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For those interested in NVIS Antennas, here is a link to L.B. Cebik’s article entitled “NVIS and ALE: Some Preliminary Studies” - https://www.antenna2.net/cebik/content/wire/nvisale.html and more specifically, to this L.B. Cebik .pdf document - An Alternative Approach to a Wide-Band NVIS Antenna System - https://www.antenna2.net/cebik/content/wire/nvis-ale-1.pdf Also, attached to this email message is an Excel worksheet I built to help those who use an Inverted-V NVIS Antenna. The worksheet makes it easy to determine the actual EFFECTIVE Wavelength Above Ground Level of Inverted-V Antennas. More details are below my signature. 73, Bob – KG5SQJ Here is why I believe an NVIS Antenna’s EFFECTIVE Wavelength Above Ground Level information is important. L.B. Cebik documented that NVIS Antennas produce their highest gain more or less straight up with the Antenna elevated to between .175 and .225 wavelengths above ground level. Obviously, an Antenna’s optimum height above the ground will vary depending on the type of ground below it and the frequency that is being used. For horizontally level antennas (flat top horizontal Dipoles, OCFD’s or horizontal Delta Loops for example), the formula to determine the Antenna’s wavelength above the ground is relatively simple: Antenna’s Elevation above ground level (in feet) divided by (300 / Frequency in MHz = (Frequency Wavelength in Meters) x 3.28084 = Frequency Wavelength in Feet) = λ above ground level. Example - Three 24’ telescoping fiberglass masts are used to elevate a flat top 40M Dipole (or a horizontal Delta Loop) Antenna to 24’ AGL. The frequency target is 7.242 MHz (the North Texas NVIS Net Frequency) and the antenna is tuned to the lowest SWR on that frequency (i.e., the antenna’s SWR Minimum of 1.12:1 [or thereabout] occurs at 7.242 MHz). 24’ / (300 / 7.242) x 3.28084 24’ / (41.425 Meters x 3.28084) 24’ / 135.9088 Feet .176589 λ above ground level (i.e., just barely inside L.B. Cebik’s documented best NVIS Antenna performance elevation between .175 λ and .225 λ) So, a flat top horizontal type antenna is fairly easy to determine its EFFECTIVE Wavelength Above Ground Level. However, Inverted-V Antennas require a bit more math because the Antenna’s height above ground level is not flat and the ends of the radiating wires are closer to the ground than the feed point at the center (or off-center) of the Antenna. According to L.B. Cebik’s article (see the link above), the formula to calculate the EFFECTIVE Wavelength Above Ground Level of an Inverted-V Antenna is as follows.