Abstract: A receiver estimates I/Q imbalance in I and Q input signals using circuitry to separate different frequency components of the I and Q input signals, and estimation circuitry arranged to estimate I/Q imbalance at the different frequency bands. The separating of the bands may be carried out in the frequency domain, and may involve combining corresponding values representing corresponding negative and positive frequency bands, and converting the separated frequency domain representations to a time domain representation before the estimation. The estimated imbalance may be used to correct the I and Q signals at the different frequency bands.

Abstract: A receiver estimates I/Q imbalance in I and Q input signals using circuitry to separate different frequency components of the I and Q input signals, and estimation circuitry arranged to estimate I/Q imbalance at the different frequency bands. The separating of the bands may be carried out in the frequency domain, and may involve combining corresponding values representing corresponding negative and positive frequency bands, and converting the separated frequency domain representations to a time domain representation before the estimation. The estimated imbalance may be used to correct the I and Q signals at the different frequency bands.

Abstract: Radio transceivers 5 in a communication system periodically broadcast signal pulses 6 to enable a radio transceiver 5 to determine their proximity. Each radio transceiver 5 has a clock 16 for maintaining a time synchronised by a synchronisation means 17 via the Global Positioning System (GPS). Each radio transceiver 5 transmits a signal pulse 6 at the same point in the synchronised time. A signal detector 19 detects the start of a signal pulse 6 received from the closest radio transceiver 5 and a proximity estimator 20 estimates the proximity of the closest radio transceiver 5 by determining the difference between the point in the synchronised time at which the signal pulses 6 are broadcast and the point in the synchronised time at which the start of a signal pulse 6 received from another radio transceiver 5 is detected.

Abstract: A radio transceiver capable of transmitting and receiving on a common radio channel in a half duplex mode includes a direct conversion transmitter and a low IF receiver. A common signal generator (2, 2?, 2?) comprises a first and second frequency generator (40, 41). The first frequency generator generates a carrier frequency signal which is used by both the transmitter and receiver. During reception, the second frequency generator generates an offset signal at the low IF frequency which is mixed with the carrier frequency signal to form a down conversion signal. During transmission, modulation is applied either directly to the carrier frequency signal in one embodiment, or to the offset signal which is then mixed with the carrier frequency signal to form a modulated carrier frequency signal in another embodiment.

Abstract: A slave radio transceiver for use in a frequency hopping radio system synchronizes by receiving on a sequence of simultaneous combinations of radio channels until a paging message is received from a master transceiver, and may then revert to single channel frequency hopping operation. The slave's multi-channel receiver is sub-equipped to receive simultaneously on a only sub-set (PF12, PF13) of the channels within its bandwidth, the received channels being selected by independent programming within the bandwidth. The channels received simultaneously may be selected to correspond to different degrees of misalignment between the master and slave.

Abstract: An RF circuit configured to inteface a balanced port (1, 2, 11, 12) with an unbalanced port (4, 14) by emulating the function of a balun. Reactive components (20, 30, 120, 130) in both branches of a balanced circuit form two resonant circuits by resonating with parasitic reactance. At a predetermined operating centre frequency, one of the two resonant circuits is above resonance and the other is below resonance, resulting in a 180° phase difference between the signals delivered by the two branches. When used to interface an unbalanced signal source (10) to a balanced load (40), the input impedance may be set to a real value matching the output impedance of the signal source by selection of the reactive component (20, 30) values.

Abstract: A receiver with an integrated mixer/Sigma-Delta Modulator configuration for digitizing a relatively low-bandwidth signal modulated on a high-frequency carrier, for example in a radio receiver. The Sigma-Delta Modulator has an continuous-time loop filter (F1, F2) with anti-aliasing characteristics which eliminate the need for a separate lowpass filter between the mixer (MX) and the Sigma-Delta Modulator.

Abstract: An RF circuit configured to inteface a balanced port (1, 2, 11, 12) with an unbalanced port (4, 14) by emulating the function of a balun. Reactive components (20, 30, 120, 130) in both branches of a balanced circuit form two resonant circuits by resonating with parasitic reactance. At a predetermined operating centre frequency, one of the two resonant circuits is above resonance and the other is below resonance, resulting in a 180° phase difference between the signals delivered by the two branches. When used to interface an unbalanced signal source (10) to a balanced load (40), the input impedance may be set to a real value matching the output impedance of the signal source by selection of the reactive component (20, 30) values.

Abstract: A radio transceiver capable of transmitting and receiving on a common radio channel in a half duplex mode includes a direct conversion transmitter and a low IF receiver. A common signal generator (2, 2′, 2″) comprises a first and second frequency generator (40, 41). The first frequency generator generates a carrier frequency signal which is used by both the transmitter and receiver. During reception, the second frequency generator generates an offset signal at the low IF frequency which is mixed with the carrier frequency signal to form a down conversion signal. During transmission, modulation is applied either directly to the carrier frequency signal in one embodiment, or to the offset signal which is then mixed with the carrier frequency signal to form a modulated carrier frequency signal in another embodiment.

Abstract: A slave radio transceiver for use in a frequency hopping radio system synchronises by receiving on a sequence of simultaneous combinations of radio channels until a paging message is received from a master transceiver, and may then revert to single channel frequency hopping operation. The slave's multi-channel receiver is sub-equipped to receive simultaneously on a only sub-set (PF12, PF13) of the channels within its bandwidth, the received channels being selected by independent programming within the bandwidth. The channels received simultaneously may be selected to correspond to different degrees of misalignment between the master and slave.

Abstract: A power amplifier suitable for use in n communication transmitter/transceiver which transmits bursts of signals in accordance with a TDD or TDMA protocol. Shaping the leading and trailing edges of the transmitted bursts is done using a feedback control loop around a substantially linear power amplifier (22). A modulated signal to be amplified is multiplied by an output of the control loop using a multiplier (28) and the product is applied to the power amplifier (22). A portion of the amplified signal is applied to a detector (38), the output of which is applied to one input of a difference amplifier (42), a second input of which receives a step-like reference signal of a predetermined amplitude. The difference signal produced is integrated (46) and low pass filtered (48) or vice versa, which slows down the difference signal to provide an output signal of the control loop which has the desired leading edge shape.

Abstract: A system for producing a digital representation of the value of an angle .theta., typically a phase angle, from two analog input quantities representative of A sin .theta. and A cos .theta., where A is an amplitude factor, comprises logarithmic amplifiers (IC1-IC4) which produce analog representations of a plurality of quantities (sin .theta., cos .theta., sin (.theta.+3.pi./4), cos (.theta.+3.pi./4)) derived from the two input quantities and which are arranged to add or subtract their outputs to produce quantities (V.sub.1 -V.sub.4) which are independent of A and the value of each of which lies within a predetermined range (-C to +C) in at least one respective portion (2.pi./n) of an angular range for .theta. of 2.pi. radians. The digital representation of .theta. is the concatenation of digital representations of the angular portion (2.pi./n) in which .theta. lies and of the value of .theta. within the portion that is derived from the selected appropriate one of the quantities V.sub.1 -V.sub.