Low leakage local oscillator system

Local oscillator apparatus comprising:

• communication signal terminals for a communication signal, controlled frequency oscillator means for producing a local oscillator signal, reference frequency means for producing a reference frequency signal, feedback loop means for selecting and adjusting the frequency of said local oscillator signal relative to the frequency of said reference frequency signal, said feedback loop means including fractional-number dividing means for dividing said reference frequency by a programmable fractional number and supplying a feedback signal to control the frequency of said oscillator means, first frequency divider means for dividing the frequency of said local oscillator signal by a first division factor to produce a conversion signal, where the frequency of said conversion signal is at least approximately equal to the frequency of said communication signal, and conversion means responsive to said conversion signal for converting between said communication signal and a base-band signal,
• characterised in that second frequency divider means for dividing the frequency of said local oscillator signal by a second division factor is connected in said feedback loop means between said controlled frequency oscillator means and said fractional-number dividing means so that said fractional-number dividing means is responsive to the relative values of said reference frequency divided by said programmable fractional number and said frequency of said local oscillator signal divided by said second division factor, where the first division factor is different to the second division factor and the ratios between said first and second division factors are fractional.