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I posted a spreadsheet earlier for MW loading coils. The author of the original math stated that the calculations are dependable only to about 3 MHz.
With that disclaimer in mind, here is what that set of formulas predicts
Freq. = 13.56 MHz, Coil Form = 1.5″ diameter, 2.0″ long
|Antenna length||Element diameter||uH||Turns|
|10 feet||0.1 inches||08.25||20|
|10 feet||0.5 inches||06.30||17|
|10 feet||1.0 inches||05.50||16|
|5 feet||0.1 inches||10.75||22|
|5 feet||0.5 inches||08.00||19|
|5 feet||1.0 inches||06.60||18|
|2 feet||0.1 inches||21.00||32|
|2 feet||0.5 inches||15.00||26|
|2 feet||1.0 inches||12.00||24|
Unloaded matching 1/4 wave vertical would be 18′ high, a half wave dipole then would be around 36 feet.
http://www.k7mem.150m.com/Electronic_Notebook/antennas/shortant.html for a great HF short dipole designer