A digital telemetry transmitter for transmitting eight channels of diagnostic quality electrocardiographic data has input circuitry for receiving analog EKG signals originating at electrodes on the patient. The input circuitry includes a circuit for ascertaining the impedance of the electrode connection to the patient and to indicate an electrode fault. EKG signals from the input circuit are provided to a digital/analog converter for converting the analog signals into corresponding digital signals. The analog/digital converter may comprise an eight channel, 20-bit converter, sampling the input signals at a frequency of 10 KHz and providing a digital output signal having a frequency of 500 Hz. The output of the analog/digital converter is provided to a microprocessor control which provides a digital EKG modulating output signal. The output signal is periodically inverted to avoid stationarity in the transmitted data. The output signal includes error correction data that enables a receiver for the transmitted data to correct the digital EKG signal for noise. The microprocessor control changes the resolution of the transmitter when large signal changes occur in the data to accommodate such signals and to provide data compression. An rf signal generator generates an rf carrier signal. The modulating output signal of the microprocessor control is provided as a frequency modulating signal to the rf signal generator. The rf signal generator is stabilized against alterations due to reflected antenna loading.