US2067432A - Radio communication - Google Patents

Description

Jan. 12, 1937. H. H. BEVERAGE 2,067,432

' RADIO COMMUNICATION l Filed Dec. 5, 1923 2 Sheets-Sheet 1 Jan. 12, 1937. H. H. BEVERAGE RADIO COMMUNICATION Filed Dec. 5, 1923 2 Shees-Sheel 2 .MJNV

Patented Jan. 12, 1937 UNITED STATS PATENT OFFICE RADIO COMMUNICATION of Delaware Application December 5, 19.28, Serial No. 323,809

1 Claim.

This invention relates to radio communica-tion, and more particularly to a method and means for reducing the effect of fading when communicating on short waves.

To overcome the effect of fading when communicating on short Waves is the primary object of my invention, and to this end I propose a frequency diversity method, which includes the transmission and reception of the same signal on several short wave carriers having only slightly different frequencies. It is not feasible to employ widely different frequencies because the diurnal transmission characteristics then will differ, and during much of the day if one of the frequencies comes through the others will not, so that instead of having a diversity system there will be only one channel in operation. Furthermore it is far preferable to utilize slightly different high frequencies in accordance with my invention because less space in the available frequency spectrum is needed for each channel. I propose, for example,

to use a difference of the order of magnitude of that between 16 and 161/2 meters as a maximum, and, in the case of code signals, I nd that it is satisfactory to use a difference as slight as an audible frequency, say 2 or 3 thousand cycles per second. In this manner the general transmission characteristics are kept alike, but the instantaneous fading characteristics may differ widely.

I find that not only does the fading at any instant of two waves of slightly different high frequency continually Vary, but, consistently therewith, their relative phase also continually varies relative to the normal variation due to frequency difference. It therefore would be impossible to combine the radio frequency energies directly together, even if they were of the same frequency.

It therefore also is impossible to combine equal intermediate .frequencies together, after beating each of the received frequencies with a different local oscillator frequency such that the intermediate frequencies are equal, because the relative phase of the intermediate frequency energies fluctuate just like that of the incoming radio frequency energies, for if of two beating waves one is kept constant in phase, while the other is varied in phase, their beat is equally varied in phase. Now in accordance with my invention I overcome these difficulties by first rectifying the received energies, 0 and combining them only after rectification, so that the combination is substantially independent of radio frequency phase.

In the case of code communication I may employ two transmitters of different frequency, and key them simultaneously. In such case both transmitters transmit during marking periods, and not during spacing periods. As an alternative the transmitters may be keyed so that one is transmitting during marking periods, and not during spacing periods, While the other transmits during spacing periods, and not during marking periods. This possesses the advantage of making it possible to employ a single transmitter and to slightly detune the transmitter with the keying means, in order to obtain a back wave for the spacing periods.

At the receiver the radiated energies are collected, amplified separately or together, but, separately rectified, and then the marking energy is utilized to actuate a translating device in one sense, and the spacing energy is used to actuate the same translating device in the opposite sense, so that both and also either of the marking and spacing energies alone will produce a readable signal. To accomplish this effect in a very simple manner I reverse the phase of one of the rectified energies, preferably by putting the energy through a three electrode tube, and then combine the rectified energies in additive phase and apply the combined energy to a single translating dev1ce.

My invention is described more particularly in the following specification, Which is accompanied by drawings in which Figure 1 is a code communication system arranged for simultaneous transmission of the marking periods; Figure 2 is a modification applicable to signal modulation by speech or other speech-simulating signals; Figure 3 is an arrangement for alternate transmission of marking and spacing waves; Figure 4 is a section of tape explanatory of the operation of the arrangement shown in Fig. 3 Figure 5 is a system employing a single transmitter arranged for keying with a back wave, and a preferred form of receiver; and Figure 6 is a portion of recording tape explanatory of the operation of the receiver shown in Figure 5.

Referring to Figure l there are a pair of transmitters 2 and 4, each tuned to slightly different high frequencies, and each coupled to an antenna 6 and 8. Both transmitters are simultaneously keyed by a single keying means. which arrangement is schematically indicated by the key I0. connected in parallel to both of the transmitters. The details of the keying connections are immaterial, and may be of any conventional type, such as those which establish a high negative or blocking bias on the control electrode of one of the tubes in the transmitter.

