US2138134A

US2138134A - Short wave signaling

Info

Publication number: US2138134A
Application number: US73404A
Authority: US
Inventors: Harold H Beverage; Philip S Carter; Gilbert S Wickizer
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1936-04-09
Filing date: 1936-04-09
Publication date: 1938-11-29
Anticipated expiration: 1955-11-29

Description

NOV. 29, 1933. H, BEVERAGE ET AL 2,33%,134

SHORT WAVE S I GNALING Filed April 9, 1936 4 Sheets-Shet 1 INVENTOR HAROLD H. BEVERA6E,PHILIP s. CARTER AND GILTSWICKIZER ATTO R N EY Nov. 29, 1938. H. H. BEVERAGE ET AL 2,133,134

SHORT WAVE SIGNALING Filed April 9, 1956 4 Sheets-Sheet 2 REFLECTOR INVENTORS HARULD H.BEVERAGE,PHH.IP $.CARTER u TS.WlCKlZER )wv-Q ATTORNEY L/ N BY} A 1% 1 350115 75') AFHWA 7145 Nov 29, 1938.

H. H. BEVERAGE ET AL 9 9 SHORT WAVE SIGNALING Filed April 9, 1936 4 Sheets-Sheet 3 REFLECTORS ///6/1 FRfQUfNCY APPARATUS TNVENTORS HAW/LU H. BEVERAGE, PHILIP SCARTER AND ILBfP S-WICKIZER w, f 6? 5 mm ATTORNEY ham 29 H. BEVERAGE ET AL 2,338,134

SHORT WAVE SIGNALING Patented Nov. 29, 1938 pN-irso ST PATET; FIQE SHORT WAVE SIGNALING Application April 9, 1936, Serial No. 73,404

2 Claims.

This invention relates to the transmission and reception of ultra short radio waves within the range of optical vision. i

In a radio circuit employing ultra high frequencies for communication between two buildings, one of which, or both, is of considerable height, it has been found that the signal received at the receiving antenna will vary in amplitude as the frequency is changed. Such variation in amplitude of the received signal is caused by a change'in phase between the direct and indirect (that is, the reflected) rays received from the transmitting antenna due to the differences in the lengths of the paths traversed by these different'rays. 7

One of the objects of the present invention is to overcome the foregoing undesired variation in amplitude and phase of the received signal as the frequency is changed, and this is achieved by eliminating entirely, or materially reducing the number of the indirect or reflected rays from the transmitter to the receiver. Since the received signal is derived chiefly from the direct rays, it has been found that the reduction or elimination of radiation of energy at wide angles from the di rect path which causes reflections to occur,and also reduction or elimination of the indirect or reflected rays at the receiver, reduces or eliminates the variations in amplitude and phase in substantially the same degree. More specifically, the objects of the present invention are achieved by using directive antennas at both transmitter and receiver for eliminating or reducing the indirect rays.

It has been observed that the presence of indirect or reflected rays at the receiver not only causes an undesired amplitude variation but also a troublesome phase shift which, in the case of television signals," distorts the image. Consequently, another object is to obtain a flat response curve over an extremely wide frequency band, such as might be employed in the broadcasting of television programs when transmitting between two stations in the direct line of sight.

Although it is to be distinctly understood that the invention is not limited in scope to the precise details described hereinafter, which are given for the purposes of explanation, it is preferred that the directive antennas at the transmitter and receiver each comprise horizontal half wavelength radiators placed end to end in the'same straight line and mounted in front of reflectors, preferably copper sheet reflectors. In using such a preferred arrangement in a congested section in New York city, New York, between the fourteenth floor of one building and the eighty-fifth floor of another building, separated by a distance of about one mile, and employing a frequency in the region of 176 to 182 megacycles, satisfactory results were obtained over a band of three or four megacycles.

The following is a more detailed description of the invention, which is accompanied by drawings wherein:

Fig. 1 illustrates, in elevation, the manner in which the indirect or reflected rays from a transmitter may interferewith the direct ray received at a distant point;

' Fig. 1a is a top or plan view of the system of Fig. 1;

Figs. 2 and 3 illustrate in vector form, the relation of direct and reflected rays for two different frequencies;

Fig. 4 illustrates by way of example a preferred form of directive antenna for the transmitter, while Fig. 5 illustrates a preferred form of directive antenna for the receiver; Fig. 5a is an end view of the system of Fig. 5;

Figs. 6-10, inclusive. illustrate different antenna embodiments which may be used in the practice of the invention.

