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A simple and effective technique is presented to reduce the limit-cycle oscillation (LCO) in the reconfigurable rectifier for wireless power receiver. It is theoretically analysed that only one switching edge of the switching signal is needed to be synchronised and a phase-shift circuit is proposed for synchronisation. Simulation results in commercial 0.18 µm CMOS technology show that the LCO is greatly suppressed with the proposed synchronisation circuit and the output voltage ripples are much smaller compared to the conventional circuit.

To increase the bandwidth of a wideband receiver for surveillance applications, an in-phase/quadrature-phase (I/Q) channel-based receiver is a potential approach. However, the image caused by an imperfect coupler prevents the I/Q channel-based receiver from becoming a reality. Air Force Research Laboratory developed an imbalance compensation method covering two Nyquist zones. In this study, the authors present its implementation with a field-programmable gate array board. Experimental results demonstrate the effectiveness of the proposed imbalance compensation algorithm and its feasibility.

A Doppler radar based microphone is similar to an acoustic microphone except that it detects vibrations rather than sound. A microphone with a logarithmic square-law detector for monitoring honeybees is described. The performance of a logarithmic square-law detector is compared with a more conventional zero-intermediate frequency (IF), direct down conversion receiver. It is shown that unavoidable coupling between the transmitter and receiver as well as stationary clutter have the same effect in the square-law receiver as the local oscillator signal and mixer have in the direct down conversion receiver. The theoretical output of either configuration is formally the same. Both receiver designs were implemented in a low-cost, low-power radar microphone operating in the unlicensed 5.8 GHz industrial, scientific and medical band. The use of a logarithmic square-law detector resulted in a significant simplification of the radar microphone design as well as a 10 dB improvement in signal-to-noise ratio.

We report a fully integrated serial-link receiver with optical interface fabricated with a 0.18 µm complementary metal oxide semiconductor technology for long-haul display interconnects. The receiver includes a trans-impedance amplifier, a limiting amplifier, a clock and data recovery circuit, 1:64 de-multiplexer and a built-in error checker. The receiver produces 64-bit wide electrical signals from photodetector output signals produced by 5.28, 5.6 or 6.25 Gb/s optical signals delivered through up to 700-m multi-mode fibre. It can support serialised data for Ultra eXtended Graphics Array (UXGA), 1080 p and Wide Ultra eXtended Graphics Array (WUXGA). The receiver core occupies 0.59 mm2 with 42.4 mW power dissipation at 6.25 Gb/s bit rate from a 1.8 V supply.

A design technique to realise a low-complexity multiple-input multiple-output (MIMO) receiver using a time-multiplexed single front-end receiver is introduced. The architecture uses a simple front-end receiver where it delivers radio frequency signals to baseband section. The theory behind this architecture is analysed and the diversity gain of the proposed receiver is investigated. This simple MIMO receiver can provide the same diversity gain as the diversity gain of the multiple front-end. Moreover, the experimental studies are conducted to evaluate the diversity gain of the proposed architecture. Excellent agreement between the simulated and measurement results is obtained. The proposed architecture provides a new receiver design technique with lower complexity, power consumption and cost in MIMO systems.

This study compares the key parameters of two integrated receiver front-end architectures: low noise amplifier (LNA) with active mixer against LNA with passive mixer. The authors discuss the differences in the performance and their impact on system characteristics for radar applications. A low-IF down-conversion receiver implementation is considered. The results are compared in measurement for two 24 GHz receiver front-end chips realised in a 0.13 mum digital CMOS process. Both circuits have been characterised over automotive temperature range -40 to 125degC. The front-end with an active mixer offers lower LO power dependence and exhibits better temperature stability, whereas the front-end with a passive mixer has the advantage of better input-referred linearity and lower flicker noise.

