What is the Maximum Range I can Get?

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@abcd567

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The default value of refraction on heywhatsthat site is 0.14, but you have specified refraction=0.25. I am not sure, but feel this is due to slight difference in propagation parameters of Light waves & Micro waves, and will cover for difference between optical and radio horizons (For microwaves, the radio horizon is farther than optical horizon by say 50 nautical miles or so).

Yes. See the note at the end of this post: post183592.html#p183592