A variable tuning transceiver sealed in a protective housing, such as a bolus, is adjusted to transmit a near optimally tuned signal at a select frequency while in vivo in an animal. More specifically, the variable tuning transceiver provides a plurality of incident power transmissions over an antenna at a plurality of corresponding different capacitance levels as defined by a variable tuning circuit in the transceiver. A detector circuit, also in the transceiver, detects reflected power for each of the incident power transmissions conditioned at each capacitance level which is affected by the dielectric constant in the animal and any mismatches in the antenna. Each reflected power can then be stored in nontransient memory in the transceiver whereby the microprocessor, also in the transceiver, can select the capacitance level with the lowest reflected power found and therefore the strongest external signal from the capacitance levels sampled. Once selected, transmissions which include data from sensors within and on the animal are transmitted externally to an external receiver.