US1669189A - Wtred-radio broadcasting system - Google Patents

Description

Filed may. 1927 F @emencs R. D. DUNCAN, JR

VIIRED RADIO BROADCASTING SYSTEM Mrealhdz'a-mmtdn9 May 8, 1928,

J. Ilz;

amig@ BBERr/M wfg-ed Opemng ZS e wmehcs i lNfg Patented May 8, 1928.

UNITED STATES PATENT OFFICE.

ROBERT D. DUNCAN, JR., 0F EAST ORANGE, NEW JERSEY, .ASSIGNOR T0 WIRED RADIO, INC., 0F NEW YORK, N. Y., A CORPORATION 0F DELAWARE.

WIRED-RADIO BROADCASTING SYSTEM.

Application filed May 7, 1927. Serial No. 189,691.

My invention relates broadly to the broadcasting of high frequency signaling currents over line wire systems and more particularly to a broadcastin system employing power lines as a guide or the high frequency currents.

One of the objects of my invention is to provide a method of altering the natural frequency of distribution transformers in a power line system foi` facilitating the transmission of high frequency currents to wired radio receivers in the homes of lighting customers.

Another object of my invention is to provide means for obtaining uniform attenuation of the high frequency energy over a power line distribution system by correcting in a graduated manner the different distribution transformers between the power generation station and the receivers of lighting customers for the eicient operation of wired radio receivers at various points in the system.

M invention will be more fully understoo from the following specification by reference to the accompanying drawings, wherein:

Figure 1 shows diagrammatically a power line distribution system indicating the arrangement therein of power transformers, the lighting load and the wired radio receiver for installation in the home of a lighting customer; Fig. 2 shows a set of typical characteristic curves for a number of power transformers in a wired radio broadcasting system; Fig. 3 shows diagrammatically the improved clrcuit arrangements of my invention; and Fig. 4 illustrates the characteristic curves obtainable in the improved system of my invention.

In a wired radio broadcasting system wherein high frequency currents are superimposed upon an electric power distribution system or transmission line, the high frequency power is usually introduced into the system at a point adjacent the power substation, from which point the current Hows over the primary feeders, through the distribution transformers and over the low voltage secondary leads to the wired radio receiver in the home of the subscriber. The feeders extending from the substation are generally polyphase, with the distribution transformers connected between each of the phases. The usual transformers are of different sizes, depending upon the load conditions, and may range from 0.5 to 50 kva.; furthermore, in their distribution along the feeder no particular regularity in size is met; for example, a 5 kva. transformer may be followed by a 25 kva. transformer, in turn followed by a 15 kva. unit, etc.

Referring to Fig. 1, there is shown a typical primary feeder A-A, B--B, supplying two transformers T1 and T2, to the low voltage secondaries of which are connected the light load l, and single wired radio receivers represented in their entirety by the numeral 2. It will be noted that transformers T1 and T2 may be separated by only a few, or by several hundred or by several thousand feet, and that the low voltage secondary lines actually extend some distance from the transformer before connected lights are met, all of such variations depending upon the line conditions.

Referring now to Figs. 1 and 2, in the former the high frequency currents are traversing conductors, A-A, B-B, and will establish a voltage between points A-B. Now experiment has shown that viewed from the primary or high voltage winding, at the wired radio frequencies, a transformer will have a varying impedance which with increasing frequency will increase, attain a maximum value, and then decrease. The manner of variation is shown in Fig. 2, where T1, T2, T3, are impedance curves for transformers T1, T2, T3. The maximum impedance occurs at the natural frequency of the transformer. For example, a certain 10 kva. transformer had a natural frequency of 37.5 kilocycles at which the impedance was in the neighorhood of 25,000 ohms, decreasing to approximately 3000 ohms for lower and higher frequencies.

It is to be expected, therefore, that for frequencies in the proximity of the natural frequency the behavior of the transformer will be erratic. Since in wired radio broadcasting it is necessary to consider bands of frequencies instead of single frequencies, and as pointed out previously, the number, method of distribution, and size of the transformers scattered along the feeder may vary greatly, it is obvious that for certain frequencies greater transmitting powers will be required than for others, or for the same transmitting power more energy will get through on some frequencies than on others, a feature which leads to distortion of the received signal unless corrected.

