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Author Topic: Antenna set up help  (Read 1788 times)
KF7ZCH
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Posts: 13




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« on: January 03, 2013, 06:58:10 PM »

I am a new general class operator.  I have gotten a new hf radio and I want to put up an antenna.  On my roof a loop antenna would be preferable.  I want to consult anyone on eham.nets forums to help me.  My proposed idea is as follows:  I want to make an 80 M loop.  I want feed it with ladder line or something similar, have a balun and have coax to my antenna tuner then to my radio.  I would like to know if this is a decent setup or if the effort, at least on my roof, to get a dipole up is worth the effort.  Can my setup produce low swr and get a fair amount of my rig's 100 watts to the antenna?  If this antenna system works, what kind of balun would I use.  Responses are greatly appreciated.  I am open to people's ideas and responses. Thank you.

KF7ZCH
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WB6BYU
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« Reply #1 on: January 03, 2013, 07:03:11 PM »

How big is your roof?

An 80m full-wave loop is about 270' of wire (depending what part of the band
you cut it for.)  That's going to be around 70' square.  I've strung such a loop
around my back yard, but I've never lived in a single family home that was
big enough for one.  A 40m loop, which is half that size, will fit in many cases.

If you have room for such an antenna, it is a good place to start.  Performance
will depend on height above ground, as with most types of antennas.  (While
a 2-story house improves the antenna height, it also reduces the area of the
roof to install the antenna.  At least for us mere mortals who can't afford
a mansion.)
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KF7ZCH
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« Reply #2 on: January 03, 2013, 09:07:03 PM »

Thank you for the help.  I had miscalculated my length of my loop and my roof may be more suitable for 40 altough I could stretch it and see if I get 40M. And If I have a mansion house, I wonder what kind of backyard you have!
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VA7CPC
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« Reply #3 on: January 03, 2013, 09:28:09 PM »

If you run ladder-line to the antenna, you won't have to worry about feedline losses.  The SWR has to be _very_ high before they become important.

That was the logic behind the (very old) Johnson "Matchbox" balanced-line tuners.  They would (or so I've heard) match over a very wide range, and I think they were inductively-coupled, so the output was truly balanced.  They are occasionally available on eBay and at hamfests.  I passed one up a few years ago -- couldn't justify the closet space to store it.

I suspect that, with a 40m loop, you could probably operate on 80m with such a setup.

.            Charles
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WB6BYU
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« Reply #4 on: January 03, 2013, 09:31:50 PM »

Actually, at the moment I live on 3 acres out in the country, and I've put up
full-wave loops for 160m.

But the one in question was in a suburban house, on less than a quarter of an
acre.  It went from one corner of the roof over to a post on the fence, back
to another post, across to the apple tree, another post on the fence, up to the
top of my antenna mast, down to a corner of the roof, over to the chimney, out to
the end of the garage roof, and back to the starting point, from which the feedline
ran into the attic through a screened vent, across the rafters, then dropped down
through a hole in the ceiling to a tuner sitting on top of the radio.

Since an acre is 1 chain by 10 chains, and a chain is 66', it only requires about
1/10th of an acre to put up an 80m full wave loop, though one doesn't always
have the option to run it right around the edge of the property.


I would suggest starting with a 40m loop to see how it works.  Then you can
plan how to squeeze in an 80m loop later if you want to.
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WA3SKN
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« Reply #5 on: January 04, 2013, 05:06:45 AM »

Depends on your definition of "decent".  You should be able to load and make contacts.
I would be more concerned about noise pickup from the local sources in the house that can be a problem.  Getting the antenna away and in the clear can lower those local noises and make it more enjoyable from the listening standpoint!  This all depands on the house layout, area available, and of course... where the power lines are.
Loops are great, but having a house in the center of them is not!
73s.

-Mike.
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KF7ZCH
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« Reply #6 on: January 04, 2013, 06:44:04 AM »

Depends on your definition of "decent".  You should be able to load and make contacts.
I would be more concerned about noise pickup from the local sources in the house that can be a problem.  Getting the antenna away and in the clear can lower those local noises and make it more enjoyable from the listening standpoint!  This all depands on the house layout, area available, and of course... where the power lines are.
Loops are great, but having a house in the center of them is not!
73s.

-Mike.

In response to your post I have a question.  I am hoping to have the loop on my roof.  Will that help in removing the ambient noise of the antenna?  In additon, the powerlines in my neighborhood are underground.
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WB2WIK
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« Reply #7 on: January 04, 2013, 08:58:17 AM »



Quote
In response to your post I have a question.  I am hoping to have the loop on my roof.  Will that help in removing the ambient noise of the antenna?  In additon, the powerlines in my neighborhood are underground.

What is "on my roof?"  Laying on the roof, or under the eaves, or insulated and inches or feet above the roof?  Or what?

