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Old 9-Aug-2019, 6:48 PM   #7
GroundUrMast
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Join Date: Oct 2010
Location: Greater Seattle Area
Posts: 4,750
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.
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Last edited by GroundUrMast; 9-Aug-2019 at 10:46 PM. Reason: Added Yagi example
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