Feeding the Halfwave Ant

[n0tu/Steve]

This may be silly question? I'm trying to cut down on set up time and
weight for my backpacking journeys into the field with QRP gear. The
end fed halfwave or random wire 'sounds' good to me becasue of the no
feed line and a simple LC tuner can be used. Opposed to CF halfwave
with balanced tuner (heavy toriod) and additional feedline weight?

OK heres the REAL question: once you have a halfwave, (5/8 or 3/4 wave
whatever) suspended in the tree or on a pole, Does it really matter
how it gets fed? Wouldn't end feeding give the same result (or
should?) as center or even offset feeding? Of course this assume a
it's over a pefect ground etc (But truth is I'm usually over very poor
ground situation)

It seems to me the endfed half-wave inverted vee should give me the
same result as the center fed inverted vee and have the benefit of
leaving the feedline at home. But may limit where I park my tent and
how the antenna gets supported etc? Am I missing something -- w/my
limited knowledge of antennas?

My experience has been the CF antennas have out performed (or so I
think) than my end fed setups? But I may not have properly match the
EF ants or I may be CF-biased from what I've read? Where's the TRUTH??

Steve/n0tu
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[Leon Heller]

----- Original Message -----
From: "n0tu/Steve" <[hidden email]>
To: "qrp-l" <[hidden email]>; "ElecraftLIST"
<[hidden email]>
Sent: Tuesday, June 13, 2006 2:21 PM
Subject: [QRP-L] Feeding the Halfwave Ant

> This may be silly question? I'm trying to cut down on set up time and
> weight for my backpacking journeys into the field with QRP gear. The
> end fed halfwave or random wire 'sounds' good to me becasue of the no
> feed line and a simple LC tuner can be used. Opposed to CF halfwave
> with balanced tuner (heavy toriod) and additional feedline weight?
>
> OK heres the REAL question: once you have a halfwave, (5/8 or 3/4 wave
> whatever) suspended in the tree or on a pole, Does it really matter
> how it gets fed? Wouldn't end feeding give the same result (or
> should?) as center or even offset feeding? Of course this assume a
> it's over a pefect ground etc (But truth is I'm usually over very poor
> ground situation)
>
> It seems to me the endfed half-wave inverted vee should give me the
> same result as the center fed inverted vee and have the benefit of
> leaving the feedline at home. But may limit where I park my tent and
> how the antenna gets supported etc? Am I missing something -- w/my
> limited knowledge of antennas?
>
> My experience has been the CF antennas have out performed (or so I
> think) than my end fed setups? But I may not have properly match the
> EF ants or I may be CF-biased from what I've read? Where's the TRUTH??

The classic end-fed half-wave antenna has a 1/4 wavelength counterpoise.
Here is a useful description which mentions some of your variations:

http://www.njqrp.org/n2cxantennas/halfer/index.html

73, Leon

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[Peter Zenker]

 Steve,

IMO you will find more center feed halfewave antennas then endfeed halwaves
because at Home it is normaly not so easy to have the ATU directly to the
antenna without feeder line. Endfeed halfwaves with feeder line result in
high impedance coupling which is not so easy to handle.

If we talk about portable Antennas, here in Germany the endfeed halfwave,
coupled directly to the ATU has become  one of the most used portable wire
antennas ever. It´s efficiency is great even if it ends very near to ground
with it´s feeded side. We use what we call a "Fuchs Kreis" to tune it. (this
type of Antenna was described By Mr. Arwed Fuchs, an Austrian Radio Amateur
in 1928. The Fuchs Kreis actually is a halve wave parallel tuned Circuit,
the antenna is directly coupled to the High impedans top of it. To make it
multiband, we use 2 Torroids with tapped coils, a switcheable coupling
winding and  a variable capacitor (exactly the same as it is used in the ZM)
BTW, the Z-Match itself is also a tuned parallel circuit. The difference: it
uses a different coupling method and it tunes to frequencies the same time.

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If you are interested, you will find the complete manual of our Multband
Fuchs here: http://www.qrpproject.de/UK/fuchs_ant_.htm

It is great for backpacking because it is very small, it needs no feeder, it
needs no counterpoise and it gives a ton of preselection to your receiver as
well.

