US1717174A - Radio receiving circuit - Google Patents

Description

June 11, 1929. N, H, SLAUGHTER 1.7177174 mmo macmvme cmcpm Filed Sept. 6, 1924 lnrenfar: Nugemhf filaug/zfer by I A/fy.

Patented June 11, 1929.

UNITEDSTATES room 3.

mOTBIO COMPANY, INCORPORATED,

NEW YORK.

SLAUGHTER, MOUNTAIN LAKES, NEW JERSEY, ASSIGNOB TO WESTERN OF NEW YORK, N. Y., A OOBPOBA'L'I ON'OF BADIO RECEIVING OIBOU 1'1.

Application fled September This invention relates to radio receiving circuits and has .for its principal object to provide a receiving set all variable elements of which are capab e of adjustment for reception of waves of difierent lengths by means of a single control element.

Another object of this invention is to provide a receiving set adapted to be used with various aerials without changing the dial settings.

A further object is to provide in a receiving set, that the natural period of a tuned antenna circuit is not materially altered by a change in serials.

A still further object is to increase the shar ness of tuning of the circuit.

0 er objects and advantages will be apparent from the following specification and claims.

These objects are accom lished by means of a small condenser inserte between the aerial and tuned primary circuit constituting a selective element of the receiver.

Figs. 1, 2 and 3 show diagrammatically, g circuits embodying the invention inwhic corresponding parts are designated by the same reference numerals.

In all figuresi condenser 1 is-interposed between the aeria andprimary circuit 2 which may be tuned byvariable condenser 16. The

maximum capacity of the condenser 1 is of the order of 75 mmf. which is small compared to that of the other condensers or elements of the circuit involving capacity to-ground capacity and condenser 16 in theprimary circuit 2, which would be I of 500 mmf. .The condenser 1 may be as small as 50 mmf. it being understood that the values herein assigned are in an apparatus suitable 40 for receiving present broadcast messages on wave lengths of from 200 to 600 meters and that the values for. other wave lengths will difier accordingly.

Asecondary circuit 3 consisting of inductance 11 andsecondary tuning condenser 12 is tuned to the same fre uency as thecircuit 2 and is loosely couple thereto either by electromagneticor electrostatic means which may be made variable, if desired, for the purpose of adjusting the coupling between thecircuits 2 and 3. v 1 As indicated on the drawings, thecondensers 12 and 16 are to be varied simultaneously by a single control element and in order to such as the aerial-v of the order 8, 1924. Serial No. 738,241.

effect this result it is needful that 'theybe shunted during the tuning operation by effective capacities of equal value. Thecondense rs 12 and 16 may in general, be of any variable type each being identical in design with the 0 er.

Various means of con ling the rimary and secondary circuits are s own in I igs. 1 2 and 3. In Fig. 1, a. series ca ificity coupling is obtained b condenser 7 w 'ch is preferably variable. 11 Fig. 2, a shunt ca acity couphng is shown by means of con enser 8 betweenprimary circuit 2 andsecondary circuit 3. In Fig. 3, primary circuit 2'is cou led to Isecondary circuit 3 by receivin trans ormer 9 which may be made adjustab e for varying the coupling. Any other means of coupling the circuits may from the spirit of the invention.

Avacuum tube detector 4, provided with the usual stopping condenser shunted by a high resistance in the grid circuit, is connected across thecircuit 3. The anode cirbe used without departingcuit 5 contains a telephone receiver 6 which typifies any desired receiving apparatus.

A smalladjustable condenser 10 is connected in parallel to the secondary tuning condenser. that the combined capacity ofcondenser 10, inputcapacity ofvacuurn tube 4, and dis tributedcapacity of the secondary coil 11 and the wiring 1s of the order of 50 mi.

A single or plural stage am lifier may be inserted in tandem betweent e tube 4 andreceiver 5 in any one of. several well known manners, in which case the input capacity of the amplifier is taken into account in the same manner as that of the detector-when there is no amplifier.

The operation and advantages of this circuit may be explained as follows: The'primary circuit contains cagacity due to the tu'ning condenser and also ue to the aerial, operatin secon ary circuit has two capacities in arallel in a similar manner due to the secon ary tun in condenser and distributed capacity of coi s, wiring and tube. In order to permit equal variation of both primary and secondary tuning condensers so that tuningcan be efiectively accomplished by a single control without redesigning for each sli htly difierent aerial, the efiective values of the capacities in shunt must be made by varying them The,condenser 10 is adjusted so.

equal. This was previously difiicult of accomplishment as the aerial-to-ground capacity was varied each time the set was used on different aerials and was of a large magnltude relative to the distributed capacity in the secondary circuit.

