[SEDXC] Wire Antennas

Thu Apr 10 07:15:20 EDT 2008

Hal,

I appreciate your input. The figures mentioned came straight from EZNEC 4.
There are based on sound electromagnetic theory. The standard Lazy-H is a
vertical stack of two wires fed in phase. It consists of two one wavelength
wires spaced 1/2 wavelength apart and elevated so that the lower wire is 1/2
wavelength above ground.

You can extend the wire lengths to 1.25 wave lengths and you will have
stacked extended double Zepps. This gives a bit more gain per wire. If the
spacing is increased from 1/2 wavelength to 5/8 wavelength the maximum gain
increases.

In general it is an outstanding bi-directional array for 10 meters, and its
performance holds up down through 20 meters. However, you can press it into
service from 40 meters on down with only fair results.

I'm sure that it will work with the bottom wire 10 feet off of the ground
but in comparison to what? My full size Telrex monobander for 40 is at 110
feet and has 66 foot full-size elements, and screams on the 40 meter band.
If you only have 75 foot trees you certainly would have to put the bottom
wire at 10 feet to get the requisite 66 foot separation of the two
horizontal wires.

Suppose you put a wire just above ground and had the top wire at 66 feet. On
28.5 MHz the take off angle would be 7 degrees. At 7.15 MHz the take off
angle would be 29 degrees! On 40 meters a SINGLE WIRE has a significantly
lower angle than the LAZY-H array. The lower wire raises the angle of the
composite pattern.

73,

John, W4NU

-----Original Message-----
From: Hal Kennedy [mailto:halken at comcast.net] 
Sent: Wednesday, April 09, 2008 8:15 PM
To: John Harden, D.M.D.; 'Robert Carroll'; sedxc at contesting.com
Subject: RE: [SEDXC] Wire Antennas

I hate to disagree - but the bottom wire can be as low as 10 feet off the
ground and a Lazy-H will work fine.  EZNEC confirms this as well as insight
if you really understand how a lazy-H works.

How they work for bottom fed:
A signal arriving from straight above hits the top wire, then the bottom
wire 180 degrees later.  The transmission line connecting the top to bottom
wires, typically open wire line that has a velocity factor of nearly 1 and
is a half wavelength long, delivers the signal from the top wire to the
bottom wire exactly out of phase, and so the antenna pattern has a very deep
null straight up.  The same is true for signals coming up from the ground.
There really are no appreciable signals coming straight up out of the
ground, but the antenna has two nulls - one straight up and the other
straight down - its symmetrical.  Therefore, the antenna tends to ignore the
ground and can be mounted very close to the ground.  When you get below
about 0.1 wavelength (12 feet at 40 meters) the bottom wire will start to
detune due to ground coupling.   For 40 meters a lazy H with the bottom wire
at 10 feet and the top at 76 feet will work great, particularly if the wires
are not dipoles but are EDZs.  Getting to 76 feet can be a problem - the
pines around here top out at about that height.

73
Hal
N4GG

-----Original Message-----
From: sedxc-bounces at contesting.com
[mailto:sedxc-bounces at contesting.com]On Behalf Of John Harden, D.M.D.
Sent: Wednesday, April 09, 2008 8:13 PM
To: 'Robert Carroll'; sedxc at contesting.com
Subject: Re: [SEDXC] Wire Antennas

Bob,

Some typical figures would be:

At 7.15 MHz have the lower wire at about 45 feet. The maximum gain would be
about 6.4 dBi with a take off angle of 33 degrees. The vertical beamwidth
would be 44 degrees, and the horizontal beamwidth would be 99 degrees (-3 dB
half power points).

On 40 meters the pattern is a broad oval with a fairly high take-off angle.
Sufficient radiation occurs at lower angles to make it useable on 40.

See research by L.B. Cebik, W4RNL

73,

John, W4NU

-----Original Message-----
From: Robert Carroll [mailto:w2wg at comcast.net]
Sent: Wednesday, April 09, 2008 7:07 PM
To: 'John Harden, D.M.D.'
Subject: RE: [SEDXC] Wire Antennas

John-

We were considering the Lazy H for N4N Field Day.  We use beams on 20 m up
and wire below that.  High dipoles work decently but we feel the need for a
directional wire antenna on 40m to point to the northwest, aiming for 40m
night time contacts on 40m.  We would be looking for a pretty low angle take
off as Oregon is about one f2 hop away at grazing angle.  Which brings me to
my question.  How high up do the bottom runs of the H have to be above
ground if you want to avoid squirting most of the energy upwards.  If it is
70' or so we could not have trees high enough for the top run.  I have never
used one of these and could get around to modeling one, but if you know the
answer clue me in.  I am suspecting the bottom wire needs to be about a half
wavelength up but I am not sure.

73
Bob W2WG (Bob2)

-----Original Message-----
From: sedxc-bounces at contesting.com [mailto:sedxc-bounces at contesting.com] On
Behalf Of John Harden, D.M.D.
Sent: Wednesday, April 09, 2008 6:20 PM
To: 'Michael Almeter'; SEDXC at contesting.com
Subject: Re: [SEDXC] Wire Antennas

I would go to Home Depot and buy #14 stranded, insulated wire. It comes in
500 foot spools and is quite reasonable. I have built countless wire
antennas over the years, and they are easy to make without buying
prefabricated antennas that are way over-priced.

A great wire antenna for 20, 17, 15, 12 & 10 meters is the Lazy "H". When
configured properly you can see gain figures of 5-6 dBd. You typically feed
this antenna with 450 ohm open-wire line and you will need a tuner. However,
you can work multiple bands with it. It is bi-directional and the specs can
be found in any ARRL antenna book or the Radio Amateur's Handbook, or on the
Internet.

73,

John, W4NU

-----Original Message-----
From: sedxc-bounces at contesting.com [mailto:sedxc-bounces at contesting.com] On
Behalf Of Michael Almeter
Sent: Wednesday, April 09, 2008 5:56 PM
To: SEDXC at contesting.com
Subject: [SEDXC] Wire Antennas

Well,
    Folks, I am looking for a good wire antenna provider. I recently ordered
from Radio Works, 2 "manufacturing defected" antenna's later, I am looking
for a good source of RELIABLE wire antenna's. I built a 80 meter windom,
which has gotten me to 140 countries worked, but am looking for something
that can handle power. Anyone have any suggestions?

Michael Almeter
W4MJA
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