Method for neutralizing a transmitter tube

A process for neutralizing a tube of a high power digital radio broadcasting transmitter, the process comprising:

• modulating two quadrature signals I(t), Q(t) at a transmission frequency (F0) by a modulator to control a grid of the tube which is configured to work at saturation with a gain V2;
• amplifying by an amplifier a phase-modulated input signal E(t) output from the modulator, the amplifier being configured to work at saturation with a gain V1;
• predistorting the input signal E(t) by digital means so as to compensate for an undesirable coupling between an anode and the grid of the tube of the transmitter so that an output of the transmitter corresponds to a desired output signal S(t);
• determining a transfer function H(t) of the anode/grid coupling;
• calculating a corrector signal W(t) using the expression
• W(t)=jg(t)S(t)
• g ⁡ ( t ) = V2 V1 ⁢ Im ⁡ ( S ⁡ ( t ) · Y * ( t ) ) 1 - [ V2 V1 ⁢ Im ⁡ ( S ⁡ ( t ) · Y * ( t ) ) ] 2
• where Im(SIGNAL) is the imaginary part of SIGNAL,
• Y(t) is equal to S(t)*H(t), with * being the convolution product and Y(t) being a signal arising from the anode/grid coupling and being fed back to the grid, and
• SIGNAL* is the conjugate of the SIGNAL;
• and
• determining the quadrature signals I(t) and Q(t) to obtain the predistorted input signal E(t) by applying the relation
• I(t)+jQ(t)=S(t)+W(t).