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Author Topic: “long-wire” and “inverted-L” antenna help plz?  (Read 899 times)
KC9KEP
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Posts: 208


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« on: September 11, 2009, 05:14:43 PM »

Hi,

Can someone help me understand the differences between a “long-wire” and “inverted-L” antenna?

I can find information about each but I’m not sure that I understand what the distinction is.  To make matters worse, I suspect that some hams may use the two terms recklessly.

I've built an antenna that is basically a wire that runs from the second story of my house, runs along the driveway and connects to a mast that is supported by a 5’ tripod & 10’ mast on top a shed in my back yard.

The “lead-in” runs down from the end of the antenna wire that's attached to my house and into my “shack”.

I’m not sure what kind of antenna I’ve made!

Thanks again,

--KC9KEP
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K3AN
Member

Posts: 787




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« Reply #1 on: September 11, 2009, 05:56:12 PM »

A traditional inverted L wire starts from its feedpoint near ground level, goes vertical or near-vertical for some distance and then goes horizontal or near-horizontal for the remaining distance.

If the vertical portion is longer than the horizontal portion it resembles an upside-down letter L. If the horizontal portion is longer than the vertical portion, it's more like a "sideways L."
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N5YPJ
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Posts: 642




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« Reply #2 on: September 11, 2009, 06:03:21 PM »

A long wire is at least one wavelength long and frequently multiple wave lengths long. We grew up calling any end fed wire a long wire antenna when really they were just random length end fed wires. IMO long wires will be all horizontal except for the fed wire while inverted vees will be a mixture of horizontal and vertical components. An inverted vee is usually designed to be a fraction of a wave length IE 1/4 or 3/8 wave.
Hope this helps.

Richard
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WB6BYU
Member

Posts: 13341




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« Reply #3 on: September 11, 2009, 06:19:05 PM »

An inverted L for 80 or 160m will, in fact, be a "long wire"
on some of the higher bands.

Generally an inverted L is designed around 1/4 to 3/8
wavelengths long, which puts maximum current in the
vertical section.  This makes a good low angle antenna
on the bands where quarter wave verticals are not very
convenient.  Usually they are fed against a good set of
ground radials, which are important because the feedpoint
impedance is low.

A "long wire" is, generally speaking, an end-fed wire
that is longer than 1/2 or a full wavelength (depending
on who you listen to.)  That is long enough that the
pattern is no longer predominately broadside to the wire,
but there are lobes and nulls in various directions.  Long
wires can be bent, sloping, or made into arrays like
vee beams or rhombics.  A straight horizontal wire can
be installed to point specific lobes in favored directions,
or it can simply be a wire running out to the only
available tree, and you take pot luck as to what you
can work on it.

A 1/4 wave inverted L for 160m might also be a 1.5 wavelength
long wire on 20m, with a 0.5 wavelength vertical feed
wire dropping into the shack.

If you are trying to figure out what to call your
antenna, the most important thing to remember is that
it doesn't really matter.  When in doubt, call it a
"random wire" (unless you chose a specific length for
some reason) or, "end fed wire" and let the other
station ask for more specifics if they are interested.
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K7KBN
Member

Posts: 2814




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« Reply #4 on: September 11, 2009, 06:29:47 PM »

The term "long wire" is a pretty relative one.  It refers to length in terms of wavelengths at the frequency in use.  In more traditional times, if the wire wasn't at least THREE full wavelengths long at the frequency in use, it was considered just a "random" wire.  Meaning that if you were operating on 80 meters, your antenna would have to be pretty close to 800 feet long to "qualify" as a long wire.

As stated earlier, an end-fed one-wavelength wire for 80 meters (around 260 feet) would be a true long wire for 20 meters and above.
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73
Pat K7KBN
CWO4 USNR Ret.
AA4PB
Member

Posts: 12899




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« Reply #5 on: September 11, 2009, 07:17:43 PM »

Just call it a "random end-fed wire" unless you've cut it to some special length like 1/2 wavelength. If so then call it an end-fed 1/2 wave wire. It's probably not long enough to be considered a true "long wire" and it's not really configured as an "inverted-L".
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K0ZN
Member

Posts: 1553




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« Reply #6 on: September 11, 2009, 09:01:06 PM »

Hi.

You did not give the total length of the wire, so we can only guess, but unless you have a couple of hundred feet in the horizontal run of wire, you have, as other noted, either an "end fed wire" or a "random wire".

TRUE "Long Wire Antennas" are usually configured in a specific direction to take advantage of the gain (and there is real gain in those systems) from the lobes. The most effective types are typically V beams (two truly long runs of wire) in a fairly narrow V configuration and the well known Rhombic antenna. Multi wire long wires function by COMBINING lobes from the different wires to give more gain.

Long wires can be terminated in a resistor to make them directional in ONE direction. When they are unterminated, they are typically bi-directional.

When I was in the Army Signal Corps, we had a MARS station with a "V beam" that was 1,200 ft. on each leg oriented towards Vietnam; it was an excellent point-to-point antenna. In addition to a very narrow beam width and high gain, it had excellent "space diversity" which greatly reduced fading. Large Long Wire Systems are awesome antennas, but take a LOT of real estate. They are also kind of hard to rotate.

You can improve the radiation efficiency of your antenna by installing a few "radials" immediately under the antenna. This helps reduce ground losses some and seems to stabilize the impedance; as the amount of moisture in the soil changes, the Z of the antenna will change a little and you will have to tweak the tuner; the wires under the antenna will reduce that. The ground system is a significant part of your antenna system, so the better and more elaborate it is the more of your transmitter power will be radiated. I have used end fed wires like yours a couple of times and my experience was that a "crow's foot" of about 7 wires (fanned out about 18" to 24" apart at the far end) under the antenna makes a bigger difference than theory says it should...and is worth the effort if you can do it. Ground rods are totally worthless for RF grounds for the antenna; they will provide "ground" for your tuner to work against, but their effect is essentially to dissipate power, not radiate it. Your system WILL work without the "radials" but it will be more efficient with some...or an elaborate ground.

73,   K0ZN
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