The receiver cooperating with the transmitter shown in Figure 1 may be of simple form, comprising the antennas I2 and I4, and the amplifiers I6 and I8, each tuned to the frequency of one of the radiated waves. It should be understood that the amplifiers IB and I8 may include autodyne or heterodyne stages, so that part or al1 of the amplification may be performed at an intermediate instead of atthe original radio frequency. The amplified energies are fed to separate detectors 20 and 22, here illustrated as full wave rectiflers, the .output from which may be amplified in amplifier tubes 24 and 26, and then combined in a common relay 28, which, in the case of a remotely located translating'device 30, may be used to-key a tone generator 32 in order to transmit a tone signal on the land line 34 in accordance with the received code signal.

If it is desired to transmit speech, or other Speech-simulating signals, such as modulation for multiplex code or picture work, a very similar arrangement maybe employed, indicated in Figure 2, in which the transmitters'Z and 4 are modulated, rather than keyed, in any conventional manner, by a microphone or other source of modulating energy 36. The radiated energy is collected on antennas I2 and I4, amplified in amplifiers I6 and I8, rectified in rectiiiers 20 and 22,` to obtain the modulation energy, which then may be amplified in amplifier tubes 24 and 26, the outputs from which are combined in a single impedance 38, coupled to an amplifying tube 48, the anode circuit energy of which is fed, through a transformer 42, to any suitable translating device, here exemplified byv a loud speaker 54. 'Ihe two carriers used in this scheme should differ sufficiently 4it preferable to so key the transmitters that one transmits during the marking periods, while the other transmitsduring thespacing periods, and "such arrangement' has been'illustrated in Figure 3. Referring to this figure it Will be seen that the transmitters 52, and 54, instead of being coupled to separate antennas, as in Figure l, are coupled to a single antenna 56, but in this case the keying means 68 is arranged, as shown, to aifect the transmitters alternately, rather than simultaneously. The receiver, instead of employing separate -,a .nt ennasalso .hasa single antenna 62, coupled 'to amplifiers 66 and 68, which in turn lead to rectifiers 'IIJ and I2, the outputs from which may be amplified in amplifier tubes 'I4 and T6. However, the energies cannot then be directly combined t0- gether, as in Figure l, for they then act in the same direction and no useful effect on the recorder would be obtained inasmuch as they would add up to a constant value, and yield no signal at all. To obtain a signal these energies must be combined differentially, and this has been indiycated by the zero center differential relay 8U, ywhich, is presumed to control a spring centered contacting arm which closes the circuit (if the common line 8| with either the positively charged Y line 82, or the negatively charged line 84, accord- ',ing to whichoi the receivers .is being energized 'by the transmitter at that instant. The lines 82 a mean Zero line, both and also either of the marking and spacing energies will produce a readable This may be explained in connection with Figure 4, indicating fragmentary portions of a recording tape obtained from the translator 86 in Figure 3. Referring to Figure 4 it will be seen that relative to a mean zero line, when one of the signalling energies, say the spacing energy, fades, and the marking energy does not, a tape will be obtained showing the desired signal above the zero line, as is indicated at 98. I f, on the other hand, the marking energy should fade, while the spacing energy does not, a signal will be obtained below the Zero line, but readable with respect to its own lower base line, as is indicated at 92. However, should neither fade, a signal of amplified strength will be obtained, ranging between the extremes of the negative flow produced by the spacing Wave, and the positive flow produced by the marking wave, as is indicated at 94. Except in the event of simultaneous fading of bothY the marking and spacing energies, a readable signal will always be produced.

