How high is my antenna?

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Tigersaw
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How high is my antenna?

Post by Tigersaw »

I'm not asking you to be a mind reader, but curious as to what figure you give if asked the question.

Now I give the height of the base (in this case an Antron) which is about 20-25 feet - but this means the tip is 40 feet above ground, so bit of a difference if I was to use that figure.
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ch25
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Re: How high is my antenna?

Post by ch25 »

You always tell feedpoint height.
Simple example. My 80m vertical is 23 meter high, but feedpoint is 2m over the ground. So my antenna is 2m over the ground, not 25 xD
You can't have too many antennas...
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Re: How high is my antenna?

Post by wa10 »

i always use the length of the mast/pole for anything end-fed, i do the same for starduster & gain-master, my GM is on a 35ft or so scaffold pole about 1 wavelength above a field,
the only cb antenna i have that i don't see that way is the astroplane which is only 1/2 of an antenna as it comes in the box.
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
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The Collector
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Re: How high is my antenna?

Post by The Collector »

I've always said that my aerial is *** feet to the tip. As far as I'm aware the whole thing radiates, so if up to the tip does, that's how tall it is.

Plus it sounds much better when you're talking utter sh**e in the pub ;)
ian
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Re: How high is my antenna?

Post by ian »

The feed point
De Ian 108SD121 - 108ID121 - 108OP121.
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Re: How high is my antenna?

Post by theEarwigger »

The height of any vertical antenna is the "effective height".

But that's buried in a 100 page antenna book!
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Re: How high is my antenna?

Post by wa10 »

Technically speaking that's correct, effective height is the thing that effects your signals the most,

Effective height is your height of current maxima or centre of radiation where your antenna has the strongest radiation,

for none loaded antennas which covers most cb base antennas,
1/2wave dipoles 1/2wave & 5/8waves end fed antennas, current maxima is 1/4wave down from the tip of the antenna ,

for loaded antennas like hat loaded avanti astroplanes current maxima is at the hub 4ft from the tip, which give them an advantage in height of current maxima or effective height when you are subject to FCC height restrictions,

5/8 gain-master has two current maximas, 1/4wave down from the tip & 1/4wave up from the choke,

height of current maxima is what gives a 5/8wave some gain over a 1/2wave,
but raise an efficient 1/2wave up to same tip height & it has a little more low angle gain than a 5/8wave,

if a local asked how high my antenna was & I replied with "my antennas effective height is 49ft",
they would have no idea I was talking about.

If I say " im running a 1/2wave silver rod on a 40ft pole"

then people who don't understand effective height & current distribution in antennas know how high your antenna is,
& people that do understand current distribution know its effective height is about 9ft higher than that.
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
wa10
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Re: How high is my antenna?

Post by wa10 »

i should add that effective height effects your antennas gain at low angles the most when the antenna is doing ALL or almost all of the radiating & receiving,

even more so when you don't live in an open field & that extra height of current maxima also gets you over obstructions.

BUT a typical cb antenna install can often have even more of an effect on your signals & local noise than its effective height if you pick or cause by ground wire a low common mode impedance,

and never in a good way

once all antennas are installed correctly isolated at the same tip height many people would surprised even AMAZED as i was myself how little difference there is between any of them including A99's.

a 5/8 waves extra low angle gain vanishes.
W8JI
"An antenna with a poor ground using few radials cannot have a support mast grounded to the radial common point (at least it shouldn't if designed properly) There is no exception to this!
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andrew013
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Re: How high is my antenna?

Post by andrew013 »

i just say my ariel is 24 ft long on a 21 ft pole 35 ft off the ground
on air,tyne&wear,northumberland,durham,holy island,eu120+eu124 and anywhere from gateshead/north wales
scrap uk 40 give cbers L/M/Hcalling on 27.355/555 usb qsy 27.015 lsb/410 usb cb radio is for life not just for profits
i do cb radio not 11mtres,countrys worked 2015 with imax 2000 72
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