is used as a common-mode choke balun[^2] and is connected directly to the terminals of the antenna with the central conductor fastened to one element and the braided shielding to the other.

The amplifier module consists of two stages that are contained in separate aluminum enclosures to reduce coupling between the low-noise amplifiers. Each stage provides 33 dB of gain for a total of 66 dB. Bandpass filtering of the signal is also performed in the second stage, and the resulting half-power bandwidth spans approximately 50 to 330 MHz. The amplifier chain can be connected through a voltage controlled three-position switch to one of three inputs: the antenna, an ambient load, or an ambient load plus a calibration noise source. Switching between the ambient load and the antenna provides a comparison to subtract spurious instrumental signals in the measured sky spectrum.

Impedance mismatch between the antenna and the amplifiers causes reflections of the sky noise within the electrical path of the instrument that produce an undesirable sinusoidal ripple in the measured spectrum due to the frequency-dependence of the phase of the reflections at the input to the amplifier. To reduce the effects of these reflections in EOR measurements, the input 