Not easily done. It is usually measured on an antenna range, by noting the two azimuths where the gain is 3 dB down from the max; these two points are also called the half-power points.
Now maybe some more about overload:
WEVV has a Noise Margin of 56.8 dB. If you add the 10.5 dB gain of a Winegard HD7694P, that brings you up to 67.3 dB; that's OK.
Interpreting Noise Margin in the TV Fool Report
http://www.aa6g.org/DTV/Reception/tvfool_nm.html
WEVV has a signal power of -34.0 dBm = 15 dBmV
The CM7778 has a max input of 34 dBmV
WEVV 15 dBmV + 10.5 dB ant gain = 25.5 dBmV; OK
WEVV -34.0 dBm + 10.5 dB ant + preamp gain 16 dB = -7.5 dBm; close to tuner overload
ATSC Recommended Practice:
Receiver Performance Guidelines
Document A/74:2010, 7 April 2010
RECEIVER PERFORMANCE GUIDELINES
5.1 Sensitivity
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A DTV receiver should achieve a bit error rate in the transport stream of no worse than 3x10E-6 (i.e., the FCC Advisory Committee on Advanced Television Service, ACATS, Threshold of Visibility, TOV) for input RF signal levels directly to the tuner from –83 dBm to –5 dBm for both the VHF and UHF bands.
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5.2 Multi-Signal Overload
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The DTV receiver should accommodate more than one undesired, high-level, NSTC or DTV signal at its input, received from transmission facilities that are in close proximity to one another. For purposes of this guideline, it should be assumed that multiple signals, each approaching –8 dBm, will exist at the input of the receiver.
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