Apparatus for low power radio communications

A transmitting means for efficient low power radio communication, the transmitting means operates with a certain frequency modulated frequency deviation over a certain carrier frequency range, comprising:

• a) DC cancellation mid-point modulation means utilizing a DC compensating signal having a non-modulation state and a modulation state such that said DC compensating signal changes from said non-modulation state to said modulation state upon commencement of modulation and remains in said modulation state so long as modulation continues, and a data signal having a DC voltage content which swings between end points around a nominal mid-point, and having a state prior to modulation commencing opposite to the state of said DC compensating signal:
• b) resistive summing circuit which sums said DC compensating signal and said data signal such that the component in the sum due to said DC compensating signal cancels the change in the DC content of the component in the sum due to initiation of modulation by said data signal resulting in a DC cancellation mid-point modulation output whereby the commencement of data modulation begins from said nominal mid-point between said end points of said DC voltage content swing of said data signal and such that there is no change in the average DC level of said DC cancellation mid-point modulation output in said non-modulation and modulation states;
• and
• c) frequency synthesizing means incorporating said DC cancellation mid-point modulation means and further comprising a phase locked loop circuit, having open and close loop conditions, with a voltage controlled oscillator having an VCO output of variable frequency, and a loop filter/sample and hold circuit, said loop filter/sample and hold circuit switches said phase lock loop circuit between said open loop and close loop conditions, such that said output signal remains stable and substantially on frequency when said phase locked loop circuit is in said open loop condition, with a minimum of frequency drift over a period of time and whereby said DC cancellation mid-point modulation means causes the frequency deviation of the frequency modulation to vary approximately equally around the desired carrier frequency over which said transmitting means may operate.