A W-band dual-channel receiver is presented for the frequency-modulated continuous wave radars. In order to improve the isolation between two RF channels, a compact active power divider is implemented by a dual-output local oscillator (LO) amplifier. The temperature-compensated circuit also mitigates the gain variation of the receiver according to the ambient temperature. The fabricated receiver integrated circuit shows a conversion gain of 16 dB, a noise figure of 6.4 dB, and an input 1 dB compression point of -13.4 dBm at RF frequency of 76.5 GHz and LO input power of -1 dBm. The channel-to-channel isolation is >33 dB and the conversion gain variation is as low as -0.031 dB/°C between -40 and 120°C. This is the first temperature-compensated multi-channel receiver demonstration in W-band.

A fully integrated low-voltage RF receiver front end for 5 GHz radio applications, implemented in a standard 0.18 μm CMOS technology, is presented. The receiver consists of a differential low noise amplifier, an active mixer, and a quadrature voltage-controlled oscillator. The complete receiver is packaged in a standard 24-pin ceramic flat pack and consumes 56 mW from a 0.8 V supply. Measurement results show that the receiver has an overall noise figure of 7 dB, a −1 dBm input-referred IIP3, and 22 dB of image rejection. A stand-alone single-ended version of the LNA is also presented. Simple mechanisms for tuning the gain and the centre frequency of the LNA are proposed. With a supply voltage of 1 V, the LNA provides a power gain of 13.2 dB, has a noise figure of 2.5 dB, and over 10 dB of gain control and 360 MHz of frequency tuning. The LNA still operates well from a supply voltage as low as 0.7 V, providing a power gain of 7 dB.

The low-IF receiver architecture has already proved its effectiveness in mobile radio applications such as GSM. By using an IF of half the channel spacing to facilitate the removal of DC offsets, it achieves the sensitivity of a conventional superhet whilst offering the full integration potential of a direct-conversion receiver. Previous attempts to improve its multi-mode capability have focussed on digitising as much as possible of the IF signal chain with the help of a complex ADC. The channel filtering then moves into the digital domain where reprogramming is comparatively easy for operation in other modes. However, the combination of an increased dynamic range requirement and the need for a complex ADC can make the circuit design problem unduly difficult. In the receiver architecture to be described, the need for a complex ADC is avoided by processing only the real part of the low-IF signal. This substantially simplifies the ADC design whilst retaining all the advantages of a digitised, low-IF receiver. Simplification of the ADC design is the main objective but there is also scope for a 17% reduction in power consumption.

Broadcasting within the traditional AM bands is set to change with the introduction of digital broadcasts. Wideband receiver architectures allow many of the advanced functions of standards such as Digital Radio Mondiale to be implemented and upgraded without changing the hardware. This article describes some of the design issues of wideband receivers and the performance of a practical receiver.

A generic opto-electronic receiver structure, is analysed and conditions are specified which, when valid, result in a receiver with double the signal to noise ratio of a standard optoelectronic receiver. Experimental results from a high-gain, low-bandwidth, transimpedance amplifier are presented to verify the theory and to show that this performance level can be attained. It is shown that the bandwidth and overload sensitivity of the dual sensing optoelectronic receiver can be comparable with that of a standard receiver.

In this Letter, performance analysis of an impulse radio (IR) ultra wideband (UWB) correlation based receiver utilising non-coherent detection of orthogonal signalling is provided. The receiver's performance is presented through analysis and simulations in the additive white Gaussian noise (AWGN) channel. Results which show that in non-coherent detection of binary orthogonal signalling there is a difference between the traditional narrowband and IR approaches are provided. In the narrowband communication, there is a well-known, approximately 1 dB, difference between coherent and non-coherent orthogonal signal detection in AWGN. It is demonstrated here that in the binary orthogonal signalling of IR receiver the difference between coherent and non-coherent detection is insignificant, only tenths of decibels. This can be significant piece of information while considering different receiver structures for wireless sensor networks.

This Letter proposes a novel optical duobinary transmission system with no receiver sensitivity degradation. The transmitter yields a narrowband optical signal, and the receiver configuration is as simple as a binary IM-DD receiver. The feasibility of the proposed system is experimentally confirmed at 2.5, 5 and 10 Gbit/s.

