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Author Topic: VHF/UHF height vs. feedline loss question  (Read 686 times)

AF5CC

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Re: VHF/UHF height vs. feedline loss question
« Reply #15 on: May 17, 2022, 08:07:24 AM »

Thanks for bringing this topic up. I was thinking about this very topic the other day-is there a point of diminishing returns for VHF/UHF, where feedline loss outweighs any increased advantage in height you get.  Sounds like there isn't.

Along a related line, how does increasing height play for HF, especially for lower heights?  If you have a tribander miniyagi at 15 feet, which I know is too low to be really effective but that is where it is, would raising it to 25 feet really increase performance?  It is still below a half wavelength high on 20 meters, but would that extra 10 feet of height significantly improve performance on all of the bands?

73 John AF5CC
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W1VT

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Re: VHF/UHF height vs. feedline loss question
« Reply #16 on: May 18, 2022, 02:38:04 PM »

HFTA that comes with ARRL Antenna book will calculate horizontal antenna patterns with terrain interaction.
k6tu.com can provide free terrain data.  Microdem is no longer a useful program for most hams as the government database has changed.
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W9IQ

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Re: VHF/UHF height vs. feedline loss question
« Reply #17 on: May 18, 2022, 03:02:43 PM »

I would use some coverage modeling software to see what the additional height minus the coax loss does for you. Here is a nice site that is totally free that I have used for several repeater installations: https://www.ve2dbe.com/rmonline_s.asp. You can easily model the two situations with their respective antenna gains, coax losses and antenna heights and compare the results.

- Glenn W9IQ

Even though you are an amateur, analyze it like a professional.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

RFRY

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Re: VHF/UHF height vs. feedline loss question
« Reply #18 on: June 07, 2022, 02:38:16 AM »

Below are images from a set of PPT slides showing possibly more important elements than antenna height and feedline length in the performance of point-point terrestrial links at VHF and above.

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KB1GMX

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Re: VHF/UHF height vs. feedline loss question
« Reply #19 on: June 08, 2022, 09:25:32 AM »

RFRY,

One factor not covered and often significant is trees.  They are obstructions,
scatterers, and attenuators depending on height and frequency..  At VHF
maybe an amalgam of all three.

However often the signal gets through despite all that.

Allison
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