Experiment has revealed, however, the important fact that substantially regardless of the type and size of the transformer under the normal load conditions, the natural frequency will be somewhere in the range 25 to 45 kilocycles, indicated by Af in Fig. 2. It is also the case, that this particular range of frequencies lies directly in the range which must be used for wired radio broadcasting. By my present invention I provide a way of altering the natural frequency of distribution transformers so as to correct for their erratic behavior, which for a given set of feeders may be done in a aduated manner, thereby obtaining a uniorm energy attenuation over the feeder for the entire band of frequencies usable in wired radio broadcasting.

Reference is made to Fig. 3 which is in general similar to Fig. 1, but in addition shows condensers 3 and 4 connected in parallel with the primary windings of transformers T1 and T2, res ectively. I'Vith properly chosen values o capacities condensers 3, 4, the natural frequencies of transformers may be made substantially the same and reduced to lie without the wired radio range. IVth this connection the input impedances of the different transformers may be made to have maximum values at substantially the same frequency without the wired radio range, and to have substantially the same and uniformly varying impedance for all wired radio frequencies. This condition is represented in Fig. 4. A greatly improved transmission system from the high frequency standpoint is thus obtained. From the low frequency power standpoint, the presence of condensers on the lines acts to compensate for the lagging power factor normally existing, thereby increasing the efficiency of power transmission.

It is to be noted that condensers 3, 4, do not function as' by-passing units but serve to alter the impedance of the transformer as a whole. By the arrangement of correcting circuits for various power transformers, carrier currents may be more efficiently distributed over a power network of a city and the subscribers homes or lighting customers more adequately supplied with the broadcast programs. By graduating the impedance of the several transformers in the system the high frequency energy may be equalized throughout the system so that the volume of the reproduced signaling energy may be rendered more uniform to the various subscribers over a vast area.

While I have described my invention in one of its preferred embodiments, I desire that it be understood that modifications may be made but that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A wired radio system com rising a power transmission line arrange to have high frequency carrier currents impressed thereon, power transformers, each including primary and secondary windings, with the primary windings thereof connected with said power transmission line, and means for modifying the characteristics of each of said primary windings for offering substantially uniform impedances with respect to the transmission of wired radio frequency currents. f

2. A wired radio system comprising a power transmission line arranged to have igh frequency carrier currents impressed thereon, power transformers, each including primary and secondary windings, with the primary windings thereof connected with said power transmission line, and means oonnected in shunt with said rimary windings for altering the natural requency of sald windings and effecting uniform distribution of high frequency signaling ener in the secondary windings of said trans ormers.

3. A wired radio system comprising a ower transmission line arranged to have igh frequency carrier currents impressed thereon, a plurality of power trans ormers each having primary and secondary windings, with the primary windings thereof each having their impedances equalized for a selected band of signaling frequencies for obtaining a uniform energy attenuation over the transmission line for the entire band of wired radio frequencies impressed thereon.

4. A wired radio system comprising a power transmission line arranged to have high frequency carrier currents impressed thereon, a plurality of power transformers, each having primary and secondar windings, separate feeders connected with said secondary windings, and condensers of selected capacity values inde endently connected in shunt with said primary windings for equalizing the natural frequencies of said transformers and effectin uniform energy attenuation over said fee ers for selected bands of frequencies.

5. A wired radio system comprising a nasales 3 power transmission line arranged to have high frequency carrier currents impressed thereon, a plurality of power transformers, each having primary and secondar wind- 5 ings, separate feeders connected with said secondary windings, and condensers of selected capacity values independently connected in shunt with said primary windings for equalizing the natural frequencies of said transformers and effecting uniform 10 energy attenuation over said power transmission line.

In testimony whereof I af'x my signature.

ROBERT D. DUNCAN, Jn.

Images