In Figure 3"the transmission system utilizes separate transmitters, but one is worked While the other is not. Only one being worked at a time suggests the possibility ofusing a single transmitter keyedwith aback Wave, and such an arrangement isA shown in Figure.5. Referring to that figure there is a tube |00, the anode to cathode and control electrode to cathode circuits of which are regeneratively coupled by the coils |82 and |84, which are tuned'by a tuning condenser |86. Direct anode and control electrode bias potentials are applied througlf'the leads |88 and I II) to either side of the blocking condensers VI I2 and I I4; The output of this oscillator may be amplified in any suitable power amplifier I I6, and radiated over an antenna system ||8. The oscillator is so keyed as to change its transmission frequency slightly. Two simple ways to do this have been indicated, in one of Ywhich a key.|28 is used to short circuit a portion of the 'inductance' of the resonant circuit, and in the' other of which a key |22 is used to vary the spacing of a small condenser I24, which is connected in parallel 'with the main tuning condenser |86. By thesek or any i other suitable frequency varying schemes a single transmitter may be employed in place of the two transmitters indicatedin Figure3.

The receiver shown in Figure 5 comprises an antenna |38, the energy collected by which isamplified in a radio frequency amplifier |32, and then heterodyned with energy from a local oscillator |34, in a'heterodyne detector |36, to' obtain intermediate frequency energy. This is readily separated into marking and spacing energies, by

the high pass filter |38 and the lowpass filter |48. The ltered energies are also respectively amplied in intermediate frequency amplifiers |42 and |44. The amplieroutputs.arerectified in suitabie remmers uis-ana las, this rectified currents from which are passed throughlow pass filter sections |50 and |52, which serve to by-pass the radio frequency components of the rectiedenergy, and to steady the rectified signal energies.

One ofthe rectified energies is reversed in phasep preferably bypassingitthrough a three electrode -tube |54, coupled by a suitablefcoupling Vresistance |56, and the anode circuit of the tube |54 is connectedto the anode circuit of the rectifier |48, as shown. The anode of vthe tube |54 is polarized by a suitable source of direct anode potential |58. The control electrode of the tube I 54 is biased from a bias batteryl', in cooperation with a potentiometer resistance |62, and the magnitude of the bias potential is so adjusted that itfwillbew75 overcome or made sufficiently negative by incoming signal energy to stop anode current from flowing. With this adjustment the pen of the translating device |64 normally will remain at a value above the zero axis, assuming no keying, because of the steady anode current from the source |58. Should one of the signals, say the marking signal, alone reach the receiver, and it be amplified and rectied in the units |44 and |48, the resulting rectified current will add to the steady anode current from the source |58, and a readable signal will be obtained above the normal base. This has been indicated at |10 in Figure 6, in which the dotted line shows the normal position of the pen. Should the marking signal fade, and the spacing signal alone reach the receiver, it will serve to negatively bias the tube |54, and so decrease its anode current to zero, resulting in a readable signal such as has been indicated at |12 in Figure 6. If both signals are received without fading, a signal of double amplitude is obtained, as is indicated at |14 in Figure 6.

It should be understood that either of the transmitters indicated in Figures 3 and 5 may be used with either of the receivers shown in Figures 3 and 5. It should also be understood that in any of the receivers the ampliers which precede the rectiers may include separate or combined heterodyne means followed by intermediate frequency ampliers. In code work the intermediate frequency may be as 10W as an audio frequency. Also, any of the rectiers may be equipped with 10W pass filters, such as has been indicated in Figure 5. The single antenna shown in Figure 3 may be used in connection with the other arrangements illustrated in Figures 1 and 2, instead of separate antennas, owing to the closeness of the two carrier frequencies. Full wave rectiers are not essential. More than two frequencies may be employed, if desired, particularly in the arrangements shown in Figures 1 and 2.

I claim:

An arrangement for reducing fading when transmitting code signals on short Waves including a transmission system comprising a short wave transmitter, keying means for slightly changing the frequency of transmission to distinguish between marking and spacing periods, and means to radiate the marking and spacing energies alternately, and a receiving system comprising means to collect the radiated energies, separate electron emission tube amplifiers for the marking and spacing energies, separate rectiers coupled to each of said ampliers, a three electrode tube coupled to the output circuit of one of the rectiiers for reversing the phase of the rectified energy, means coupling the anode circuit of the three electrode tube With the output circuit of the other rectifier so as to combine the marking and spacing energies in additive phase, and a translating device responsive to the combined energy.

HAROLD H. BEVERAGE.

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