotate in the opposite direction as shown at c, b, and a. If the control knob 22' of condensers 2| and 22 is geared to produce a decrease in frequency for a clockwise rotation the tube pattern will rotate in the direction of the control rotation.

I have found this tuning indicator to be Very sensitive it being possible to tune to within plus or minus cycles of resonance using an intermediate frequency of 500 kilocycles and a cathode ray tube pattern one inch high.

In Fig. 3 I have shown a modification of Fig. 1 in which the coupling between, primary I2 and the secondary I1 of the intermediate frequency transformer is variable as indicated by the arrow 21 thru the two coils. This may be taken to be a portion of a variable selectivity carrier wave receiver and other means than the manual coupling control may be used to vary the selectivity such as automatically controlled regenerative or degenerative feedback. The cathode ray tube is connected in the same manner to primary I2 and secondary I1 as in Fig. 1 and corresponding members have been used to indicate corresponding parts.

Fig. 4 shows'patterns which are produced on the cathode ray tube screen by the system of Fig. 3 with the coupling between primary I2 and secondary I1 substantially greater than critical as may be used to produce a broad band response. At resonance a short horizontal line 2' indicates that the received frequency is equal to the mean response or dip point of the combined primary and secondary response. As the tuning is varied from this mean point the pattern shifts toward h or depending on whether the tuning is higher Fig. 4. In varying the coupling between primary- I2. and secondary I1 the tuning indicator patterns assume all intermediate forms between those of Fig. 2 and those of Fig. 4.

Thus my tuning indicator indicates whether tuning is high or low and functions for all practical values of intercircuit coupling. It is particuiarly useful in the overcoupled cases as shown in Fig. 4 since conventional tuning indicators become inadequate in flat-topped or double peaked response systems. This tuning indicator may be applied to tuned radio frequency circuits since varying the secondary circuit tuning gives an indication quite similar to that obtained by varying the input frequency.

In Fig. 3 I have shown a switch 26 which may be used to short circuit condenser 20 thus applying the automatic volume control or detector products to plate 9 along with the radio or intermediate frequency voltage. This causes the pattern to move to the left as resonance is passed thru and adds an additional characteristic to the tuning indication.

In Fig. 5 I have shown my directional tuning indicator applied to a triple circuit transformer. A third tuned circuit consisting of coil 24 tuned by condenser 25 is coupled to primary I2 and to secondary I1 and is used to improve the selectivity characteristics of. the transformer. My

tuning indicator is shown connected by leads I4 and I9 across primary I2 and secondary I1 but it may be connected to any pair of these circuits.

It will be evident to one skilled in the art how these circuits and modifications thereof may be applied to wavemeter and similar frequency indicating circuits. 7

While I have shown and described only a few systems whereby my invention may be carried out many modifications are possible within the spirit and scope of the invention as set forth in the appended claims.

What I claim is:

1. In a tunable carrier wave receiver the combination of at least two coupled circuits, a cathode ray tube including four electrostatic beam deflecting plates disposed in mutually perpendicular pairs, a thermionic vacuum tube amplifier connected to one of said circuits, capacitative coupling means connected between the last said circult and one of .said deflecting plates, 9. thermionic vacuum tube diode rectifier connected to the other of said coupled circuits, capacitative coupling means connected between the last said circuit and a deflecting plate perpendicular to the last said plate, and a shorting switch connected across the last said capacitative means.

2. In a tunable carrier wave receiver the combination of at least two coupled circuits, a cathode ray tube including four electrostatic beam deflecting plates disposed in mutually perpendicucircuit and one of said deflecting plates, a thermionic vacuum tube diode rectifier connected to the other of said coupled circuits, capacitative coupling means connected between the last said circuit and a deflecting plate perpendicular to the last said plate, and a conductive connection to said diode for indicating by means of the last said plate the sum of all unrectified voltages applied to said diode plus all rectified voltages lar pairs, a thermionic vacuum tube amplifier 10 generated by said diode.

connected to one of said circuits, capacitative coupling means connected between the last said ALFRED W. BARBER.

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