serial port of the computer, are enclosed in an aluminum box to prevent self interference.

The Measured Spectrum {#s_data_acquisition}
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![ \[f\_edges\_spectrum\] Integrated spectrum used for upper limit analysis of reionization signal. The sky temperature, $T_{sky}$, is an estimate based on modeled values for cable losses and no correction for antenna reflections. The spectrum represents the best 10% of the data from observations over two nights. It is selected by discarding individual observation cycles (see § \[s\_data\_acquisition\]) containing periods of particularly intense radio frequency interference. A total of approximately 1.5 h of integration is included (3.75 h including the ambient load and calibrator noise source measurements in each cycle). The black curve shows the spectrum after de-weighting the interferers (shown in gray) present in the retained observations.](f3.eps){width="22pc"}

The measured spectra from each of the three switch positions can be combined to produce a calibrated estimate of the true sky spectrum. The three spectra are given by $$\begin{array}{ccl}
p_0 & = & g ~ (T_L + T_R) ~ (1 + n_0) \\
p_1 & = & g ~ (T_L + T_R + T_{cal}) ~ (1 + n_1) \\
p_2 & = & g ~ (T_A + T_R) ~ (1 + n_2)