A receiver for PSK optical signals is analysed. The demodulation is performed directly by launching the received signal into an injection-locked semiconductor laser. The locked laser conversts phase modulation into current modulation, which is sent to the data detection system after some signal processing. The signal to noise ratio of the receiver can reach 4599O 2 for a 100Mbit/s rate and a 100Khz emitter linewidth, where O is the phase deviation of the modulator

Two essential requirements of a non-communications electronic support system are a high probability of intercept and a high probability of detection against scanning microwave band emitters. High probability of intercept is typically achieved using a wideband receiver whereas high probability of detection requires a narrowband receiver. Achieving both has hitherto required the use of multiple receivers in a cascaded or channelised architecture. To minimise the cost for radar warning receivers and anti-radiation systems, the authors propose that a single scanning narrowband receiver with inherently high probability of detection can achieve a high probability of intercept by using an optimised search strategy to control its frequency scan pattern. In this study the authors have presented a new approach to assessing the performance of strategies based on probability of intercept and demonstrated the use of an evolutionary algorithm to optimise receiver search strategies. The optimised strategies show a significant performance improvement over traditional scheduling approaches.

Ultra-high-frequency radio frequency identification reader receiver is implemented in 0.18 µm CMOS. Based on the key parameter analysis for the reader receiver, the dynamic range concept is proposed to define the specifications and evaluate the performance of a reader receiver. The presented receiver utilises a quadrature direct-conversion architecture which consists of passive mixers, baseband programmable gain amplifiers (PGAs) and low-pass filters (LPFs). Both good input matching and as high as 10 dBm input P1 dB of the RF front-end is achieved by utilising the passive mixers driven by square wave local oscillators. In the analogue baseband, four PGAs provide a gain control range higher than 80 dB and the LPFs have a reconfigurable bandwidth from 100 kHz to 1.6 MHz to optimise noise performance under different Rx data rates. The on-chip DC-blocker with controllable cut-off frequency is proposed to avoid DC offset problems and obtain a fast settling time simultaneously. In the normal mode, the receiver sensitivity achieves −74 dBm with 12.9 dB output signal-to-noise ratio. An alternative radio frequency receiving path with a low noise amplifier (LNA) improves the receiver sensitivity in the listen-before-talk mode by 14 dB. The total power dissipation is only 58 mW with 1.8 V supply voltage.

Receiver timing synchronisation is a significant challenge for impulse radio ultra-wideband (IR-UWB) systems due to the low received power and narrow pulse width. In a coherent receiver, the local template pulses need to be synchronised with the received pulses with a precision of tens of picoseconds. Because of the periodic reduction in received correlated power, the traditional two-stage synchronisation method (acquisition and tracking) is not suitable for a single-path IR-UWB receiver. A tracking only, dual-loop delay-locked loop (DLL) with a 100 ps minimum phase shift is proposed to overcome this issue. This dual-loop DLL, employing a higher frequency fine loop, exhibits a better jitter transfer characteristic compared with a conventional dual-loop DLL. Measurement results of a 130 nm CMOS prototype indicate a locking frequency range of 30–120 MHz, and a best output jitter of 5.9 ps-rms (input reference jitter is 2.9 ps-rms). The total power consumption is 1.8 mW with a 1.2 V supply voltage.

A new receiver structure that alleviates the required sampling rate of analogue-to-digital converters for optical transmission is presented. The structure divides the received wideband signal into a number of narrowband signals with no guard band. A prototype of the band-divided receiver, which processes a 6 GHz-bandwidth received signal, is developed and experimentally evaluated in a real-time OFDM receiver. It is shown that a single-polarisation 12 Gbit/s OFDM signal can be demodulated using a 1.5 GS/s ADC.