In accordance with this invention, the secondary capacity is adjusted to any desired amount by asmall condenser 10 in parallel to the tuningcondenser. This condenser is adjusted so that the combined capacity resulting from the vacuum tube wiring and condenser itself is approximately 50 mmf., an amount large enou h to permit of accurate adjustment and suficiently small so that the minimum capacity of the secondary circuit may be made as small as desired in tuning. The primary is adjusted in an analogous manner by inserting a condenser 1 of 75 mmf. maximum capacity in series with the aer1al. By varying this condenser, the effective capacity of the aerial to ground and condenser 1 in series may be made any des1red amount less than 75 mmf, the maximum capacity of condenser 1. This will be the case irrespective of the type of aerial used. 0 If this capacity is made equal to the minimum secondary capacity or about 50 mmf. the primary and secondary tuning condensers may be varied simultaneously by the same control means and the circuits will always be tuned to the same frequency.

Should the distributed capacity of the secondary circuit be 50 mmf. or greater,condenser 10 may be omitted. In case this capacity should be greater than 75 mmf. condenser 1 must have a larger maximum capacity to properly balance the circuits. It should be understood that the values herein used are only examples. The actual values ofcondensers 1 and 10 must be determined in accordance with the particular ty e of receivers and the use to which it is to be put.

In practice, thesmall condenser 10 may be adjusted in the factory and both tuning con- .densers connected to the same knob and dial. The set is then connected to an aerial and maximum signal strength obtained by adjusting condenser 1. After this is once adjusted for-a given aerial, it will not thereafter need to be changed as the circuits are then of equal capacity and the single control knob will tune in all signals within the rangev of the receiver.

Condenser 1 also materially increases the sharpness of tuning of the primary circuit as the loose coupling between the aerial and primary circuit caused thereby greatly reduces the damping effect of the aerial resistance on the primary circuit.

It is known that condensers have been used in series with the aerial for purposes of tunm but the instruments and purpose are consi ered to be entirely different than as herein set forth. The condenser 1 is too small to be large that of any value in tuning and, in fact, would not vary the period of the aerial to ground circuit to any appreciable extent. Condensers such as previously used in tuning were so they could not function in accordance with this invention. They were not of sufiiciently high impedance to insure absence 'ofinteraction between the aerial and tuned primary. The tuning of the primary was affected by the size of the aerial and the sharpness of tuning was affected by the resistance of the aerial.

Although shown as applied to particular,

circuitsit is to be understood that the invention is not limited in its application to these particular circuits but only in accordance with the spirit of the invention as defined in the claims.

-What is claimed is:

1. In a radio receivingcircuit comprising an aerial and tuning means, a condenser of the order of 75mmf. interposed between said aerial and said tuning means to minimize the effect of the aerial on the tuning of the antenna circuit and a resonant circuit coupled to said tuning means having a total minimum capacity substantially e ual to the combined capacity of said aerial and said condenser. V

2. In combination, two resonant circuits, an element having capacity to ground, means for tuning both said circuits in a single operation, and a path between said element and one of said circuits including a capacity for minimizing the effect of said capacity to ground on said circuits.

3. In combination, two coupled resonant circuits, means for tunin said circuits in one operation, an element having capacity to ground connected to one of said circuits, an-

other element having material capacity connected to the other of said circuits, and supplementary means associated with the circuit having capacity to ground for equalizing the capacity of said elements whereby said circuits may be maintained in resonance at the same frequency.

4. In combination two coupled resonant circuits, means for tuning said circuits in one operation, one of said circuits including an element having material inherent capacity and the other of said circuits being adapted to be connected to any one of several elements having different material capacities,

and means to reduce the influence of saidelements of difi'erent capacities on the tuning of the connected circuit comprising an additional capacity adapted to-be included in the connection to said elements. of. difi'erent capacities.

5. In a radio receiving circuit comprising an aerial and primary and secondary tuning means, means comprising a small condenser connected across said secondary tuning means to adjust the minimum secondary capacity to a finite value and means comprising a small condenser connected between the aerial and primary tuning means to adjust the antenna capacity to the samefinite value 5 so that equal changes in the primary and secondary tuning meansv will produce equal changes in f requency of the respective circuits whereby they may be controlled by a single means.

In Witness whereof, I hereunto subscribe 10 myname this 5th day of September, A. D. 192

NUGENT H. SLAUGHTER.

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