Abstract: A mobile antenna circuit for resonant transmitting from an RF signal source may comprise: an antenna having a base and at least first and second conductive sections one of which is extendable and retractable to lengthen and shorten the antenna; a motor operatively connected to one of the conductive sections for extending and retracting the antenna in response to control signals thereto; an impedance matching circuit coupling the RF signal source to the base of the antenna for matching impedance thereof at a specified frequency; and control components connected to the motor to produce control signals for extending and retracting the antenna section so as to resonantly tune the antenna at a specified frequency. The circuit may include a phase angle detector connected between the RF signal source and the impedance matching circuit for developing a voltage differential being fed to the control components for producing the control signals for extending and retracting the antenna section.