Let me offer as a reference https://www.cv.nrao.edu/~demerson/helixgain/helix.htm by Darrell Emerson, AA7FV.
FYI, Darrell is an AMSAT member and he is the only person ever to achieve ZRO level 9 (see QEX, Jan 92. pg17 or online at http://www.qsl.net/aa7fv/DSPweak.htm) by copying a weak signal sent thru AO-13 at 0, -3, -6 ... -27 dB level steps.
73 de Tom, K3IO
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