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Wire_saber
Junior Member
Username: Wire_saber
Post Number: 35
Registered: 4-2015
| | Posted on Monday, November 23, 2015 - 12:46 am: | 
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I'm aware that most hf antenna gain figures tend to be hype. Yet, after reading of the radiation lobes that are formed as the height of the antenna increases, and the different angles at which these lobes are radiated, I've become curious as to whether there is a 'standard' height at which antenna gain should be measured. At least one manufacturer links the gain figures to a height of 40'. What is the relationship between the height and gain of an antenna? Does it really vary, or is it the angle of the lobe that makes the difference? If there is a previous post with this subject, I have not been able to find it. |
Tech833
Moderator
Username: Tech833
Post Number: 2339
Registered: 8-2002
| | Posted on Friday, November 27, 2015 - 8:01 pm: |
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Most antennas are measured in "free space", which means, no ground effect is considered. If measuring gain, that's really the only way to do it.
Now, the ground has a big effect on the takeoff angle, which is the angle at which the major lobe (gain lobe) of the antenna leaves the source, headed to the ionosphere. If the major lobe heads 90 degrees out, directly at the horizon, it is said to have a 0 (zero) degree takeoff angle. If the lobe heads straight up, it is said to have a 90 (ninety) degree takeoff angle.
Generally- The higher you mount the yagi above ground, the lower the takeoff angle. You can also lower the takeoff angle by phasing two or more identical antennas mounted one over the other.
There is no perfect height, and no perfect answer.
Your radio 'Mythbuster' since 1998
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Dale
Senior Member
Username: Dale
Post Number: 2364
Registered: 12-2002
| | Posted on Friday, August 02, 2019 - 9:42 am: |
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i agree with tech 833.. if ya want a number shoot for 36 feet ...this is one wave lenth. if ya able to go even higher then go for it. just remember higher ya go more coax ya need . plus more support for tower .. still not az perfect answer but a good starting point
dale/a.k.a.hotrod
cef426
cvc#64
454 [dx numbers]
38lsb
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