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Author Topic: Gain of long wire antenna compare with dipole  (Read 1545 times)

DELETED_VR2UKQ

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Gain of long wire antenna compare with dipole
« on: September 14, 2019, 10:17:16 AM »

How is Gain and other 'effectiveness factors' of single-wire long wire antenna, with antenna tuner (ICOM AH-4 type), compare with single frequency or multiple frequencies dipole HF antenna?

What is practical range of length of long-wire, for fixed home station?

73 Simon VR2UKQ
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AA4PB

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RE: Gain of long wire antenna compare with dipole
« Reply #1 on: September 14, 2019, 12:17:22 PM »

An antenna isn't really classified as a long wire unless it's at least several wavelengths long on the frequency of use. A real long wire will have gain over a 1/2 wave dipole close to the ends of the wire. Most end fed antennas are not long enough to perform as a true long wire and they perform very similar to a 1/2 wave dipole.

You have to be careful with the AH4 and similar SGC tuners in that they will have difficulty matching when the wire length is close to 1/2 wavelength or a multiple due to the very high feed impedance. The SGC manuals give some recommended wire lengths to use with their tuner to ensure a good match. I've also found that it pays to stay away from an exact odd multiple of 1/4 wavelength on any band you use because the low feed impedance will increase the loss in your radial or counterpoise system if it is less than ideal.
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Bob  AA4PB
Garrisonville, VA

G4AON

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RE: Gain of long wire antenna compare with dipole
« Reply #2 on: September 20, 2019, 07:54:52 AM »

Download the demo version of EZNEC and see for yourself.

Height above ground has a huge effect on performance of both a dipole and an end fed wire.

Generally signals from stations using end fed wires tend to be mediocre compared to those running well sited dipoles, it has more to do with “put up any old wire and hope it works”, rather than anything inherently bad about an EF wire. You can feed a “dipole” at the centre or end and it makes no difference to the radiation pattern, except for issues with feeder radiation being more difficult to avoid with an EF wire.

73 Dave
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WA7ARK

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RE: Gain of long wire antenna compare with dipole
« Reply #3 on: September 26, 2019, 11:05:51 AM »

Download the demo version of EZNEC and see for yourself...
I'll second that advice...

There are two kinds of wire antennas: Hertz and Marconi

Hertz antennas are self contained (they would work in free space). This includes dipoles, Off-Center-Fed (with a 1:4 transformer) and End-Fed-HalfWave antennas (with a 1:49 transformer). Best mounted horizontally, as far away from dirt as possible.

Marconi antennas rely on being coupled to dirt. Dirt is lossy, so its conductivity must be enhanced by running wire in/on the dirt (radials). Alternatively, the Marconi has to provide its own "dirt" by using an elevated "ground plane", consisting of several radial wires parallel to the dirt, but elevated high enough to avoid some of the dirt-induced losses. This includes verticals, inverted-Ls and the kind of "random length wires" you are asking about. They cannot be a multiple of a half-wavelength on any band you expect to use them on.

I have never had a Marconi antenna that works as well as a Hertz
« Last Edit: September 26, 2019, 11:11:32 AM by WA7ARK »
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Mike, WA7ARK

WB6BYU

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RE: Gain of long wire antenna compare with dipole
« Reply #4 on: October 04, 2019, 04:54:20 PM »

Quote from: SIMON123

How is Gain and other 'effectiveness factors' of single-wire long wire antenna, with antenna tuner (ICOM AH-4 type), compare with single frequency or multiple frequencies dipole HF antenna?

What is practical range of length of long-wire, for fixed home station?




Gain and radiation pattern are both a function of the wire length in wavelengths.
A half wave end-fed wire has a broadside pattern, just as if it was fed in the center as a
dipole.  A full wavelength has major lobes at about 45 degrees to the wire (all around
the wire) and a null broadside to it.  As the wavelength gets shorter (frequency is higher)
maximum radiation will shift more towards the end of the wire, with various nulls and
weaker lobes in other directions.  That assumes the wire is horizontal.

A sloping wire can give some gain if you align the angle of radiation from the wire
for that frequency with the angle of the wire.  This primarily gives vertically polarized
radiation.

Typically when I set up such an end-fed wire, I aim the end in my desired direction for
longer paths on the higher frequency bands, and use it for NVIS (nearly omnidirectional)
local contacts on 80m.  This works as long as the wire is 1/2 wavelength on the frequency
you want to use for NVIS:  with a 40m long wire, 80m NVIS works well, but on 40m there
is an overhead null in the pattern, so it isn't as good for close contacts when the band is
open.  When I had an 80m long wire, it worked great for local contacts on 60m, but was
marginal on 80m.  Then one night after a net another station called me and asked if I was
using an amplifier:  the high angle radiation off the ends was particularly effective at 500 -
800 km, even if the antenna didn't work as well for stations out to 100 km.


Can you make a wire too long?  Certainly, if in doing so it doesn't meet your objectives
for radiation pattern.  The 80m long wire didn't work as well for me as a wire 40m long,
both due to the 80m coverage, and because the pattern on 15m and 10m got too sharp,
so it wasn't as good for general operation.  But if you want to optimize for a specific direction
and have supports that can run it nearly in that direction,  you can choose an optimum
length to focus it where you want.  (And you can get more creative by carefully putting a bend
in the middle of the wire to make the equivalent of a vee beam, but that gets more complex.

I knew one station who had good results with a 400 foot (130m) long wire, particularly on
40m and 80m.  (At least, she had a good signal at my location - I don't know where the
other lobes ended up.)  I put up a 200m wire one year for Field Day, and it was spectacularly
poor, perhaps because it angled down a hill.  (The best thing about that antenna was asking
a particularly annoying person to go untie the other end of it, without telling him how
far down the hill it ran...)

I have used many such antennas over the years, particularly when I had only a single far
support for it.  If you can point it in a useful direction, it may work OK.  (One ran down the
peak of the roof of my apartment building, tucked out of sight under the wood shingles.)
But for a lot of other purposes I tend to use dipoles as my default antenna, or, for multiband
operation, a horizontal loop.  It really depends on my desired coverage area, what supports
are available, and what other options I have.
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