A front-end optical receiver in 0.6 m BiCMOS technology is introduced to maintain equally spaced levels and constant output signal swing for multilevel signals at different input optical powers. The symbol error rate measurements for 4-PAM signals show a better sensitivity than with a conventional optical receiver. It is believed that this is the first time that complete performance characteristics for an optical receiver front-end designed especially for multilevel data transmission have been reported.

Windowing is often applied at the DMT (discrete multitone) receiver to suppress radio frequency interference (RFI). The spectral roll-off of the window determines how neighbouring tones are affected by RFI. However, the roll-off of the window is not of equal importance in all frequency range. In particular, the roll-off in high frequency will be inconsequential when the side lobes are so small that RFI is not the dominating noise. The window is designed here to minimise total interference. The frequency response of the proposed window achieves a good trade-off in spectral roll-off between high and low frequencies. As a result, fewer tones will be dominated by RFI than in the cases of commonly used Hanning and Blackman windows, in which the stopband in high frequency are often over designed. We have considered the case for informed receiver (RFI information available to the receiver) and uninformed receiver (RFI information unavailable to the receiver). In either case, the proposed window is channel-independent and can be obtained in a closed form.

A binary differential impulse radio-ultra wide band (IR-UWB) communication scheme over a single-mode optical fibre is examined. For a receiver structure, the conventional electrical receiver as well as an optical receiver structure, which is similar to the optical receiver used for digital, optically phase-modulated differential phase shift keying, are considered. The optical receiver can alleviate the IR-UWB receiver implementation challenges and it is studied for the first time in the context of IR-UWB. Considering various important noises, for example, phase noise, laser intensity noise, thermal noise and shot noise, analytical expressions for the error probability of the aforementioned receivers are derived. The mathematical models for optical components including laser diode and single-mode fibre, along with the analytical expressions for the receiver's error probability, are used to evaluate the overall performance of an UWB communication system over a fibre transmission medium. Furthermore, the electrical receiver is compared with the optical receiver and it is shown that the performance of the optical receiver can be as good as that of the electrical receiver and even better. The impact of wireless channel fading, bias current of laser diode and the coherence time of laser diode on the UWB over fibre system performance is also examined.

Ultra-wideband (UWB) is a very promising wireless technology for short ranges, because of its many benefits. A common practice in UWB is time hopping (TH)-PAM impulse radio system, in which a number of extremely short pulses are transmitted for each bit and the polarity of pulses determines the bit. In multi-user environments, the interference from other users [multiple access interference (MAI)] may well dominate the Gaussian noise which makes the matched filter receiver be a suboptimal receiver. A model for the statistical structure of MAI in an additive white Gaussian noise channel is presented. Then, using this model, the authors propose a nonlinear pulse combining scheme for the receiver of TH-PAM systems. The bit error rate (BER) of our receiver is compared with that of matched filter receiver and blinking receiver, via simulations. The simulation results show that our receiver always outperforms the matched filter receiver. Blinking receiver performs better than our receiver only when the probability of collision is low and the energy of interfering users is high. In all other cases, our receiver has a lower BER than the blinking receiver. Furthermore, the blinking receiver needs to know the locations of all the interfering pulses, while in our method such information is not required.

The effect of UWB interference on a Wi-Max receiver has not been addressed in the literature. This effect is analysed and it is shown that for a realistic scenario a DS-UWB system interference will not have a destructive effect on the performance of a Wi-Max receiver.

A simple and successful design for a sampling receiver that consumes very little power is presented. Measurements from a prototype receiver that show the potential of this technique are presented.

A simplified receiver implementation for optical differential 8-level phase-shift keying using direct detection is proposed. This implementation reduces the number of optical components in the receiver to half. The impact of non-ideal receiver parameters is analysed and quantified for a 1 dB OSNR penalty.

A multirate successive interference cancellation (MSIC) receiver for UMTS uplink is presented. The receiver takes into account the multirate nature of the UMTS signal based on variable length codes to select the strongest user, which is detected and cancelled. The proposed scheme outperforms other commonly employed receivers such as the minimum mean squared error receiver and the correlation receiver.

