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Author Topic: Antenna heights above ground  (Read 4189 times)
KK4PVQ
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Posts: 14




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« Reply #15 on: April 26, 2013, 06:44:42 PM »

Thanks for the info
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KQ6Q
Member

Posts: 976




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« Reply #16 on: April 26, 2013, 10:01:03 PM »

If the vhf vertical has built-in radials (a ground plane) or doesn't need them (like a j-pole) what matters is how far the antenna can 'see' - how far is it to the horizon.  If you raise it to clear a building or other nearby obstacle (a hill), it will make a difference, otherwise height won't matter very much. High is good, but a lot higher won't be too much better.
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WB6BYU
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Posts: 13243




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« Reply #17 on: April 27, 2013, 09:06:07 AM »

Actually the added height DOES make a difference, although once a signal is full scale
we rarely notice the added signal strength.

This was brought home to me over a line-of-sight path (of about 20 feet) when
I could measure around 20dB difference as I moved my 2m yagi from near the ground
to as high as I could reach, even though it had a direct view of the transmitter
antenna (about 6' high in a tree) the whole time.

Over flat ground at a distance of 10 miles on 2m, EZNEC predicts an improvement of
nearly 4dB when an antenna is raised from 20' to 30' above ground, and more than
2dB more going to 40'.  At those heights, doubling the height is equivalent to 4 times
the transmitter power (besides also improving receive.)

But for most hams the world isn't that flat, and even small undulations in the ground
that we might not notice while driving (unless we are are monitoring signal strength,
as some of us have occasion to do) will cause significant differences.  In those cases
height will make even more of an improvement because it allows the signal to clear
obstructions due to terrain, buildings, etc.

You might not notice any difference in the local repeater, and often getting the
antenna above the roof is sufficient for most FM communications.  But raising
an antenna by 10 or 20 feet can make a significant improvement on weak signals.
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KK4PVQ
Member

Posts: 14




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« Reply #18 on: April 28, 2013, 03:39:07 PM »

I think mine is doing pretty good, I went through all my repeaters , and can hit 27 of them...out to about 125 miles at most, seems to be a pretty good radius too..there is many I don't get but I guess some could be turned off, not in use or terrain issue...I downloaded from RT systems program and found city names do not always match up with what the program states, and a couple share the same freq..not complaining just noticed it
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KB6HRT
Member

Posts: 106




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« Reply #19 on: April 28, 2013, 06:11:08 PM »

Found this out years ago, had access to a bucket truck, had a Yagie TV antenna used the BT it to raise and lower the antenna and found the best height where the antenna performed the best at my QTH for one station and height for all the stations it would receive, could have raised the antenna another 15+ ft more or lowered it about 25 ft, I called the place where my reception was the best, the sweet spot for that antenna. There are so many thing that can change even what I did its crazy, but a rule of thumb
is raise the antenna so it pulls in the stations you want well and leave it at that, if you raise the antenna higher you signal to noise will drop some, you will be lower your volumn so there less back ground noise, also the higher the antenna the more wind load the antenna an pole will have, if your looking for long range ground wave then higher is better......for what ever that is worth............KB6HRT
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KK4PVQ
Member

Posts: 14




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« Reply #20 on: April 28, 2013, 06:23:19 PM »

I hear ya..where I have it now meets my goal and some so I am leaving it alone.
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