US1738274A

US1738274A - Wave transmission means

Info

Publication number: US1738274A
Application number: US2477A
Authority: US
Inventors: Sidney E Anderson
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1925-01-15
Filing date: 1925-01-15
Publication date: 1929-12-03
Anticipated expiration: 1946-12-03

Description

Dec. 3, 1929. s. E. ANDERSON WAVE TRANSMISSION MEANS Filed Jan. 15, 1925 Patented Dec. 3, 1929 ilhlllil filil tl'l'A'l'Evd ravens" SIDNEY E. ANDERSON, F MAPLEWOOD, NEW" JERSEY, AElBIG-IME IVIISEEIE ACLEIGN- MENTS, 10 VEEEYEERN ELECTZEJIC COMPANY, INGORPURATED, OE NEW YURK, 52'.

CORPQRA'IIQH OLE NEW YORK WAVE TRANSMISSION arm-ins Application filed January is, 19535.

This invention relates to wave transmission means and particularly to frequency selective structures.

A special problem presents itself to the radio engineer, when it is desired to construct a radio receiving system to be connected to a receiving antenna which is relatively near to a transmitting antenna. This problem relates to the exclusion of waves of the transmitted frequency from the receiving set and to the protection of the receiving circuit from the excessive voltages generated in the eceiving antenna. The diiiiculties encountered become greater and the solution of the resulting problems becomes more diiiicult when the sending station transmits considerable power.

The present invention provides a frequency selective and voltage protective arrangement for guarding a receiving system against large voltages developed in its circuits and from in terference to received 5'' ,nals caused by a nearby transmitting station, and at the same time enables desired waves to be eiiiciently re ceived.

An object of the invention is to protect the circuits and apparatus of an electric wave signaling system from excessive electric stresses.

Another object is to prevent interference with the received signals.

A further object is to trap undesired waves in an electric wave signaling system.

An additional object is to cause a wave receiving conductor to function as an element of a wave filter network.

A still further object is to secure a maximum eliiciency of transmission of desired waves in a wave trapping and selecting not work.

The invention is capable of embodiment in' tion, a series clement.

Serial No. e rrr.

pedance to desired waves. Means is also provided to adjust the impedance of the series element to match the impedance of the rest of the system in order to obtain amanimum ciliciency in wave transmission.

In the drawings, Fig. 1 represents a radio receiving sy m arranged in accordance with the present invention;

Fig. 2 represents a modified form of the series element of the filter network shown between the dotted lines 1 and 2 of Fig. 1.

A circuit embodying the invention will now be described in detail. In Fig. 1, an antenna is connected to ground in series with an inductance 11 and an adjustable condenser 12. The antenna 10, in conjunction with the inductance 11 and condenser 12 forms a portion of a band filter, which includes in addi- The series element comprises a two winding transformer 13 having an adjustable condenser 14 connected to its secondary winding. The use of a two winding transformer enables the impedance of its winding to be matched tot-he impedance of the connected circuit to provide increased eliiciency in the transmission of waves. Also by a proper impedance ratio between windings, the condenser 14+. may be of convenient proportions. By means of a switch 18, the series element of the filter may be connected directly to the transformer 15 or in series with adjustable condenser 17 and inductance 16. The secondary winding of transformer 15 is provided with leads extending from its outer and middle terminals to a radio receiving system, represented by block 20, which maybe of any one of several types.

The inductance 11 is so designed and the condenser 12 is so adjusted as to form a resonant circuit tuned to the frequency of waves impressed upon the antenna 10 which it is desired to exclude from the receiving circuit 20. so tuning this portion of the antenna path, waves of the undesired frequencies are prevented from proclucing a large voltage between the outcr terminal of inductance ill and ground since this path has low impedance to these waves. Moreover, this element of the filter produces great attenuation of the undesired waves transmitted to the receiving circuit by affording a low impedance path to ground in shunt thereto.

The circuit including the secondary wind- I ing off-transformer 13 and the adjustable condenser 1 1 is also tuned to the frequency of undesired waves. This circuit, being of the parallel tuned type, has high impedance to these waves and since its impedance is reflected in I i plied to the series element 1314: of the band elimination filter as well as the other elements of the system, thereby making it unnecessary to design the apparatus associated therewith to withstand high voltages.

An advantage of the present invention in functioning as a band filter relates to the fact that not only the carrier frequency interferingwaves may be substantially completely excluded, but also the side band frequency waves'as well. The sharpness of the filter cut-off'or the slope of the sides of its characteristic curve may be increased by adding thereto additional sections such as that constituted by shunt element 11, 12 and series element 13, 14.

In operating the system, the switch 18 may normally be closed .on contact 3 so that selection of 'a desired station may be obtained without adjusting condenser 17. Increased selectivity may subsequently be obtained by shifting switch 18 to contact 4, thereby including the condenser 17 and inductance 16 in the antenna circuit whereby the latter may be tuned to the frequency of waves which it is desired to receive.

In Fig. 2, a modified form of the series element of the band elimination filter is represented. This includes an auto-transformer 13 having an adjustable contact whereby its impedance may be matched to the impedance of the remaining portions of the antenna circuit so as to obtain maximum efiiciency in the transmission of waves to the receiving set. Condenser 14 corresponds to condenser 14 of 1 and serves to enable the series element Flg.) to e tuned to the frequency of undesired waves The circuit shown in Fig. 2, when substituted for the corresponding element of Fig. 1, functions in substantially the same I manner.

What is claimed is: In a radio receiving system, the comblnation of an antenna, a seriesresonant path fwaves, in said second path, a switch for con- 'necting said serially connected inductance and capacity in said second path, and a parallel resonant circuit tuned to the frequency SIDNEY E. ANDERSON.