The paper presents analytical expressions for determining noise and intercept points for cascaded radio receiver stages. The theory allows for active receiver stages with frequency selectivity and flexible impedance levels. This makes the method highly usable for planning of modern receivers where baseband stages significantly influence the overall performance. A simple homodyne receiver example is used to demonstrate the scope of applicability and to exemplify the proposed theory.

A new technique for designing digitally tuned frequency selective analogue integrated circuits is proposed. The technique incorporates the R-2R ladder as a circuit element into the circuit design to provide precise frequency characteristics that can be tuned over a wide range. Two filters are described to illustrate the proposed approach. The proposed filters are used to implement the channel-select filter of a multi-standard direct conversion wireless receiver and the bandpass filter of a low IF frequency-hopping receiver.

An investigation is presented into the performance of a novel type of sequence estimation equalisation receiver. The receiver incorporates space diversity to further enhance the signal reception in multipath fading environments. It is shown that the receiver complexity is reduced by /spl sim/90% with virtually no performance loss compared to that of the MLSE.

Partial-band interference due to intentional and unintentional jamming in fast frequency-hopping spread-spectrum (FFH/SS) systems can be effectively suppressed by additional signal processing techniques. The authors present the performance analysis of a binary frequency-shift-keying SS system in conjunction with a fast Fourier transform (FFT) processor. The FFT-based self-normalising receiver, requiring no knowledge of signal and jamming levels, also enjoys the advantages provided by modern digital signal processing technology. Numerical results show that the receiver performance is better than that of the square-law linear combining receiver and comparable to that of the conventional self-normalising receiver as well as the clipper receiver.

An automatic frequency correction scheme for a spread spectrum communication system with a pilot channel is proposed. The results of computer simulation show that this scheme improves the performance of the mobile receiver.

The authors extend previous results (Dubey and Taylor, 1986) on an optimum receiver structure for receiving quaternary phase-shift keyed signals over a digital satellite communications channel, to include the effects of filtering following the nonlinear satellite transponder. The error performance of the receiver at low signal-to-noise ratios (SNR) is evaluated by computer simulation. An upper bound on the probability of symbol error at moderate to high SNR is also obtained. Finally, a suboptimum receiver is developed, and its performance evaluated using computer simulation. The degradation in performance of the suboptimum receiver, compared to the optimum receiver, is small.

The design of receiver architectures for use in direct sequence spread spectrum systems is reviewed. As it is difficult to construct the long matched filters for these systems, the authors propose a programmable receiver architecture which achieves the required high processing gain while, at the same time, simplifying the filter hardware requirements. Results are presented for a prototype receiver, based on digital signal processing (DSP) components, which can be reprogrammed for serial, serial-parallel or fully parallel operation while offering minimal degradation from theoretical performance.

The method for and results of a sensitivity measurement of a PSK homodyne receiver are presented. This receiver achieves phase locking of the local oscillator by means of synchronisation bits. The departure from an ideal receiver at the shot noise limit is 3.5 dB. For BER = 10−9 only 20 photon/bit are required. To the best of our knowledge, this is the highest sensitivity obtained to date with any optical communication system.

The fundamentals of radio receiver design have changed little over the last twenty years. The same, however, cannot be said for the technology used for implementation. The performance of both analogue and digital technology has revolutionised the way in which receiver design can be approached. In particular, the advent of low-cost analogue to- digital convertors and digital signal-processing devices has made possible, for the first time, the implementation of architectures once considered as unrealistic. The article addresses the design of an HF band receiver using commercially available technology, with the aim of producing a receiver whose performance is better than that available with current purely analogue designs and which incorporates a significant element of digital signal processing.

The advent of high-speed digital signal processing has revolutionised radio receiver design. The paper describes the design of surveillance receivers based on fast analogue-to-digital conversion and the fast Fourier transform. Several system architectures are discussed and the performance issues which need to be resolved in the design of a receiver are examined. These include bandwidth, dynamic range, and generation of spurious signals.

