DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
  s=s1024; d=btinternet.com;
  h=DKIM-Signature:X-Yahoo-Newman-Property:X-YMail-OSG:X-Yahoo-SMTP:Received:Message-ID:From:To:References:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE;
  b=uMLJGWkWaPkcgBDJGF1GJ+fRUHol45nwq2P43kACcEma4sC+lpf1Bj5DeN3VOrDSaSHBegAaEiNw2ToBoSiGKxs9ldshnDOpPMGM6hnNldWUzr4gtA7iD7SFqQBEmslJyN+aiRGpC+SsXfiHhY5w/2bxgakoo+r9JEoUgublZmA=  ;
Message-ID: <628FB34D9D1741F2AB02D0ECEB380F01@64683d74b6134b3>
From: "Robert Bennett" <robertgjbennett@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <4FEF4FAB.2010103@iup.uni-heidelberg.de>
Date: Sat, 30 Jun 2012 21:40:58 +0100
MIME-Version: 1.0
Subject: LF: Re: MF dipole
Content-Type: multipart/mixed;
	boundary="----=_NextPart_000_0010_01CD5709.090BE8B0"
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
X-AOL-SCOLL-URL_COUNT: 0  
X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m283.2 ; domain : btinternet.com DKIM : fail  
x-aol-sid: 3039ac1d60564fef64b8730b
X-AOL-IP: 195.171.43.25
X-AOL-SPF: domain : blacksheep.org SPF : none


This is a multi-part message in MIME format.

------=_NextPart_000_0010_01CD5709.090BE8B0
Content-Type: text/plain;
	format=flowed;
	charset="iso-8859-1";
	reply-type=response
Content-Transfer-Encoding: 7bit


 That means, for a MF dipole test i would start to try to lay it 
> on the ground. If this works with reasonable efficiency, so that a QSO 
> is possible, it would be a simple solution for a quick /p MF antenna 
> that can find its place in a back pack!
>

Like K3MT's Grasswire antenna?.

73 Robert
------=_NextPart_000_0010_01CD5709.090BE8B0
Content-Type: text/html;
	name="K3MT's Grasswire antenna.htm"
Content-Transfer-Encoding: quoted-printable
Content-Disposition: attachment;
	filename="K3MT's Grasswire antenna.htm"

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- saved from =
url=3D(0049)http://users.erols.com/k3mt/graswire/graswire.htm -->
<HTML><HEAD><TITLE>K3MT's "Grasswire" antenna</TITLE>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Dwindows-1252">
<META content=3D"MSHTML 6.00.2800.1106" name=3DGENERATOR></HEAD>
<BODY vLink=3D#770000 aLink=3D#0000dd link=3D#000077 bgColor=3D#ddeedd>
<CENTER><A =
href=3D"http://users.erols.com/k3mt/k3mt.html">K3MT</A><BR>presents . .=20
.
<H5></H5>
<P>
<H3>The <I>GRASSWIRE</I><BR>another approach to hidden HF antennas
<P>
<HR width=3D"50%">
</CENTER>
<H5>April, 1997</H5>
<P>
<H3>Deed restrictions got you down? Neighbors intimidating your tower =
plans?=20
Need a really <I>easy</I> portable HF antenna? Then the <I>grasswire</I> =
may be=20
the answer! Virtually invisible, lightweight, and compact (you can carry =
one in=20
your hip pocket), this antenna works! It has been used by K3MT in =
various=20
installations for more than 10 years.
<P>Read on - and listen to the "experts" telling you that this is =
hogwash, that=20
an antenna like this can't work. But it does. And <I>true</I> experts, =
who have=20
taken a decade or more to come to grips with the intricasies of =
Maxwell's Math,=20
know <I>why</I> it works.
<P>This antenna will <I>not</I> out-perform a yagi, or a decent dipole =
up a half=20
wavelength. Not in gain or signal strength, at least. But it will =
survive an ice=20
storm, wind storm, and is practically immune to lightning. And it =
doesn't need a=20
large tower or tall support. I deploy one from my hip pocket at times - =
the=20
balun to match it is larger than the antenna!
<P>
<HR width=3D"50%">

