1005 ÷ fmhz. is the formula for a full wave driven loop element, not a straight full wave element. the formula for a full wave loop reflector element is 1030 ÷ fmhz.. 492 ÷ fmhz. is the formula for a center-fed 1/2λ dipole or an end fed 1/2λ vertical over real earth ground. as mentioned by groundwire earlier, 492 X 0.95 = 467.4 or 468 which is the free space formula conversion from the over real earth ground formula.

an antenna is in free space when the real earth ground beneath the elevated antenna has no affect or influence over the manner in which the antenna operates. using the free space formula for calculating antenna length for antennas that are not in free space will result in resonant operating frequencies higher than your intended operating frequency.

as the distance between real earth ground and the antenna decreases, increased capacitive coupling between the earth ground and the antenna decreases the electrical length of the antenna, driving the resonant operating frequency higher as a result.

capacitance induced or coupled into an antenna electrically shortens the antenna and raises the operating frequency.

inductance induced or coupled into an antenna electrically lengthens the antenna and lowers the operating frequency.

when the antenna is adjusted for (X) reactance = 0 @ any given frequenc/y/ies then all formula and velocity factor error is eliminated. these errors are generated by the λ to diameter ratio of the conductors used, i.e., wire vs. tubing, end effect and proximity to real earth ground.

cut any dipole for a given frequency using the 468 formula, place the feedpoint up @ 1/4λ above real earth ground and then using an analyzer, scan the band until you find the frequenc/y/ies where X = 0 and compare that to the frequency that you originally cut the dipole to operate at.

YDRC

maybe this will help:

https://duckduckgo.com/?q=492+÷+frequency+in+mhz.+=+length+in+feet++&t=h_&ia=web
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