Design techniques for miniature contiguous filterbanks for use in channelised receivers operating in high pulse density environments are presented. These devices use a new prototype transfer function with a maximally flat impulse response which minimises ringing in the time domain caused by pulsed signals. The devices are designed to combine small size with high performance and good manufacturing tolerances. The devices are constructed using a hybrid of printed circuit and lumped element techniques. Measured results for 10 channel and 27 channel devices operating at a 1 GHz centre frequency with channel bandwidths of 20 MHz are presented. >

The paper describes a number of acquisition-aid schemes applicable to a tracking receiver, and discusses the relative merits of each, when applied to the proposed new split-loop tracking receiver. It is demonstrated that the more conventional designs of acquisition aid, currently in use on long-loop receivers, are less than optimum when applied to a split-loop receiver. A novel form of sweep acquisition aid, incorporating a feedback correction system, is described for application to a split-loop receiver. The operation of the system is described mathematically, along with its practical implementation and operation in an actual tracking receiver. This scheme is also shown to be applicable to conventional long-loop receivers.

The measured operating performance of a new incoherent direct-conversion receiver for high-data-rate mobile communication systems is presented. The results prove the suitability of such a receiver for the future digital European cordless telecommunication (DECT) standard.

One of the most important factors affecting the technical quality of a television picture is the amount of noise, or ‘snow’, on the picture. A television receiver produces noise if the signal from the antenna is weak, and the weaker the signal, the greater the amount of noise that is produced. Methods of predicting and measuring the signal strength are well established, but there appears to be no satisfactory reference in the literature describing what happens in the television receiver, and therefore this paper attempts to clarify and quantify the noise-related aspects of the performance of a television receiver. Following this, the study is extended to the antenna system, allowing us to show that the CCIR minimum field strengths are applicable in the context of modern receiving installations.

A ‘long loop’ v.h.f. phase-locked a.m. receiver with synchronous detector is described. The effect of the narrow-band Chebyshev i.f. filter on receiver lock-in range, hold-in range and capture time is investigated as a function of carrier level, −60 to −120 dBV, for a range of low-pass filter time-constants. The transient response of the Chebyshev filter and instantaneous limiting in the i.f. strip are shown to play a crucial role in determining the time which the receiver takes to lock onto the carrier. The receiver is not significantly more complex or expensive than sets currently in use and has the advantage that it may also be used to demodulate double-sideband diminished carrier (d.s.b.d.c.) signals.

The purpose of the paper is to show that, despite wide variations in the characteristics of currently available transistors, fully transistorized radio receivers, of an acceptable performance standard, can be mass-produced without using special techniques.An indication is given of the variations in transistor parameters which occur in production, and a typical factory test specification for a small receiver is outlined.The circuit of a 6-transistor portable radio set is used to demonstrate how the effects of variations in transistors on receiver performance can be minimized. The various factors affecting the a.f. and r.f. sensitivities, image rejection and i.f. bandwidth are discussed.

The paper describes the design considerations involved in meeting a specification for a superheterodyne receiver suitable for making subjective comparisons of amplitude and frequency modulation transmissions on very high frequencies. The reasons for the choice of particular circuits for r.f. amplifier, frequency changer, i.f. amplifier, detector, discriminator, noise limiters and audio frequency stages are dealt with in detail.

