US2069813A - Fading elimination - Google Patents

Description

Feb. 9, 1937.

H, H. BEVERAGE ET AL. 2,069,813

FADING ELIMINATION Original Filed March 15, 1928 .Fl I 1 I 6' 73 REgE/VL-R AMPL war I & 77 9 RECE/VE'R AMPZ/F/ER Fl g v 2 I 43 /5 l/VTERl/[fiMTf RECE/VER FRZ-"Ol/Z-WCY AMPZ/F/ER w 49 if Rico/205k ATTORNEY Patented Feb. 9, 1937 UNITED STATES PATENT orrle f FADING ELIIWINATION Original application March 15, 1928, Serial No. 261,738. Divided and this application February 10, 1936, Serial No. 63,132

12 Claims.

The invention relates to the elimination of what is commonly known as fading in wireless or radio signalling. It is particularly adapted for use in the reception and transmission of short wave signals, especially in locations where fading conditions are particularly troublesome.

This application is a division of our copending application, Serial No. 261,738, which was filed on March 15, 1928.

We have found that signals picked up on antennae located at different points have different fading characteristics, and that where short wave antennae are located at separated points that the signals might be of a maximum intensity at any particular instant on an antenna located at one point and at the same instant be of a minimum intensity on an antenna located at another point. In order to combine the signals received on the various antennae which are, as above stated, geographically separated with respect to each other, the first thought was to carry the radio frequency energy pickedup on the various antenna systems in question to some common receiver and to add the separate energies directly together at the common combining point. This, however, has its limitations because it has been found that the phase relationship between the signal voltage received at one antenna and the signal voltage received upon another antenna geographically separated from the first antenna does not remain fixed but changes from moment to moment. Therefore, it is relatively ineffectual to provide an arrangement for directly combining the radio frequency voltage from the plurality of antenna systems located at various geographically separated points since these voltages might add at one instant and subtract at another instant, due to the fact that the radio frequency voltages from the various antennae will not always be in phase. 7

. t is, therefore, an object of our invention to provide a method and means of combining signals from various geographically separated antennae independent of the phase relationship of the signals as received on the various antennae.

The broad idea of combining signals from various geographically separated antennae has been disclosed in our U. S. Patent 1,819,589, issued August 18, 1931.

Referring to the accompanying drawing, Fig. 1 illustrates an arrangement for combining signals in a receiving circuit independently of their relative phase; and

Fig. 2 illustrates a modification of Fig. 1.

.In Fig. 1 we have shown a method for liminating short wave fading in which the audio frequency outputs of two geographically separated radio receiving systems are addedwRadiofrequency energy of the desired signal is picked up on two geographically separated antenna systems, I and 3, which carry their respective energies to receiving systems of any desired character and 1. Associated with the receiving systems 5 and 1 are two separate local oscillators 9 and II, there being one oscillator for each receiver system. These oscillators are used to heterodyne the incoming signal energy as received upon the geographically spaced antennae l and 3. In each receiving system 5 and I, which are intended to include the usual detector circuits, the outputs of the detectors arefed through-any desired form of leads to amplifiers l3 and I5. The outputs of amplifiers l3 and 15 are impressed upon the primary windings l9 and 2| of the transformer I! from which the energy is transferred to the secondary winding 23. Included in the'secondary circuit 23 are a set of phones or any other type of receiving unit or translating device 25.

It will be noted from the above that there is one primary winding H9 or 2| for each receiving system l or 3 and that the secondary winding 23 of the transformer ll contains two different frequencies from the two different receiving systems. The heterodyne oscillator 9 which is coupled with receiving system 5 is preferably so adjusted that the beat note resulting may be of the order of 800 cycles. The oscillator which is coupled with the receiving system I is preferably so adjusted that the beat note resulting may be of'a frequency of 1,000 cycles, although it is to be understood that we can successfully use beat frequencies other than those which we have mentioned. It is thus seen that there is an 800 cycle output from receiving system 5 and al, 000 cycle output from receiving system I. These two frequencies which will now be denoted by F1 and F2, respectively, are passed through the two primary windings l9 and 2| respectively of the output transformer l1 and both frequencies appear in the secondary winding 23 which is connected with the receiving instrumentality such as the phones 25.

If an operator is listening in the phone 25, he may note that in one instant the 800 cycle note I or frequency F1 at one time predominates, due to the factthat the energy picked up by the antenna system I which is connected to this receiver is greater than the energy picked up by the antennasystem 3 connected with receiving 'pr-eciable length of time.

system 1. However, at another instant it might appear to be that the 1,000 cycle note, or frequency F2 will predominate in the phone 25, due to the fact that the energy. picked up by the second antenna system 3 is now greater than that picked up by the-antenna system of the first receiver 5. q

It is thus seen that there are two different frequencies in the secondary of the transformer l1 oscillators 'as'has been above described, to produce twqdifferent audio frequency outputs, an arrangement can be established where the audio frequency outputs inan output transformer are arranged ,to, obtain satisfactory reception since one beat note will predominate at one instant and "another beatnote will predominate at another instant, but at all times whenany signals reach antenna or 3 the operator will have a signal inphones 25.