<P>
<CENTER>THE GRASSWIRE - IN BRIEF
<P></CENTER>What is it? Put simply, it is an end-fed, longwire antenna =
that is=20
laid right on the grass. Hence the name. The original grasswire used by =
K3MT in=20
the summer of 1988 was just 204' of #18 AWG magnet wire laid along the =
property=20
line, anywhere from 1" to 6" above the ground. This sketch shows plan =
and=20
elevation views of a typical installation. Both an 8' ground rod and =
optional=20
counterpoise wires are shown. Use one or the other. Both are not needed. =

<P><IMG alt=3D"grasswire plat" src=3D"K3MT's Grasswire =
antenna_files/grass1.gif">
<P>These antennas are largely resistive, with values ranging from 150 to =
500=20
ohms or so on average ground. They have been used successfully on the =
average=20
soils northwest of Washington, DC, on the sandy soils of the Cape =
Canaveral,=20
Florida area, in the rocky, shale soils of the mountains in Somerset =
county, PA,=20
and on river bottomland of Allegheny County, PA. One was used with great =
success=20
by K3MT/VP9 in Southampton, Bermuda - the object of nightly pileups on =
30 m CW=20
for four nights.
<P>
<CENTER>REFLECTION AND THE BREWSTER ANGLE<BR></CENTER>
<P>The skeptic in you will doubt that such low antennas can work. After =
all, its=20
image in the ground radiates and cancels out all radiation. True - if =
the ground=20
is perfect. But nothing is perfect! The grasswire radiates <I>vertically =

polarized</I> off the <I>end</I> of the wire. Extensive monitoring tests =
with=20
wires laid along the great circle route toward WWV, and perpendicular to =
that=20
line, demonstrate the end-fire nature of the antenna. So why does it =
work?=20
<P>When a plane wave reflects from an air-earth boundary, an incoming =
ray=20
reflects, giving an outgoing ray. These two, and the line normal to the =
boundary=20
plane, form a <I>plane of incidence.</I> Solutions of Maxwell's =
equations differ=20
for the case of the E-field being perpendicular to this plane (i.e.,=20
horizontally polarized), and the case when the E-field vector is =
<I>in</I> the=20
plane of incidence. You will probably call the latter "vertical" =
polarization,=20
although this is technically not correct. Electromagneticists (a.k.a =
those who=20
practice Electromagical effects) refer to these cases as <I>normal</I> =
incidence=20
(horizontal polarization) and <I>planar</I> incidence (vertical =
polarization.)
<P>For the normal incidence case, reflection is nearly total, with a =
nearly 180=20
degree phase reversal. Thus very low antennas neither respond to, nor =
generate,=20
appreciable amounts of horizontally polarized radiation. But for the =
planar=20
incidence case, the reflection varies in strength considerably. At some=20
<I>takeoff angle </I>(angle between outgoing ray and the ground) the =
reflection=20
becomes quite weak, and has a 90 degree phase shift. Near this angle, =
the sum of=20
direct and reflected rays will have a magnitude as if the antenna were =
in free=20
space! Of course, at other angles, ground reflection largely cancels the =
direct=20
ray, and the antenna does not radiate well at all.
<P>A <I>reflection coefficient</I> is calculated as the ratio of the =
electric=20
field in the incoming ray to the electric field in the reflected ray. It =
varies=20
from one (total reflection without loss) to zero (no reflection at all.) =
It=20
depends on the takeoff angle, frequency, and the soil parameters =
(dielectric=20
constant and conductivity.) Here are plots of planar incident (vertical=20
polarization) reflection for typical "good" and "poor" soils.
<P><IMG alt=3D"reflection, good soil"=20
src=3D"K3MT's Grasswire antenna_files/good.gif">
<P><IMG alt=3D"reflection, poor soil"=20
src=3D"K3MT's Grasswire antenna_files/poor.gif">
<P>Notice that, at 10 to 25 degrees, the ground reflection is very weak. =
It also=20
is shifted 90 degrees in phase from the incident ray. Therefore, =
radiation from=20
the grasswire, off the ends will be about the same as if the ground were =
not=20
present.
<P>But launching a ray at, say, 15 to 20 degrees takeoff angle, in a =
direction=20
toward Europe, can be useful! That's what a grasswire does. It is lossy =
in all=20
directions, but least lossy when exciting the ionosphere for a long-haul =
DX=20
contact. To demonstrate the point, here's an extract of K3MT's log, for =
October=20
of 1988, (ahh, glory! Yes, the SSN was good then!) using a grasswire: =
<PRE>
Date    GMT     CALL    his/my RST    FREQ    Power

