Abstract: A modulator 200 is based around a switching circuit 212 and a pausey stub balun 210. The balun 210 has a distributed resistance 232 to ground. The balun may be implemented as a strip line device (FIG. 5b).

Abstract: A distortion compensating apparatus for use in IQ modulation and demodulation techniques wherein a first distortion arrangement distorts the I-signal by adding to the I-signal a first weighted function of the I-signal and a first weighted function of the Q-signal and a second distortion arrangement distorts for Q-signal by adding to the Q-signal a second weighted function of the I-signal and a second weighted function of the Q-signal, such that the weighted functions of the I-signal are independent of the Q-signal and the weighted functions of the Q-signal are independent of the I-signal. This enable distortions to be compensated in both sidebands of the IQ modulated signal.

Abstract: A spectrum analyser that includes means (8) for converting, at each of a series of frequency settings, a received radio frequency signal into an intermediate frequency signal, each intermediate frequency signal being derivable from more than one nominal received radio frequency signal. The spectrum analyser carries out a frequency analysis (14) of each intermediate frequency signal to produce a power spectrum thereof and constructs a composite received radio frequency signal power spectrum corresponding to each intermediate frequency signal power spectrum. The composite radio frequency signal power spectrums are then operated on by the spectrum analyser to provide the actual power spectrum of the received radio frequency signal.