A method (and apparatus) of receiving (and/or transmitting) a wanted
modulated radio frequency signal with reduced locally generated noise. In
the case of reception, the method comprises the steps of receiving a radio
frequency signal 99; generating a high frequency local oscillator signal
71,72, which can be mathematically described as having a fixed frequency
.omega..sub.RF responding to the frequency of the carrier wave of the
wanted modulated radio frequency signal and a phase .phi..sub.SS which
varies in time according to a predetermined local phase function; mixing
the received radio frequency signal 99 with the high frequency local
oscillator signal 71,72 to generate a mixed signal 111,116 so as to spread
locally the band-width of the signal with which it is mixed. The mixed
signal is then converted from an analogue signal into a digital signal
121,122. A low frequency local oscillator signal 61,62,63,64 is generated,
which can be mathematically described as having a fixed frequency of zero
and a phase .phi..sub.SS which varies in time according to the
predetermined local phase function when delayed by a predetermined delay
corresponding to the time taken for the signal to propagate between the
first mixing step 110,115 and the second mixing step 300. The mixed signal
is mixed with the low frequency local oscillator signal to recover a
recovered signal 131,132 including both a despread wanted base-band signal
whose phase is not dependent on the predetermined local phase function and
a spread noise signal whose phase is dependent upon the predetermined
local phase function. In the case of transmission, the signal to be
transmitted is spread locally by a low frequency local oscillator signal
and subsequently mixed in the transmitter with a high frequency local
oscillator signal to recover a recovered signal including both a despread
wanted RF signal whose phase is not dependent on the predetermined local
phase function and a spread noise signal whose phase is dependent upon the
predetermined local phase function.
