There are many dipole antenna calculators available on the web... Ex.
http://www.westmountainradio.com/ant...p?frequency=69
I also found this calculator that designs multi-element Yagi style antennas.:
https://www.changpuak.ch/electronics...enna_DL6WU.php
Here is the output for a 5 element antenna cut for 69 MHz;
Code:
https://www.changpuak.ch/electronics/yagi_uda_antenna.php
Javascript Version 12.01.2014, based on Rothammel / DL6WU
-------------------------------------------------------------
Frequency : 69 MHz
Wavelength : 4348 mm
Rod Diameter : 16 mm
Boom Diameter : 25 mm
Boom Length : 3119 mm
d/lambda : 0.004 ( min.: 0.002 , max.: 0.01 )
D/lambda : 0.010 ( min.: 0.01 , max.: 0.05 )
Elements : 5
Gain : 7.99 dBd (approx.)
-------------------------------------------------------------
Reflector Length : 2110 mm
Reflector Position : 0 mm
-------------------------------------------------------------
Dipole Position : 1043 mm
-------------------------------------------------------------
Director #1 Position : 1370 mm , Length : 1991 mm
Distance Dipole - Dir. #1 : 326 mm
-------------------------------------------------------------
Director #2 Position : 2152 mm , Length : 1972 mm
Distance Dir. #1 - Dir. #2 : 783 mm
-------------------------------------------------------------
Director #3 Position : 3087 mm , Length : 1955 mm
Distance Dir. #2 - Dir. #3 : 935 mm
-------------------------------------------------------------
Directors / Parasitics are not isolated.
The length has been increased to compensate for that.
Given that the boom length is more than 10 feet, I ran another calculation looking for a frequency that allowed for use of a boom not longer than 10 feet. Here's what I came up with;
Code:
https://www.changpuak.ch/electronics/yagi_uda_antenna.php
Javascript Version 12.01.2014, based on Rothammel / DL6WU
-------------------------------------------------------------
Frequency : 70.6 MHz
Wavelength : 4249 mm
Rod Diameter : 16 mm
Boom Diameter : 25 mm
Boom Length : 3049 mm
d/lambda : 0.004 ( min.: 0.002 , max.: 0.01 )
D/lambda : 0.010 ( min.: 0.01 , max.: 0.05 )
Elements : 5
Gain : 7.99 dBd (approx.)
-------------------------------------------------------------
Reflector Length : 2062 mm
Reflector Position : 0 mm
-------------------------------------------------------------
Dipole Position : 1020 mm
-------------------------------------------------------------
Director #1 Position : 1339 mm , Length : 1946 mm
Distance Dipole - Dir. #1 : 319 mm
-------------------------------------------------------------
Director #2 Position : 2103 mm , Length : 1928 mm
Distance Dir. #1 - Dir. #2 : 765 mm
-------------------------------------------------------------
Director #3 Position : 3017 mm , Length : 1911 mm
Distance Dir. #2 - Dir. #3 : 914 mm
-------------------------------------------------------------
Directors / Parasitics are not isolated.
The length has been increased to compensate for that.
...pretty close to the center frequency of real channel 4.