A more convenient formula for a 2 wavelength half-rombic antenna is--
N = Number of full waves
Because the length is not critical the factor .025 may be dropped,
leaving the formula--
c. The half-rombic can be used for frequencies as high as three
For example, a half-rombic cut
for 30 MHz should be good at 90 MHz, which is more than enough to
cover the entire range of our VHF sets.
Typical military half-rombic antenna.