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Author Topic: wire antenna confusion?  (Read 994 times)
KI4QPU
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Posts: 59




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« on: July 20, 2009, 05:58:03 AM »

Ive been looking at info on the web for about two months about different wire antenna (hf)options. I think i'm more confused now than when I started. A similiar question has already been asked, but not exactly the same that I know of and if so I apologize.

With that being said: I have plenty of yard for about anything, as long as it is one wire. I have to keep the wife happy. I can raise it up to about 70',and go out to a full 160 meter length. So far my attention has been on a multiband wire-including G5RV, 160 meter wire and tune up to the rest of the bands, and ocf windom. There is as much information out there as you want to look at on these antennas. I guess what i'm asking for is your observation through "experience" and "comparison" with all or some of these antennas on tx and rx.

I understand at best they are a moderate antenna as compared to a individual resonant cut wire.
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WW5AA
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Posts: 2086




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« Reply #1 on: July 20, 2009, 06:12:30 AM »

You will get 100 answers and 100 antennas. I have never found a better antenna than a good old doublet (see my article "antenna primer"). I have tried all the usual suspects, G5RV, mystery antenna, fan dipole, resonant dipoles (all home brew by the way). The thing to keep in the back of your mind is receiving antennas. Some folks never come to the realization that using the same wire for TX and RX is usually a compromise.

73 de Lindy
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WB5JEO
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Posts: 805




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« Reply #2 on: July 20, 2009, 07:26:40 AM »

After a while, they just start spinning around in your head. That's when you sit back and consider the compromises, which is mostly what antenna design is about, you appear to have few restrictions. Your main restriction is that you get to put up one single-wire antenna. Since size is not (within limits) a problem, I second the suggestion of a doublet cut for 160 and feed with ladder line through a tuner. Multiband wires designed to be fed with coax are compromises to the desire to use coax feed. Sometimes that's a legitimate restriction. But if you can manage the ladder line, there's nothing else that will consistently perform and will be as simple (as well as cheap). You may have to fiddle with the length of the feedline a bit (see discussions of feeding this type of antenna), but that's a very commonly dealt with problem with pretty clear solutions. You've got the very nice ability to get it to 70 feet. Don't worry if you have to erect it in an inverted "V" kind of configuration. It will still work, with probably a more consistent and more circular pattern across the bands. Not that it's all that directional in any configuration.
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AA5TB
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Posts: 81


WWW

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« Reply #3 on: July 20, 2009, 09:13:04 AM »

There are some good ideas already.  Bottom line is to just put something up and don't think about it too hard.  If it doesn't work to your expectations try something else.  You'll learn a lot that way too.  If you analyze it too much it will start to seem like nothing will work.  Some planning is great but it is easy to convince yourself that it isn't worth trying anything.  Some of us dream of having your space.

73,
Steve - AA5TB
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WB5JEO
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Posts: 805




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« Reply #4 on: July 20, 2009, 09:21:01 AM »

Well, that's the truth. After a while, you realize that in the hours you've agonized over the antenna books and articles deciding what wire antenna to build, you could have built three of them, and for cheap, if you're reusing components for the next project.
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AC4RD
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Posts: 1235




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« Reply #5 on: July 20, 2009, 09:21:29 AM »

I'll second (third or fourth, maybe) the suggestion for a simple doublet fed with ladderline.  A lot of hams avoid ladderline, but the antenna WB5JEO suggested will almost certainly work VERY well on every band, it's very inexpensive, and once you learn the trick of getting lines up into trees, it's even pretty easy to put up!  :-)  It's also a great starting place for experimentation, too.  Give it a try!  GL!
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WB2WIK
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Posts: 20612




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« Reply #6 on: July 20, 2009, 09:25:43 AM »

A conventional G5RV is only 102' long and doesn't cover 160m, but does okay on 80-40-20 and will radiate a signal on other bands.

A 160m doublet fed with ladder line all the way to the shack tuner will work great on 160 & 80m and start to be a compromise on the higher bands, irrespective of the ability to match it, because it's just "too long" and develops several narrow lobes mostly aligned along the wire and not broadside to it, as it works on the lower frequency bands.

I don't like antennas that are so "directional" without having the ability to rotate them.

