US1669219A - Method of reducing fading effects in radiocommunication - Google Patents

Description

May 8, 1928. 1,669,219

A. H. TAYLOR I METHOD OF REDUCING FADING EFFECTS IN RADIO COMMUNICATION Filed Feb. 17. 1927 IMIMI] INVENTOR. QEQI /Y d6 3 0 0,

ATTORNEYS.

Patented May 8, 1928 UNITED STATES PATENT OFFICE.

ALBERT H. TAYLOR, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO WIRED RADIO, INC., 01 NEW YORK, N. Y., A CORPORATION OF DELAWARE.

METHOD OF REDUCING FADING EFFECTS IN RADIOCOMMUNICATION.

Application filed February 17, 1927. Serial No. 169,045.

My invention relates broadly to signal transmission systems and more particularly to a system of transmission and reception wherein the undesirable effects of fading at receiving stations is substantially eliminated.

One of the objects of my invention is to provide a coordinated system of high frequency transmission and reception by radio where reliability in communication is assured independent of the effects of fading.

Another object of my invention is to provide a system of reception for high fre- 'quency transmission wherein continuous wave energy may be simultaneously received on identical radio frequencies but detected at different audible frequencies and the signaling energy integrated at a receiver responsive to all of the difierent audio frequencies for insuring reliable reception regardless of the fading of the signal energy from one audible frequency to another.

My invention will be more fully understood from the specification hereinafter following by reference to the accompanying drawing which shows diagrammatically one form of the receiving circuit which may be employed in carrying out the principles of my invention.

The most serious obstacle in obtaining results in radio communication using high frequencies, is the presence of fading which investigation has shown is due to varying in- I terference patterns at the receiving antenna due to varying combination of incident waves coming from several directions at once. It is plainly seen that at remote receiving stations the wave energy arrives by a number of different routes having suffered reflection from various portions of the Kennelly Heaviside layer (see Taylor & Hulburt paper in Physical Review for February, 1926) thus sending to the receiving antenna several electromotive" impulses which vary in amplitude and phase, as the reflecting and absorbing medium shifts about from moment to moment. These fading effects may be divided roughly into two 0 asses; one, a rather rapid fading efi'ect, fast enough to be within the audible range and which averages outin telegraphy, although it may be very disastrous to telephony, and a slower fading effect of a number of seconds of duration.

I have found that if two antennae, separated by at least a considerable fraction of a wave length are used with the receivers, that the signals do not fade in and out exactly at the same time on these two receivers. However, the problem of fading is very much more difficult of solution with continuous wave transmission than with modulated continuous wave operation.

An installation is representedin the draw ings having two antennae A and A and two single circuit regenerative receivers R and R which feed their outputs into the two primary windings 1 and 2 of the audio frequency differential transformer 3, the secondary winding 4 of which is connected to a receiving telephone 5. H and H represent two separate heterodynes or drivers which may be used in the place of autodyne reception, if desired. Consider first, the case of modulated continuous wave reception; the heterodynes will not be used and the regenerative receivers R and R will not oscillate.

In this case the variations in intensity of modulated signals on the two antennas A and A not being simultaneous, the telephones 5 will receive a sort of average result which will show a good deal less fading than reception from one antenna alone. Variations in the phase of the various components of the electromotive force received on the antenna at high frequencies will not influence the phase of the resultantaudio frequency which is determined in the receiver. Therefore, the arrangement will be of benefit in vave reception then the phenomenze are entirely different. Assuming that each re ceiver R, and R is tuned to the incoming signal and that they either oscillate at synchrony, or if theyI do not oscillate, then the two heterodynes 1 and H must oscillate in. synchrony, or as a still further alternative, the one receiver or else the one heterodyne will supply the local oscillations for both. The local osnillations will differ. by audible frequency from the incoming high frequency signal. In this case, however, whenever the phase of the resultant electromotive force on antenna A shifts, as it usually shifts when fading, (if fading is an interference phenomena), then the shift of the audio frequency produced by the receiver R al. o shifts and by the same amount in degree If the production of the beats between two high frequencies differing by the audible frequency is considered, it is readily observed that shifting the phase of either of the high frequencies, will shift the phase of the resultant beat note which is obtained after rectification by the detector, and will shift it by the same amount as the high frequency shift. The-same thing will happen in the antenna A at the output of receiver R,. The two audio frequencies, therefore in two primary windings 1 and 2 of the di erential transformer 3, are continuously shifting in phase with reference to each other as fading goes on differently in the two antwo receivers R, and