It is thus seen'that We have produced by this arrangement a methodand apparatus which will effectively eliminate the efiect of fading by combining the signals received on each of the two or more geographically separated antenna systems independently of the phase relationship.

From the above description it is obvious that the same method and principle may be used ,tocombinethe outputs of morethantwo antennae. Thus,'to combine the outputs from n antennae, in accordancefwith the principle above set forth, n receivers would be used and produce n different frequency outputs which would all add theirenergiestogether in the common receiving instrumentality, as for example; the phones 25.

As also will be understood from a reading of the above description it will be noted that the speed of signalling is practically a function of the frequencies transferred to the receiving instrumentality. Therefore, if it is necessary to increase'the speed of signalling to any great extent itis advisable to substitute two low radio frequencies for the frequencies referred to above as F1 and F2. I g V In order to adapt the system shownby Fig. 1

'to higher signalling speeds, it isdesirable to modify the showing of Fig. 1 to operate with low radiofrequencies for F1 and F2. Fig. 2 shows a suitable form for such a'modification. Referring now to Fig. 2antennae 3| and 33 are coupled to transmission'lines 39 and 4| by suitable means, such as transformers 35' and. 31.

45* respectively. Each of the receivers-43 and 45 heterodyne the received signal to a lower frequency, either'by autodyne reception, or by using separate oscillators 4| and 49. For exampla oscillator 49 maybe adjusted to produce a'beat frequency F1 of 40,000 cycles, and oscillator49fmay'be adjusted to produce a beat frequency F2 of 42,000 cycles on the same signal. The outputsof receivers 43 and 45 are con.- nected in ai'suita'ble'manner to an intermediate frequency amplifier 5|; which amplifies F1. and

V The transmission lines 39'and 4| terminate at receivers 43 and F2 equally, but is selective enough to exclude undesirable frequencies lying outside of the 40,000 to- 42,000 cycle band.

Amplifier 5| is connected to the primary 53 of transformer 55. The secondary 51 of this transformer 55 is associated with a full wave rectifier consisting of devices 59 and 6|. The rectified current output of the rectifiers 59 and BI is ar- ..ranged to operate a recorder or other suitable receiving instrumentality 65. Connected across the output of the rectifier for the purpose of suppressing the beat frequency between F1 and F2, while allowing the relatively low frequency keying impulses to pass is a capacity element 63. In the example cited, where F1 has been chosen, for example, as 40,000-cycles and F2 as 42,000 cycles,

the beat note will'be (F2F1) or 2000 cycles, and I with a full'wave rectifier, this would largely appear as the second harmonic, or 4000 cycles. The

keying pulses have a fundamental frequency of about 40 cyclesper second fora Morse-code speed of 100 words ;per minute. [Hence it will be seen that the capacity 63 will have 100 times ,more

shunting effect on the combination frequency than on the keying frequency in the example cited. If greater speeds'of transmission are desirable,-condenser 63 could be replaced by a'low pass filter, which would pass high speed keying impulses, but would entirely suppress the combination frequencies.

While Fig. 2 and the description pertaining thereto has been illustrated by showing two antennae and assuming a frequency difference of 2000 cycles, it is to be understood that several antennae could be combined by utilizing-more receivers and combining the outputs of these receivers in a suitable intermediate frequency amplifierwith suitable spacing between'the different heterodyne frequencies.

The principles involved in Fig. 2 are fundamentally the same as in Fig. 1, excepting that a receiving instrumentality has been substituted which willbe operative over a wider band. of frequencies. than the phones of 1. frequenciesFi, F2; F3, etc. arediiferent, the phase relations between them change at avery-high rate as compared withboth the rate of fading and the rate of keying. Therefore, it is possible to suppress the combination frequencies without interfering with the keying pulses, ashas already been explained. Hence, it is seen that changes Sincethe in radio frequency signal phase between the several'antennae, have no effect on the final rectified output, and'that the energies are added in the recorder irrespective of phase relations.

This results in a final signal output-relatively free from fading at the receiving instrumentality,

provided that-the several antennae have been located for suitable fading diversity. 'We have found that a spacing on the order of 1000 feet between antennae gives excellent diversity on short Wave signal fading, for example, onwave lengths up to at least 30 meters.

We claim:

'1. The method of receiving wireless signals with geographically spaced antenna systems which comprises receiving, the same signal upon each of a-pair of geographically lseparated'antenna systems and producing a pair of signal effects therefrom, producing in each of said receiving systems associated with said geographically spaced antenna systems a beat note of different.

frequency, combining and then rectifying the separate beat notes fromeach of said antenna:sys-' temsin a receiving circuit whereby the separate signal energies are combined independently of their relative phase relationship and the effects of fading are substantially eliminated.