Many of the long-distance short-wave radio links between Great Britain and overseas countries are being converted from double-sideband (d.s.b.) to single-sideband (s.s.b.) operation because of the improved performance so obtained; this has necessitated new designs of s.s.b. generating equipment and radio receivers suitable for commercial operation. The type of s.s.b. transmission used incorporates two channels, each 6 kc/s wide, on either side of a reduced level pilot carrier which is nominally 26 db below the peak level of the sidebands. The function of the pilot carrier is to provide automatic gain-control (a.g.c.) and automatic frequency-control (a.f.c.) in the receiver.The equipment described includes:—(a) A drive equipment for generating a low-power two-channel reduced-carrier s.s.b. signal for subsequent amplification in the highpower stages of a radio transmitter.(b) A monitor receiver which is associated with the drive equipment and transmitter, and which enables either channel of the radio frequency (r.f.) signal at various stages in the transmitter to be demodulated to audio frequency (a.f.) for aural or electrical tests of quality and distortion.(c) Single-sideband receivers suitable for the reception of twochannel reduced-carrier transmissions, for use at the receiving station of a radio link. Receivers for single-aerial operation and triple-diversity spaced aerial operation are described.The performance requirements are stated, and the design, layout and performance of typical equipments are discussed.

The large number of frequency allocations in and around Band II compared with Bands I and III causes a serious selectivity problem in domestic combined receivers for television and f.m. sound broadcasts. The sound bandwidth of a television receiver is usually of the order of 500-1000 kc/s and since the frequency allocations of commercial radio transmitters are liable to be within 500 kc/s of the B.B.C. transmitters, interference can occur. Interference can also occur between the various B.B.C. regional transmitters whose frequency separation is usually 400 kc/s, but may be as little as 200 kc/s. The problem and a number of different solutions are discussed in detail. The circuit details of a commercially available combined receiver are then described. The sound i.f. circuits incorporate a double superheterodyne system, and the frequency of its r.f. oscillator is stabilized in Band II by means of an inexpensive a.f.c. system. Methods are described for measuring accurately the selectivity of a Band II receiver.

A simple method is described for the rapid determination at a receiver of the sense of the direction of arrival of radiation from any transmitting station. A radio bearing of the station is taken in the usual manner with a four-aerial Adcock direction-finding system, and a second observation of minimum received signal is made after certain modifications to the electrical connections between the aerials have been effected by switching. The two observations are sufficient to determine without the usual ambiguity of 180° the bearing of the transmitting station at the receiver. The method is particularly suitable for use on high frequencies and with the visual type of receiver incorporating a cathode-ray tube.

The paper describes the design of super-heterodyne receiver having very high selectivity, sensitivity and gain stability for use in the frequency band 6 to 36 kc/s. The high selectivity is obtained by means of controlled increase of Q-factor of the tuned circuits of the i.f. amplifiers, using mixed positive and negative feedback.

The purpose of the system is to provide a stereophonic signal for radio transmission within a bandwidth only slightly greater than that required for ordinary monophonic transmission. The left and right microphone signals are combined to form a single a.f. signal which is available for ordinary monophonic reception. They are also processed in such a way as to emphasize the beginnings of sounds and then utilized to form a signal, with a bandwidth of 100 c/s, carrying the directional information only. This directional signal is caused to modulate a sub-carrier at a power level much lower than that of the a.f. signal. In the receiver the a.f. signal and the directional signal are applied to a Hall multiplier unit giving the required left-loudspeaker signal as one output and the right-loudspeaker signal as the other.

Any angle-modulated system suffers from a threshold when the instantaneous noise vector becomes equal to or larger than the carrier. This effect is a limiting factor in most f.m. scatter systems, since the signal to any one receiver will fall below threshold for a far from negligible part of the time. The paper shows that the threshold level depends only on the combined bandwidth of the r.f. and i.f. circuits, and is unaffected by the existence of the frequency-compression loop. Thus, such a receiver enables one to combine the large f.m. improvement of the wide deviation signal with the low threshold of the narrow i.f. band.

The television receiving installation is susceptible to interference by three processes which can broadly be classified as follows:(a) Pick-up of interference by the aerial system,(b) Direct pick-up by the receiver circuits, and(c) Mains-borne interference introduced by connection to supply.Measurements are described which give the relative significance of these processes under typical operating conditions. The data provided on modern commercial receivers lead to the conclusion that the performance standards of the average receiver are satisfactory and that large strides to achieve immunity from interference do not involve radical development of receiver design.