US2370985A - Carrier-current telegraph system - Google Patents

Description

March 6, 1945. o so 2,370,985

CARRIER-CURRENT TELEGRAPH SYS TEM Filed Aug. 13, 1943 40 fl 4 v= v ch 8 V E Y INVEW 7/.

Patented Mar. 6, 1945 'UNITED :STATES PATENT OFFICE Montford Morrison, Upper Montclair, N. J.

Application August 13, 1943, Serial No. 498.496

2 Claims.

This invention relates to carrier telegraph systems, in which the separation of the transmitted signals, at the receiving terminals, is accomplished by electrical filter circuits.

Among the objects of this invention is to provide a selection of carrier-current frequencies which are conducive to a reduction in channel interference in the receiving circuit filters; to provide a selection of carrier-current frequencies which allows the operatively successful use of smaller and simpler separation filters in the re-- ceiving circuit; and to provide a better overall quality of signal reception in carrier-current telegraph systems.

These and other objects will be obvious upon reading the specification in connection with the accompanying drawing, in which Fig. 1 shows a conventional diagram of one class of electrical filter circuit in which my invention may be embodied; Figs. 2 and 3 are curves illustrating some of the theory of the invention; and Fig. 4 is a listing of odd harmonic components, set up for easy reference. I

In theprior art, difllculty arises in the receiving circuit channels of carrier telegraph. systems from two sources of interference between the separate channel filters.

One source of interference between separationchannel filter circuits is due to the transit cur- I have discovered that interferences between the 9th tends to interfere with the 27th; and

so on.

It is American practice to use only odd harmonic components of given fundamental, in car- .rier telegraph transmission systems because of the sum-and-difierence harmonics that are senerated in the amplifier tubes; and therefore, I am giving in the present embodiment, those harmonies which are commonly used in this country, although my invention is not limited to any particular series of harmonics.

In any tuned circuit, such as a receiving circuit filter, where there is an accumulation of energy by reflection or by resonance itself, this accumulation is magnified between the fundamental andan odd harmonic due to the availability of energy in one harmonic, in such a phase relation, as tends to transfer it to a circuit of another odd harmonic frequency.

Referring to Fig. 2, where 8 represents the sine rents in the adjacent filters. Another source-of curve of energy. y. in fi er D and 9 represents interchannel interference is found where one channel is operating on an harmonic of another channel, and this may be either a higher harmonic or a sub-harmonic of the channel causing the current in filter F, it will be observed that the average current of the-3rd harmonic is, shown as a positive value, during the same half-period as the fundamental 8 has a positive value, and likethe interference, and it is this second-mentioned as i the average value of the 3rd harmonic f class of interference that the present invention eliminates.

Referring to Fig. '1. this shows a conventional telegraph carrier circuit in the most generalized the second half-period of the fundamental is negative when the fundamental has a negative value; therefore, these two circuits would, under favorable conditions, tend to exchange energy between form in which I, 2 and 3 are alternating current 40 them. Referring to Fi 3, where a second hargenerators; A, B and C comprise the corresponding station terminal apparatus on the transmission end; 4 is the transmission circuit; D, E and F are the separation filters at the receiving station terminal; and resistors I, i and I are used-46 to illustrate loads in the circuits.

If the filters D, E and F comprised perfectlymatched filter elements and had only one frequency impressed upon each, no reflections would evenly divisible one into the other, and if I desire 7 channels, I may use any? harmonics that are be-caused by the loads and However not evenly divisible one into the other. As a matis not possible to prevent some reflections from the load circuits, and because thereceivins filter elements are not perfectly matched, some reflections occur and some oscillations may exist within the filters themselves.

ter of illustration, I show that for 5 harmonics, I

prefer to use the 5th to the 13th, inclusive; for 'lharmonics, I prefer to use the 7th to the 19th.

u inclusive; for 9 harmonics, I prefer to use the):

to the 25th, inclusive; and for 11 harmonies, I prefer to use the 11th to the 31st, inclusive.

By the elimination of inter-channel interference. due to oscillations and/or reflections oc'- curring in the filters themselves, the filters embodied in my invention may be built whiohdo, in fact, have reflections in them and/or may be oscillatory in design themselves. This means that a load resistor, if and when used, may have a lower resistance than called for by the filter design to eliminate reflections and/or oscillations. This means that the filter may be made smaller and less expensive than in the case of having to provide a design employing critical, damped characteristics.

My invention ls particularly adapted to carrier telegraph channels where terminal load resistors are not used, such as employed in super-audio carrier telegraphy which commonly employs frequencies between 3,000 and 10,000 cycles.

Commensurable, as used herein, is defined as having a common measure; capable of being exactly measured by the same number, quantity, or measure; or expressible as integral multiples of some common unit." Incommensurable. as used herein, is defined "not commensurable."

While I have given in only one embodiment an adequate amount 0! direction to those skilled in the art to which my invention appertains, to make a and use same, I do not limit myself to the embodiment shown, and give the scope of my invention in the claims hereunder.

What I claim is:

l. The method 02 carrier-current telegraph transmission, which comprises transmitting carrier frequencies of a continuous sequenceof a mathematical series, said frequencies transmitted being only consecutive odd multiples of a single fundamental frequency, and each of the frequencies transmitted being indivisible evenly by any other of said frequencies transmitted.

2. In a multi-channel telegraph system, a single transmission circuit, a combination of carrier frequencies in said circuit, said frequencies being represented by a finite sequence of a Fourier series having consecutive odd terms only, and each frequency in said finite sequence being indivisible evenly with any other frequency in said finite sequence.

Mom'r'onn MORRISON.

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