Referring to Fig. 1, there are shown two building T and R, spaced apart from one another in the direct line of sight, between which it is desired to transmit radio waves of extremely high frequencies from a transmitter A located on building T to a receiver C located on building R. Line D indicates the path of travel of the direct ray between the transmitter at A and the receiver at C, While lines I, I indicate the indirect or reflected rays between the two stations. Indirect rays I, I are in different planes and are reflected from the ground and surrounding buildings and received at the receiving station C over paths which are considerably longer than the direct path D, and thus give rise to irregularities in the response curve received at C when there are employed single antennas at the transmitting and receiving stations. With a large number of buildings B existing in the space between buildings T and R, there are almost an infinite number of surfaces at most every conceivable angle so that under these conditions a very large number of indirect rays are possible and shown, by test, to exist. Although the transmitting station A has been shown located on the lower part of building T, it will be understood that this location of the transmitting station is merely for purposes of illustration, inasmuch as this was the arrangement actually used in practice, but that such reflected rays will also exist regardless of the positions of A and C on the two buildings T and R.

Figs. 2 and 3 indicate vectorially, merely for purposes of exposition, the relation between the direct and receiving rays with change in frequency. In these figures the magnitude of the direct ray is indicated by vector D and the'magnitude and phase relations of indirect rays by the vectors I1, I2, and I3. R indicates the magnitude and phase relation of the resultant of the direct and reflected rays. An inspection :of 'ithesewfig ures shows that the reflected rays 1;, I2 and Is assume phase relations with the direct rays, depending on the length of the path difference. ;If the frequency be changed a given amount, the phase relations between the direct and reflected rays assume different values,.determin.ed. again by the lengths of the path differences. Theresultant of the various rays will thus assume a different magnitude, as shown in Fig- 3, which indicates the relation of direct and reflected raysyat'a frequency different from that of Fig. 2. In this nianner it will be observed that the response curve over a given frequency range will vary-in amplitude with variation in frequency, due to the reflected rays. The numerical values given to vector R in Figs. 2 and 3 show the relative magnitudes of the resultant voltages at the receiving antenna'for two possible combinations :of .direct and reflected rays, as the frequency ofthetransmitterfis changed.

In accordance with the ,present'inventiomthe variation in amplitude of theresponse curve is overcome by eliminating;altogether,-or materially reducing the number of indirect rays, and, inasmuch as the direct'ray-will then predominate, the response curve will-be'flatter'and thus-improved accordingly. Also, by means of the present invention, the phaserelationsofthe modulation side frequencies will notbechangecl in the radio-transmission of signals from one location-to another. This is achieved'by employing directiveantennas at both the transmitting and receiving terminal stations. These antennas arenot limited to any one particular type but should preferably be of the type which use substantially horizontal polarization. It should be understood, however, at this point that the type of directive antenna is restricted by the requirements of a flat response curve over a-wide band of frequencies.

Fig. 4 showsa preferred arrangement of directive antenna-to be used at the:transmitter comprising a pair of arms I '2, each a half wavelength ong, and separated approximately a half wave between centers. The design of the antenna of Fig. 4 is preferred mainly due to the high radiation resistance which broadens the resonance curve of the antenna. Arms I and .2 are in effect doublets, which are placed in the same general line and arranged'horizontally and slightly less than one-quarter wavelength in front of a sheet copper reflector 3, although the distance of the arms from the reflector is not critical. 'The reflector of the transmitting antenna, if desired, may be mounted a distance of several wavelengths from the building wall, thus eliminating reflections from the wall. The antenna is connected to high frequency apparatus 4, which may be either a transmitter or receivenby means of feeder wires 5 which tap on to aquarter wave U-shaped line 6, joining the adjacent ends of the arms together. By suitably choosing the proper'tapping points of line 5 on the U-shaped loop-6, the impedance of the antenna will be matched to'that of the trans mission line. The legs of the-U-shaped loop are spaced closely together to prevent undesired radiation. For supporting the antenna to the copper sheet reflector 3, there are provided

rods

1, 8 and 9 which connect the arms I, 2 and the loop 6 to the reflector at voltage nodal points. Since the arms I and 2 are each a half wavelength long, the supports 1 and 8 are respectively connected to the centers of the arms. .Similarly, since each leg of the U-shaped' loop 6 is a quarter wavelength and the overall length thereof is a half wavelength, the center point of the U will be a voltagenodal point and it is to this point that the support 9 is connected. Inasmuch as there is zero voltage at the voltage nodal point, the sup- ;ports 1, 8 and9-may comprise metallic supports or insulators, whichever is desired. Such an arrangement as that of Fig. 4, it was found, gave a satisfactory flat response curve at the receiver over a frequency width of three megacycles, using a carrier frequency of 177 megacycles.