OCTOBER

27      1554   SM6DYK    579 / 559   28004     80
        1601   SM0LBR    569 / 439   21007    100     RAY - STOCKHOLM
        2001   W4JBQ     579 / 569    7029     40     JOE - FT WRIGHT, =
KY
        2141   W8LNJ     579 / 459   28015     80     DAVE - DALLAS, TX
28      0227   W8AO      589 / 569    3547     15     BOB - SILVER LAKE, =
OH
        1720   G3RFE     579 / 559   21016    100     TOM - BARROW
        1932   G0CBW     569 / 559   14029     50     MEL
        1945   VE2FOU    589 / 559    7032    100     ANDRE - IBERVILLE
        2026   KB7UX     569 / 539   21040    100     RUSS - CHINO =
VALLEY, AZ
        2100   I2JIN     589 / 559   14022     40     BOB - COMO
        2123   G3JVC     569 / 559   14022     40     JOHN - LONDON
29      2105   WA200JXT  599 / 599   28015     80     ND

</PRE>Not bad, for a wire on the ground. Notice that contacts were made =
on 80,=20
40, 20, 15, and 10 meters. The signal reports are not fantastic. But =
contacts=20
were made, and ham radio was enjoyed! Five countries were worked in 3 =
days. And=20
the best part of this setup: <I>the neighbors never knew that a ham =
station was=20
on the air!</I>
<P>
<HR width=3D"50%">

<P>
<CENTER>FEEDING THE GRASSWIRE
<P></CENTER>Since this antenna is largely resistive, a simple trifilar =
balun is=20
all that I have ever had to use. This sketch shows how to make a balun =
that=20
works:
<P><IMG alt=3Dbalun src=3D"K3MT's Grasswire antenna_files/grass2.gif">
<P>Typically I pull the insulation off of some indoor telephone wiring =
cable.=20
Four insulated #22 copper wires are inside: discard one of these and use =
the=20
remaining three. Wind about 16 turns on the core, without allowing the =
wire to=20
twist (keep the three conductors parallel at all times.)=20
<P>Notice that this "balun" really matches an unbalanced antenna to an=20
unbalanced transmission line. It is basically a wide-band, three-winding =

autotransformer. Impedance ratios are as shown on the drawing. Generally =
it is=20
necessary to connect the coax to either A2/B1 or B2/C1, and the antenna =
to B2/C1=20
or to C2. This may change from one band to another, and usually does.
<P>
<HR width=3D"50%">

<P>
<CENTER>WINDOM IN THE GRASS
<P></CENTER>
<P>I have elsewhere described a <A=20
href=3D"http://users.erols.com/k3mt/windom/windom.htm">windom =
antenna</A>. While=20
it is usually hung from a pole or in a tree, it works when used in a =
"grasswire"=20
mode. Just lay it on the ground. Dimensions are repeated here for ready=20
reference.
<P><IMG alt=3D"ground-mounted windom"=20
src=3D"K3MT's Grasswire antenna_files/grass3.gif">
<P>When I travel, I take one of these made of #22 insulated hookup wire. =
Since I=20
often set up beside motel parking lots, and often after a day's work, =
the longer=20
wire is black, and the shorter one is red. This helps me determine which =
way to=20
point the windom. Remember, though, that it fires <I>off the long =
end</I>. Of=20
course, it fires the other way, too, but usually works best off the long =
end.
<P>
<HR width=3D"50%">

<P>I hope this has given some of you a good case of curiosity. Go out =
and try=20
one of these ground - mounted wires. They're easy to build. Even the =
balun is=20
easy to build.
<P>If you must, contact us: we can supply a core, a whole balun, or a =
whole=20
grasswire windom setup.
<P>For more unusual antennas, visit my <A=20
href=3D"http://users.erols.com/k3mt/k3mt.html">web page.</A>
<P>And check out my <A=20
href=3D"http://users.erols.com/k3mt/jokalym/index.html">Books</A> for a =
dozen=20
topics about HF antennas.<BR>that includes the grasswire and other =
beverage=20
antennas.=20
<CENTER>73
<P>K3MT
<P></P></CENTER></H3></H3></BODY></HTML>

------=_NextPart_000_0010_01CD5709.090BE8B0--