73 de Peter, DL2FI

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[Don Wilhelm-3]

Steve,

If your tuner is of the L network type (like the Elecraft auto-tuners), it
will have a difficult time matching the high impedance of a half wave end
fed antenna.  If you want something similar, use the W3EDP length antenna -
an 85 ft. radiating section with a 17 ft. counterpoise wire in place of the
half wave.

If you insist on feeding a half wave antenna at the end, plan to use a
parallel tuned circuit to tune it - the Z-match tuner is a multiband tuner
of that type and will tune high impedances fine.

I personally consider the center fed configuration to be less troublesome
because it is inherently balanced, but then you have to set it up in a
balanced configuration to preserve that balance, and I usually end up with
an inverted VEE configuration which works just fine with one support.

73,
Don W3FPR

> -----Original Message-----
>
> This may be silly question? I'm trying to cut down on set up time and
> weight for my backpacking journeys into the field with QRP gear. The
> end fed halfwave or random wire 'sounds' good to me becasue of the no
> feed line and a simple LC tuner can be used. Opposed to CF halfwave
> with balanced tuner (heavy toriod) and additional feedline weight?
>
> OK heres the REAL question: once you have a halfwave, (5/8 or 3/4 wave
> whatever) suspended in the tree or on a pole, Does it really matter
> how it gets fed? Wouldn't end feeding give the same result (or
> should?) as center or even offset feeding? Of course this assume a
> it's over a pefect ground etc (But truth is I'm usually over very poor
> ground situation)
>
> It seems to me the endfed half-wave inverted vee should give me the
> same result as the center fed inverted vee and have the benefit of
> leaving the feedline at home. But may limit where I park my tent and
> how the antenna gets supported etc? Am I missing something -- w/my
> limited knowledge of antennas?
>
> My experience has been the CF antennas have out performed (or so I
> think) than my end fed setups? But I may not have properly match the
> EF ants or I may be CF-biased from what I've read? Where's the TRUTH??
>
> Steve/n0tu
>

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[Ed - K9EW]

Hi Steve,

As long as you mentioned the inverted vee, I thought I'd offer this to think
about.  I have been using a 20m center-fed inverted vee with very good
results.  And here's the great thing about it... it's a coil of TV
twinlead.  One end of the twinlead is split to form the two arms of the vee
(each approximately 17 feet long), and then the remainder of the twinlead
becomes the feedline which you can connect directly to your rig.  The only
constraint is that the feedline portion of the twinlead *must be* an
electrical half-wavelength long (about 29 feet, depending on the velocity
factor of the twinlead you use) in order to present a 72 ohm impedance to
your rig.  It's small (rolled up), lightweight, and requires one branch
about 30 feet off the ground for the vertex.  At this height, it's
approaching a half-wavelength above the ground which is great for
the radiation pattern.  The ends are tied off with small ropes to stakes (or
rocks) 30 feet from where the feedline would touch the ground.  This will
give you a 90 degree angle at the vertex.  It's balanced, so no
counterpoise.  And it works just like a "home" antenna.

72/73,
ed - k9ew


On 6/13/06, n0tu/Steve <[hidden email]> wrote:
>
> It seems to me the endfed half-wave inverted vee should give me the
> same result as the center fed inverted vee and have the benefit of
> leaving the feedline at home.
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[Stuart Rohre]

My 49 years of antenna useage has taught me it is bad to bring the high
voltage end of the antenna down close to the earth because of ground losses
due to the capacity of the antenna to earth.  Not to mention the high RF
voltage induced into the shack.

My center fed antennas have all worked much better than my end fed antennas,
all the way from end fed quarter wave to a 400 foot long end fed long wire.
Those two were the worst, and were possibly aggravated by being used over
very poor earth as to RF conductivity.

If you could keep the end of an end fed antenna up high, or put the LC
network up at the end of a high wire, and run coax to the rig, you could
avoid the bad effects of bringing the fed point "into the shack".

You could also end feed the wire with balanced line in the Zepp feed
arrangement.  Current unbalance there is only 10 per cent per L. B. Cebik's
modeling. (W4RNL's antenna site www.cebik.com)

For a field portable center fed half wave horizontal, you do not absolutely
have to use a balanced tuner, or even a heavy balun!   You can use a one to
one cable bead choke on the end of an L net tuner.  Minimal inductor loss,
(only one), and one C.  Use of correct length of feeder with such a tuner,
brings the impedance within range of the tuner.  Or use the bead choke on
the output of a conventional Tee tuner.

Stuart
K5KVH


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