tennee A, and A Therefore, the fading on the whole, will not be reduced because there will be moments when these phases will be in opposition to each other and the intensities will be approximately equal which will result in the fading of signals. Under these conditions two antennae do notfunction any better than one antenna, and a very large number of antennae do not improve results except in so far as the system becomes directive by a suitable combination of antennae. It is possible, however, under many conditions to get a marked improvement in reception, using the arrangement shown in irrangements-can be made avoiding this difficulty of shifting hases by setting the 2 on slightly different audio frequencies, or if separate heterodynes are used, by oscillating them on different frequencies. The receivers actually receive the same fre uency but the circuits are offset so that the cat tones are different. For instance, suppose the receiving frequency is 4000 kilocycles, and one heterodyne is set at 3999 kilocycles, and the other one is set at 4001.2 kilocycles. The two primary windings .1 and 2 differential transformer 3 will then receive, due to the rectification in R, a beat frequency of 1200 cycles and due to the rectification in R a beat frequency of 1000 cycles. These two frequencies can not combine vectorially for neutralization. They will in general, give a double tone in the receiver 5 and as fading goes on, one tone or the other will predominate but the average readibility will be greatly improved. It may be objected at once that the two heterodynes, or autodynes, if heterodynes are not used, will give a difference frequency of 2200 cycles which 'would be very would drown out all signals. y way of example, suppose the receiving frequency is 8000 kilocycles. One receiver is set on 8001 kilocycles and the other on 8001.3 giving a beat note of 1000 cycles and 1300 cycles re-- spectively, on the same incoming signaling frequency. This is avoided by providing a tone filter or audio frequency trap 6 in .the circuit to the telephones 5 so as to trap out this undesirable frequency which is considerowerful and vention are intended other than are imposed by the scope of the appended claims.

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

1. A receiving system for high frequency signals comprising a plurality of radio frequency energy collecting circuits, separate receiving circuits coupled with said radio frequency energy collecting circuits, said radio frequency collecting circuits being separated by at least a considerable fraction of the wave length of the transmittedsignals, independent high frequency oscillators connected with each of said receiving circuits, said oscillators being arranged to operate at slightly separated frequencies, a common output circuit for said receiving circuits and a responsive device coupled to said common output circuit whereby signaling energy over a band of audio frequencies provided by said radio frequency energy collecting circuits actuate said responsive device.

2. In a system for reducing the effects of fading in high frequency signal transmission systems a receiving apparatus including in- I dependent radio frequency energy collecting circuits, each of said circuits being separate at least a considerable fraction of the wave length of the transmitted signals, independent receiving circuits connected to said separate radio'frequencyenergy collecting circuits, a responsive device, a circuit common to each of said receiving circuits, connections between said common circuit and said responsive device and separate high frequency generators coupled with said receiving circuits and each operative at slightly separated frequencies for combining the effects of signaling energy over a band of audio frequencies in said common circuit for controlling said responsive device.

3. A receiving system for reducing the effects of fading comprisinga plurality of antenna systems separated one from the other for at least a considerable fraction of the wave length of the transmitted signals, a.

receiving circuit connected with each of said antenna systems, separate generators of high frequency current/coupled to each of said 4. In a system for reducing the efiects of fading in radio reception the combination of a pair of separate antenna systems separated one from the other for at least a considerable fraction of the wave length of the transmitted signals, independent receivers connected with said antenna systems, separate generators of high frequency energy coupled with each of said receivers, adifferential transformer system having a air of primary windings and a single secon my windin' connections between the outputcircuits of said receivers and the rimary windings of said differential trans ormer system, a responsive device, and connections between said secondary device whereby the combined effects of said generators and signaling energy incident upon said separate antenna systems actuate said responsive device.

ALBERT H. TAYLOR.

winding and said responsive

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