US 2108878 A
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Description (OCR text may contain errors)
Feb.'22, 1938. G W T 2,108,878
RADIO RECEIVING SYSTEM Filed Aug. 25, 1935 Signal, 4 channel.
1 Band F s I mie 7 Garner chamneb -neccwm 6 flPPd-mtufi carrier -Am LQfLer aebector curcuw INVENTOR GEORGEM BICE WRIGHT BY a I ATTORNEY Patented Feb. 22, 1938 PATENT OFFICE RADIO RECEIVING SYSTEM George Maurice Wright, Chelmsford, England, assignor to Radio Corporation of America, a corporation of Delaware Application August 23, 1935, Serial No. 37,464 In Great Britain August 30, 1934 V 4 Claims.
This invention relates to radio receivers and more particularly toso-called homodyne receiv-- ers, i. e., to receivers wherein received modulated carrier energy is mixed with an unmodulated car- 5 rier of the same frequency as the carrier component in the received modulated energy to detect the signals. More specifically the invention relates to homodyne receivers of the kind wherein the unmodulated carrier for mixing with the received modulated energy is not a locally generated frequency but is obtained from the received energy itself by separating out therefrom energy of carrier component frequency and amplifying this separated out energy.
A typical known homodyne radio receiver of the kind above referred to comprises a receiving aerial which is connected to supply energy to two channels A, B, in parallel. The first channel A, which may for the sake of convenience be termed the signal channel, comprises a band pass filter adapted to pass the desired received modulated carrier frequency with one or both of its side bands (as may be desired), followed in cascade by an amplifier for amplifying 5 the received carrier and its side band or side bands, the amplifier being again followed in cascade by an isolator circuit whose output is fed to the receiving apparatus proper. The second channel B, hereinafter referred to as the carrier channel, comprises a selector circuit for selecting the carrier component from the received energy in the aerial, this selector circuit being followed in cascade by an amplifier for the selected carrier energy, the output from this amplifier being mixed in the input circuit of the receiving apparatus proper with the output from the isolator in the signal channel.
Now it will be appreciated that successful operation of a typical known homodyne receiver,
as just described, depends, inter alia, upon the obtaining of very complete screening as between the two channels A and B and in particular upon the obtaining of a very high degree of isolation in the isolator circuit, for any leakage of amplified carrier energy from the amplifier in the carrier channel B-either through the isolator circuit or due to imperfect screening between the channelsmay easily result in the whole system bursting into self-oscillation at a frequency de- 5 termined by the constants of the various circuits and not controlled by the carrier emitted by the distance transmitter desired to be received.
The object of the present invention is to provide an improved homodyne receiver of the kind 55 referred toi. e., of the kind wherein the carrier energy for mixing with the modulated energy is derived from the received energy-wherein the above mentioned difiiculties are avoided, and wherein satisfactory operation can be obtained without recourse to extremely careful 5 screening or extremely careful isolation.
According to this invention in its broadest aspect, a homodyne receiver of the kind referred to is characterized in that the carrier energy for mixing with the received modulated energy for 10 the homodyne action is derived from a separate receiving aerial which is as nearly as possible completely uncoupled from a second receiving aerial which is utilized to receive the modulated energy. The first mentioned aerial feeds its out- 15 put into a carrier channel and the second mentioned aerial feeds its output into a signal channel, the outputs at the far ends of the two channels being combined or mixed as in the usual way. With an arrangement in accordance with this invention, it is unnecessary to provide an isolator at the output end of the signal channel, though, of course, an isolator may be provided, if desired.
Preferably the two aerials are constituted by mutually perpendicular frame aerials and in use 25 the mutually perpendicular frame aerials are so oriented that the incoming direction of the signals to be received bisects the angle between the aerials.
In one way of carrying out this invention and 30 illustrated in the single figure of the accompanying drawing a homodyne receiver of the kind referred to comprises a rotatable aerial system I consisting of two mutually perpendicular frame aerials Ia lb arranged to be rotatable together 35 about an axis 0. The output from one frame aerial I a is passed to a signal channel A comprising a band pass filter 2 adapted to pass the received carrier and one or both side bands (as may be desired), this filter being followed by an 40 amplifier 3 for the received carrier and side band or side bands. The second frame aerial lbfeeds into a carrier channel B comprising a carrier selector circuit 5 for selecting the carrier component of the received energy, this selector cir- 5 cuit being followed by an amplifier 6 for the carrier energy. The outputs from the signal channel and the carrier channel are combined in the input circuit of a receiving apparatus proper l as in the usual way. In use the aerial system I is so oriented that the incoming signal direction (indicated in Figure 2 by an arrow) bisects the angle between the frames in and lb.
It will be appreciated that with a homodyne receiver in accordance with this invention, and
as above described, difficulties of screening and isolation are much reduced as compared to known homodyne receivers of the kind referred to, and in fact such difiiculties are almost completely eliminated for there is no coupling between the two channels via a common receiving aerial while the coupling between the two receiving aerials employed is made as nearly as possible equal to zero. V
Having now particularly described and ascertained the. nature of my said invention and in what manner the same is to be performed, what I claim is: 7
1. A modulated carrier wave homodyne receiver of the kind referred to, comp-rising a pair of separate receiving aerials which are substantially completely uncoupled from one another, means coupled to one of said aerials for deriving only the 7 carrier energy for mixing with the received modulated energy for the homodyne action, and means coupled to the other of said aerials for deriving the modulated energy with which the carrier energy is to be mixed. 1
. 2. A receiver according to the invention defined in the preceding claim, wherein the pair of receiving aerials are constituted by two mutually perpendicular frame aerials.
3. The method of homodyne reception which consists in deriving a modulated carrier wave from one source, deriving a modulated carrier wave from a second source which is substantially completely-uncoupled from the first source, filtering and amplifying the modulated wave from the first source, selecting and amplifying only the carrier from the second source, and then combin- 1 stantially no coupling therebetween, a circuit connected between one of the signal, collectors and the receiving apparatus, said circuit including filter means and an amplifier, and a circuit connected between the other signal collector and the receiving apparatus, said second circuit including means for selecting only the carrier and means for amplifying said carrier.
GEORGE MAURICE WRIGHT.