US1897312A - Radio tuning method - Google Patents

Description

Feb. 14, 1933. LANGLEY 1,897,312

RADIO TUNING METHOD Filed Feb. 11, 1929 M" I W Hill min m mg INVENTOR,

A TTORNEYS.

Patented Feb. 14, 1933 I U A STATES PATENT OPE-WE ItALIH H. LANGLE Y OF CINCINNATI, OHIO, ASSIGNOR TO THE CROSLEY ERADIO CORPORATION, OF CINCINNATI, OHIO, A. CORPORATION OF OHIO ,,,Mm TUNING METHOD Application filedFeoruary 11, 1929. Serial No. 339,073.

This invention has to do with methods for tuning radio frequency 1 circuits over the broadcast range-and more p'articularly with amethod'which produces results superior to '5 thoseobtained in the usual arrangement.

One object of my invention is to produce a system of tuned circuits which will cover the broadcast ='range of frequencies and yet is materially less expensive than the usual arrangement.

Another object of my invention is to produce an arrangement which will increase the sensitivity on the low frequency portion of the range and at the same time materially increase the selectivity on the high frequency portion of the range. I

A further advantage of the invention which results from those just mentioned is that it produces a considerably greater degree of uni- 29 formity of both the selectivity and amplification than can be obtained in the usual arrangement.

A still further object of the invention is to materially decrease the difficulty of keeping '25 the amplifying system free from oscillations,

thus avoiding the provision of means of neutralization for the system.

A. still further advantage of the invention is that it gives a 360 scale on the tuning cona) trol, instead of the usual 180 degrees, and in addition makes the scale divisions very much more uniform in size when the indicator is calibrated in frequencies or by broadcast channels.

In the usual tuned radio frequency broadcast receiver, a single condenser is used to tune the grid circuit of each of the radio frequency amplifying tubes throughout the broadcast range or from 550 k.c. to 1500 k.c.

40 This has the disadvantage that the primary of the coupling transformer, if it is made sufficiently large to give good amplification at low frequencies, will result in oscillation at the higher frequencies. Since this oscillation must be avoided, the primaries are not made very large and the sensitivity of broadcast receivers is therefore many times as good at the high frequencies as it is at the low, and the selectivity is much better at the low frequencies than at the high frequencies.

The stabilizing means or neutralization in such a receiver must be sufficient to prevent oscillations with the particular primary used, the size of which is a compromise at the best. Several electrical methods have been proposed for increasing the uniformity of the selectivity of broadcast receivers throughout the range, but while these approach'the de sired results, they are inherently more expensive than the simple arrangement of my invention.

A variable air condenser, having semi-circular rotor plates can be rotated continuously if the stops are removed. Starting at a point Where the rotor plates are not meshed with the stator plates, the first 180 'of rotation (in either direction) carries the condenser from a condition of minimum capacity to a condition of maximum capacity. The next 180 of rotation in the same direction takes the condenser from its maximum capacity back to its minimum capacity. If, at the point'betweenthe first 180of rotation and the second' 180 of rotation, the inductance of the associated secondary coil could be appropriately reduced, this will result in lessening the inductance of thetransformer at thehigher frequencies when the capacity of the con densers is greatest, thus eliminating the undesirable oscillation and permitting the use of primaries of sufficient turns to give proper amplification at low-.frequencies' The secondaries of the interstage transformer are arrangedivith atap at each appropriate. point which is brought out to a centact,"which is grounded by a switching mechanism driven by the tuning condenser (I 4.. J. L! anov actuated attne point beta son the nrst and second half of the 360 rotation.

in the drawing:

Figure 1 is a diagram illustrating in simple form the arrangement of radio frequency z' ainmifving circuits of a broadcast receiver.

' eflis a persnective de" .111 illustrab "one type of switch fincchanism.

gure 3 is a view of a condenser gang illu ating an arrangement of'my invention, partially in diagram.

I have indicated the inte'rstage coupling transformers at 1, 2, and 8, and the tuning the end 10a, during half of its revolution, but Wlll be out of engagement durmgtho remainder of its revolution.

The condensers used in such an arrangement may be of approximately one. thlrdthecapacity that is required to tune through thebroadcast range when aqsi'ngle coil is used. a I

The arrangement will be 'suchthat with the condenser at maximum capacity, and the coil at'fuil inductance ineach stage of amplification, the tuning will be at approximately 550 kilocycles.- With the capacity at the minimum and the: inductance: at the maximum,-thetuning-will beto around 900 kilo-- cycles; =With the: condenserati the maximum capacity and the inductance at approximately half-,thel tuning-will-still? remain at approximately. 900; kiloeyeles, and finally with themapacity 2 atthe minimum and the inducta'nce'at approximatclynhalf, the tuning will he aIFISOQEkIIOCYClQS. 1" ,n:

r The amplification-pr sensitivity at the lower endv of the range, will I be quite satisfactory, the stability and selectivity at the higher end ofthe range willbeexcellent', in the arrangement shown.

-' The exact: location ofithe grounding connection on theseveral transformer secondaries; will be determined for the receivers to give the a result of? equalamplification from 550 l ncuto 1500-k.-c., without danger of serious oscillations; It shouldralsobe noted that, a'betterratio of inductance to' capacity is: maintained-in the upper range, thus providing; fonbetter; selectivity; over this range, than is practicalpin receivers in which the transformers arethe same at all, times It is apparent that. the mechanical arrangement shown can be variously modified to accomplish the results set forth.

Having thus described an embodiment of my invention, andset forth the advantages inherent therein, what I claim as new and desire to secure by Letters Patentis:

1. In a broadcast receiver, aseries of amplifying stages for radiofrequency, transformers coupling said stages, said stages having ground connections, tuning (condensers for said stages operated from a, common shaft, and means mechanically: operated with the movement of the condenser rotors for grounding a portion of the secondaries of the transformers, said means comprising a portion of said shaft'forming a switch portion, cut away over half its circumference, and brushes bearing on said shaft.

2. In a radio receiver, a vacuum tube circuit including a ground connection and an input transformer, and a tuning condenser, and means operated with the condenser rotor for grounding a portion of the transformer secondary, said means comprising a portion ofsaid shaft forming a switch portion, cut away over half its circumference, and brushes bearing on said shaft;

3. Ina radio receiver, a plurality of vacuum tube circuits each comprising a tapped input transformer and a tuning condenser, the condensers for the several circuits operated-by a common rotor shaft, an extension on said shaft to-serve as a contact drum, said drumgcut away in part to provide a non contact portion, and aplurality of brushes connectedto. thetaps of the several transformers respectively, and; arranged to contact, said :drum;

.. RALPHv H. LANGLEY.

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