A good compromise wire antenna is a 160m 1/2-wave dipole paralleled with wire dipoles cut for the higher frequency bands and "fanning" down below the longest (160m) wire doublet to provide good spacing between them: That is, a 160m dipole that's a flattop horizontal wire, with, say, a 10m 1/2-wave dipole that's an inverted vee fed from the same point with the wires sloping down about 45 degrees below horizontal on each side; and then dipoles for the "in between" bands also inverted vees, at shallower and shallower slope angles.  Requires two high end supports, and several other somewhat lower end supports, more wire, more ropes: But only one transmission line, and if you use trees to support both ends, the trees won't know you're using them more times.

At least this provides an optimum radiation pattern: Broad, bi-directional and broadside to the wire, for each band.  And it only costs maybe another $20-$30 in wire, ropes and insulators to make it happen.

WB2WIK/6
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NH7O
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Posts: 126


WWW

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« Reply #7 on: July 20, 2009, 11:23:08 AM »

While I use ladder line and a link coupled tuner as others suggest, I agree with WIK that the 160m dipole will be directive on 20m and up, and somewhat less directive on 40m. That may be a fault or a feature depending on who you are trying to contact.

Can you arrange a horizontal loop? (Dear, it's still just a single wire....) A large horizontal loop up high will be much more omnidirectional in practice. They have many small peaks and nulls in the pattern, yes, but in practice they don't seem to be noticeable.

Or just stick with the low bands, with the solar cycle being as it is, 160m and 80m will be the place to be this winter.
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KD8IIC
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Posts: 159




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« Reply #8 on: July 20, 2009, 01:24:04 PM »

If you have an ant. tuner,look up Inverted L or 160m ants. for a small lot.Both grt info. A 100' 12ga stranded & end fed w/your tuner will work great/cheap.NEC compliant too.I'd try to string to insulators to rope to trees.Got gnd.?? 8'copperclad rods. see ARRL Handbook,I even sunk one in the sump pit in basement,can't have too many.bond 'em all together now...Lane 73
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WB6BYU
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Posts: 13342




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« Reply #9 on: July 20, 2009, 01:57:34 PM »

At the basic level there won't be a lot of difference
among the various antennas that have been mentioned (the
G5RV, doublet, OCFD, loop, or multiple half-wave dipoles
with a common feedpoint.)  This presumes that the G5RV is
extended to cover 160m, around 200' long.  All will have
high efficiency (looking at just the antenna itself, not
the feedline yet).  All will have a standard dipole pattern
on the lowest band, breaking into multiple lobes on the
higher bands.  None will have particularly lower angles
of radiation when installed at the same height.

The radiation patterns will vary depending on the exact
length of the wire, the frequency, and how it is fed.  For
example, while all have the same basic pattern on the
lowest frequency where the length is close to a half
wavelength, the patterns on twice the frequency will vary.
With the doublet and the G5RV (which is simply a shorter
doublet) the pattern will still be perpendicular to the
wire but sharper and a bit higher gain.  The OCFD will
have a maximum at about 45 degrees to the wire.  A dipole
will still have a broad dipole pattern even when there are
other antennas on the same feedpoint.  How well any of
these antennas works for you will depend on how well
the radiation lobes are aligned to the direction you
want to talk in.  The late W4RNL had a lot of plots of
antenna radiation patterns on his web site that may be
worthwhile looking through:

www.cebik.com/radio.html

(I think many of them appear in his articles for the
QRP club newsletter, but you'll have to look around and
find them.)


The other difference among the antennas is the input
impedance, and, by extension, the feed method.  All will
show a varying impedance over different bands and will
require a tuner to cover all HF/MF ham frequencies,
though multiple dipoles allow you to adjust the resonant
frequency individually on each band so you can use some
portion of each band without a tuner.  (I have also built
coax-fed loops with a low impedance at some point on
each band, but that is most practical if you want to
work CW on 80m rather than SSB.)

The differences among them, then, become more a function
of what bands the provide a good SWR to the transmitter,
and/or when the feedline losses are significant even if
the feedline can be matched with a tuner.

The G5RV uses a matching section of twinlead to try to
provide a reasonable match to coax on several bands,
though the match is pretty bad on others.  With tube
transmitters one could often get the antenna to load on
all bands, but the SWR is too high for most modern
transmitters.  VK1OD has an excellent analysis of the
losses with various feedline options here:

http://vk1od.net/antenna/G5RV/index.htm

The OCFD feeds the dipole off-center to (hopefully)
make the impedance more constant with frequency.  It can
work on many bands, but again, the resonances come out
best when it is tuned for the low end of 80m.  There are
a number of variations of wire lengths and balun types
that will shift the SWR curves around, but it will still
require a tuner in many parts of most bands.  The balun
operates under less-than-optimal conditions in some
cases, and actual antenna performance will depend on a
large extent to the losses in the feedline and tuner.
The OCFD is also more susceptible to RF on the feedline
because of the unbalanced feed.