2. The method of receiving wireless signals with geographically spaced aerials which comprises, receiving the same signal upon each of a pair of geographically separated aerialsand associated receiving systems for producing a pair of signal effects therein, introducing s'eparate'frequency energy in each of said receiving systems for producing a beat note of dififerent characteristics in each of said receiving systems, combining and then rectifying the said beat notes produced in a combining circuit whereby the signals received upon each of said geographically separated receiving systems may be combined independently of the phase relationship of the signals reaching the same and the effects of fading substantially reduced. I

3. The method of receiving wireless signals With geographically separated aerials which comprises, receiving the same signal upon each of a plurality of geographically separated aerials, and producing a plurality of signal effects thereon directing the energy from each of said aerials to separate receiving systems, introducing into each of said receiving systems a second frequency and producing a beat frequency differing in character in each of said receivers, amplifying the beat frequency produced in each of said systems, combining and then rectifying the separate beat frequencies in a combining circuit whereby the effects of fading are substantially eliminated and the signals received upon each of said aerials are combined independently of the phase relationship.

4. An apparatus for the elimination of fading comprising, a pair of geographically spaced antennae each adapted to receive the same signal effect, a receiving system associated with each said antenna, means for producing beat notes in each of said receiving systems, said beat notes differing in frequency in each of said systems, a combining circuit, a responsive device, and means for so combining and rectifying the beat notes from each of said systems that the received signals as sensed by said responsive device are substantially unaffected by fading and are combined independently of the phase relationship of the signals reaching said antenna.

5. An apparatus for the elimination of fading comprising, a plurality of geographically spaced antenna systems for receiving the same signal effect, a receiving system associated with each of said antennae, an oscillator of different frequency associated with each of said receiving systems, means for producing a beat note by the action of said oscillator frequency upon said received signal frequency, means associated with each of said receiving systems for combining and then amplifying the beat notes so produced, a beat frequency detector responsive to the combined energy from said amplifying means and means associated with said beat frequency detector and so characterized that upon operation in response to signals simultaneously received by said plurality of antennae the effects of fading are substantially reduced independently of the phase relationship of the signals reaching said antenna systems.

6. An apparatus for the elimination of fading comprising, a plurality of antennae each having different instantaneous fading characteristics, a separate receiver associated with each of said antennae, means for producing difierent output frequencies from said receivers for the same received'signals a common selective intermediate frequency amplifier, a rectifier coupled with the output of said intermediate frequency amplifier, a receiving instrumentality associated Withthe output circuit of said rectifier and a condenser shunting said output circuit, whereby signals received upon said antennae are received in said receiving instrumentality'substantially unaffected by fading and are combined independently 'of the phase relationship of the signal reaching said antennae. a A

7 An apparatus for the elimination of fading comprising, a plurality of geographically spaced antennae each having different instantaneous fading characteristics and each adapted to receive the same signal energy, a separate receiver associated with each of said antennae, means for producing a different radio frequency heterodyne beat note on the same signal with each receiver, a selective intermediate frequency amplifier associated with the output of each of said receivers for equally amplifying the separate beat frequencies, a full wave rectifier connected with the output of said amplifier, a filtering means connected in the output circuit of said rectifier, and a receiving instrumentality also associated with said rectifier in the output cire relatively high frequency at separated places,

combining said waves received at said places with combining waves of frequency different from that of the received waves to produce intermediate frequency waves of frequency lower than that of said received Waves, the frequency of said combining waves being different at different ones of said places, whereby intermediate frequency waves of different frequency result from said combining actions, adding said Waves of intermediate frequency to produce a resultant wave, and detaching the signal component of the' latter wave as a relatively low frequency signal current.

9. The method of reducing fading effects in the reception of radio signals, which comprises receiving at a plurality of receiving stations radio signals transmitted from the same transmitting station, beating the received signals at each receiving station to an intermediate frequency, the said intermediate frequency being different for different ones of the receiving stations, transmitting the said intermediate frequency currents from each receiving station to a common station and combining and then rectifying at the latter station the said intermediate frequency currents.

10. In a radio signaling system, the combination of a plurality of receiving stations, each having means to receive a signal sent by the same transmitting station and to beat the received signal to an intermediate frequency, said intermedi ate frequency being different for different ones of the receiving stations, means to combine and then rectify the intermediate frequency signals of all receiving stations and means responsive to the energy so combined andrectified.

11. In a radio signaling system, the combinetion of a plurality of receiving stations having means to receive signal waves of the same frequency, means for supplying combining-oscillations to all receiving stations, said combining oscillations being different for different ones of the receiving stations to'produce with the received signal waves at the receiving stations intermediate, frequency Waves of different frequencies, means to add the intermediate frequency waves from all of the stations to produce a resultant 'wave, and means to detect the signal component of the said resultant wave.

'12. A multiple station radio receiving system comprising a plurality of separated radio receiving stations, antenna means at each separated station for collecting from the ether a signal modulated wave of high frequency, means at each of said separated stations for producing,

from said signal-modulated wave of high frequency, signal-modulated waves of intermediate frequencyvwhichare different for each station,

' and a singledevice for detecting" the signal corn- 7 ponent of said waves.

HAROLD'H. BEVERAGE. HAROLD O. PE'I'ERSON.

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