Fig. .5 shows the preferred arrangement "of 1directive antenna to be used ,at-the receiver, also comprising two half wavelength :arms I and L2 in'the same straight line. The adjacent ends of arms I and 2 are preferably connected together by two so -called hairpin connections, or U -.shaped loops l0 and |I,,-the;legs of whichare each onequater wavelength long, as shown. This .zarrangementof loopsl-ll and H provides two high impedancelinesconnected inparalleland soldoes not affect the electrical performance of the system, besides having the advantage of giving greater mechanicalxstrengththan the-use of one U-shaped loop. Each U is .mechanically linked at a voltage nodal point to the sheet acopper reflector 3 which gives added directivity to athesystem as in Fig. 4. The arms -I and land the loops Hi and H are mounted on themeflectorfi at voltage nodalpoints, as in'Figal. "Ihefionble hairpin type of connection I0 and Lit will-be evident, is not necessarily restricted to use-cureceiving antennas ,since :such an :arrangement is equally capable of being -11s.ed on transmitting antennas.

fIf the transmitter were located :at-the top of building T and the receiver also elevated high above ground, then ,directivity in the vertical plane is preferably employed,;-and-Fig.:6 shows an antenna system :for obtaining such ;,directivity in the'vertical plane for use bothtat thetransmitter and receiver. In'Fig. 6 thereare showntwohorizontally directive antennas l2 and 13, similar in design to that of Fig. 4, both energized cophasally and so spaced apart vertically 386110 eliminate the reflected ray. The proper spacing between the two antennas l2 and 11-3, to effect elimination of reflectedrays, is shown-inFig-afia, which is a side view of .Fig. 6 with added descriptive notations. This spacing is indicated by the formula sin {b Although such spacing is effectivein eliminating One particular ray, in practioeit will befound that the spacing reduces the effect of other indirect rays arrivingat other angles. ,Theangles of the indirect rays can be calculated from..an inspectionof the response curve.

Fig. '7 illustrates. a method ,of obtaining ,di rectivity in the horizontal plane by arranging two directiveantennas in the same straightrline and energizing them cophasally. Here againthe spacing is such as to eliminate the reflectedray. It should be noted that in this case the feeder lines tap directly on the arms of the antennas at spaced points to match the impedance of the feeders. This is an alternative arrangement to that shown in Figs. 4 to 6 for connecting the high frequency apparatus to the antenna.

Fig. 8 shows another antenna system comprising two parallel horizontal half wavelength radiators H5 and I5 for obtaining directivity in the vertical plane. Antennas l4 and H! are energized cophasally by high frequency apparatus which is coupled to the radiators through feeder lines which are connected at spaced points on the antennas matching the impedance of the feeders.

Figs. 9 and 10 illustrate directive antennas for use both at the transmitter and receiver for communication with vertically polarized waves, Fig. 9 obtains added horizontal directivity while Fig. 10 obtains added vertical directivity with respect to a single antenna.

The system of the invention, it has been found, produces a decided improvement at the receiver in being free from interfering signals arriving from sources of noise, such as ignition, which may be away from the direction of the transmitter. The reflector 3 at the receiver also eliminates reception of undesired signals from the rear of the receiver. There is produced a stronger signal at the receiver input due to power gain at both transmitting and receiving directive antennas.

From what has been set forth above, it will be understood, of course, that the invention is not limited to the precise details illustrated and described since various modifications may be made with-out departing from the spirit and scope of the invention. For example, in some instances, it may be possible to mount the antenna elements very close to the wall of a building and thus dispense with reflectors.

What is claimed is:

An ultra short wave signaling system comprising a transmitter and receiver mounted on buildings within the line of sight of each other and located in an area having objects which reflect the rays emanating from said transmitter, a pair of parallel horizontal directive antennas mounted one above the other at said receiver and spaced from each each other vertically a distance equal to sin {b where A is substantially the length of the mean operating wave, and b is the angle between the direct wave and the main reflected wave, each of said antennas comprising a pair of arms extending in the same straight line, a U-shaped loop of high impedance connecting together the adjacent ends of the arms of each antenna, means for cophasally combining energy collected by said pair of antennas, said means comprising a two-wire feeder coupled to points on said loops which match the impedance of said feeder, and a horizontal directive antenna at said transmitter.

2. An ultra short wave signaling system comprising a transmitter and receiver mounted on buildings within the line of sight of each other and located in an area having objects which reflect the rays emanating from said transmitter, a pair of parallel horizontal directive antennas mounted one above the other at said receiver and spaced from each other vertically a distance equal to sin ):b where x is substantially the length of the mean operating wave, and b is the angle between the direct wave and the main reflected wave, each of said antennas comprising a pair of arms extending in the same straight line, means for cophasally combining energy collected by said pair of antennas, said means comprising a twoconductor feeder coupled to said pair of antennas, and a horizontal directive antenna at said transmitter.

HAROLD H. BEVERAGE. PHILIP S. CARTER. GILBERT S. WICKIZER,