The common doublet fed with twinlead or ladder line is
not critical with respect to length, but requires a
wide-range balanced tuner in the shack, which has to be
readjusted with each band change.  Generally the
feedline losses will be lower than for feed systems using
coax cable, but the impedances likely will be outside
the range of most built-in autotuners on many bands.  It's
a good, simple, reliable approach when used with a suitable
tuner.

A loop can be fed with coax (with or without a 4 : 1
balun at the feedpoint) or with parallel conductor
feedline.  The coax feed option requires adjustment of
the wire length to get the resonance positioned properly,
and you might not get all bands lined up at the same
time.  Twinlead or ladder line allows the use of a
tuner in the shack, with similar considerations as for
a doublet.

Multiple dipoles need to be tuned to resonance on each
band to be used, but from then on there is no retuning
required when changing bands.  Feedline losses due to
SWR are low, and operating convenience is high.


So all of them will work, and in a general sense, they
will give roughly equivalent performance, but with a
lot of variations due to the specific installation and
the feedline losses.  One or more of them may have
specific advantages or disadvantages in your specific
situation (for example, a null in the pattern pointing
towards Milan when you string it between two convenient
trees) and some may have high losses on some bands (often
30 or 15m) that may or may not be of interest to you.
Those are tradeoffs that you have to make based on your
own operating preferences.  But none of them are "bad"
antennas, and all will make plenty of contacts.
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N3OX
Member

Posts: 8847


WWW

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« Reply #10 on: July 20, 2009, 07:23:10 PM »

"With that being said: I have plenty of yard for about anything, as long as it is one wire"

See that's your mistake ... the best decisions on what works for you are to pit a couple antennas head to head and see who wins.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K2MK
Member

Posts: 399




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« Reply #11 on: July 21, 2009, 05:06:53 AM »

Regardless of what you decide, your first step should be to install corrosion resistant pulleys at the center if you are figuring on a VEE type of antenna or at the center and ends if the entire antenna will be elevated. The pull cord through the pulley can be the typical 3/16" black dacron antenna cord that everyone sells. Tie the ends of the pull cord together so it can never slip out of the pulley and secure it to the bottom of your tree or other support. Your feet will never have to leave the ground for decades.
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W4MLO
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Posts: 30




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« Reply #12 on: July 26, 2009, 09:52:22 PM »

At Lindy's recommendation I built a 135' 450 ohm ladderline fed doublet. fed it thru a MFJ 993B autotuner. I am SERIOUSLY impressed.

It was my first home built antenna. Beats the hell out of the Carolina 160 Windom I paid $170 for.

W4MLO
Have fun
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K8KAS
Member

Posts: 569




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« Reply #13 on: July 27, 2009, 09:02:51 AM »

Lindy is right on, an open wire fed dipole with a tuner is about impossable to beat for a simple all around antenna. IC comments about DC grounds and still get wiped out, a DC ground is not an RF ground that effects the antenna performance, get over it guys an 8 foot ground rod is nothing when it is expected to effect the antenna performance itself.

My reference is always the 1/2 wave dipole, simple and efficent. All this pattern stuff means nothing when the antenna is below 3/8 wave length high so don't get hooked on the hipe you read in the add's.
A good friend of mine (W8RSS)and I go back and forth on the OCFD/Windom's the G5RV's and it is always give a take on their comparitive performances (real on the air testing), we always go back to a center fed 1/2 wave dipole with tuned feeders 40 or 50 foot high, it is and has proven to be the best ALL AROUND antenna for us. 73 have fun.Denny
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K3MOV
Member

Posts: 504




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« Reply #14 on: August 05, 2009, 03:11:55 AM »

When I was at your stage of my antenna learning curve, I was fortunate enough to find 95 page manual entitled: The Easy Way - HF Antenna Systems by J.M. Haerle.  It certainly cleared up some of the mystery and misinformation for me at the time.  I bought mine from a magazine entitled World Radio which is only published on line now.  I am not sure if they still sell the book.  I checked Amazon with negative results, but when I Googled it I found about the first third of the manual available on the internet at no charge.  You might want check it out.  It certainly clarified some things for me which seem very obvious now.

GL es 73, Tom K3MOV
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