Usually, for best noise immunity, you wouldn't want an HF antenna on or near the house at all -- because a lot of noise we hear on the HF bands comes from the electronic products operating within the house.  Thus, the closer you are to those products, the more likely you are to near noise generated by them; similarly, the close you are to those products, the more likely your transmissions are to interfere with their normal operation.

It's almost always best to keep antennas as far away from the house as possible.
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K8AXW
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« Reply #8 on: January 04, 2013, 09:51:00 AM »

ZCH:  I mean no offense, please believe me.  With that said, I must ask, why in the world would you want to complicate your life like this?  With all the antenna designs available, why would you want to get involved with a loop antenna; mounting it on your roof with open wire feeders, baluns, etc? 

To my way of thinking, a new General wanting to get on the air and make contacts (which is one of the main reasons for becoming a ham) the simplest antenna that I could fit in my yard is the way to go.  THEN, and only then, would I even consider something as ambitious as what you want to do.

Antenna experimentation is another great facet of ham radio but it's usually done by someone with a great deal of knowledge about antennas in general.  Not someone starting out.

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WB6BYU
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« Reply #9 on: January 04, 2013, 10:37:34 AM »

A loop antenna run around under the eaves or tucked under the shingles isn't the
ideal antenna - it is affected by the building, and will pick up electrical noise from
many sources inside.  But sometimes that is the best you can do, and it can work
reasonably well when you can't put up something bigger and/or higher in the air.
It does have the advantage that it can be totally invisible from the street.

When total invisibility is not a requirement, you may be better served by
putting up a mast (5' to 20', whatever you can manage) in the middle of your
roof and using it to support an inverted vee dipole for multiple bands.  You can
feed it directly with coax and add as many bands as you want, one or two at
a time as you find what best suites your operating style and preferences.  That
gives you a good match, you get the experience of tuning antennas, they are
easy to do, and you don't have to worry about an antenna tuner.  The added
height of the mast will improve performance on the higher bands, and you have
more separation from noise sources in the house (even if it is just a few feet.)
You can even experiment with a shortened 80m element at some point.

The dipoles will probably work at least as well as the loop, especially if they
are up higher off the roof.  (At the same height,  the loop will be better
in some directions and worse in others, especially on 15m and 10m.)

This approach requires that you get up on the roof to tune the antennas to
resonance:  sometimes that isn't convenient or safe.  If that doesn't work for
you, there are other options.
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N6AJR
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« Reply #10 on: January 05, 2013, 03:22:41 PM »

fan dipole.
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N3DT
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« Reply #11 on: January 05, 2013, 06:57:57 PM »

Look up C-Pole antenna.  All it requires is one support.  No radials, needs a current balun which is easy to make.  Coax fed.  Vertically polarized so it may pick up some noise, but a 40 M one is relatively easy to get up.  80M requires some 50-60', 40M half that.  Plus it works on most bands above the cut band.  I have one for 80 and one for 60 and they work on every band I want, 160-6.   I hang them from trees in the yard, and they are nearly invisible if you use black wire and paint the spreaders flat black.  I have a bunch of 600 ohm coated telephone wire, plastic coated copper coated steel wire.  They work great for me.  All you need is some wire, coax, some PVC pipe and a balun which can be bought as a kit for about $20.  If you're close by, you can have my 40M one which I don't use.
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K8POS
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« Reply #12 on: January 06, 2013, 09:24:47 AM »

Since you said you were new to HF, I would recommend to first put up a G5RV type antenna.
No I am not a supporter of them, but it will do two things for you.
1) Get you on the air on most of the bands with a tuner at minimal cost.
2) Let you decide what band or bands you like best.
From there you can decide what type/style antenna best suits you needs, and go from there.
I run a full size 80 meter loop, for me it gives the best multi band performance, but suffers from not being the best as separate antennas for each band would be.
A 40 meter loop around the roof of you house WILL WORK just not as well as the same antenna 30' in the air over open ground.

Bob
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AC2EU
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« Reply #13 on: January 06, 2013, 12:03:37 PM »

Since you said you were new to HF, I would recommend to first put up a G5RV type antenna.
No I am not a supporter of them, but it will do two things for you.
Bob

A G5RV? If you are going there, why not tune a random wire? It's just as good and does not have all of the folklore attached.  Grin
A dummy load would be my second choice  Roll Eyes

When I was new at hamming, a couple of veteran hams suggested a G5RV . Fortunately I researched it before I just took their word for it... I would have been pissed.

Yes there are people who do QSOs on the G5RV, but remember, it is possible to make contacts at QRP levels, which is what you may have on some bands with 100W input!!! Go green, get a a reasonably resonant antenna!
Basic Dipoles are nothing but some properly cut wire, rope and three insulators. No reason not to make one!
A 20M dipole is around 33 feet long and 20M is a great band...
« Last Edit: January 06, 2013, 12:17:41 PM by AC2EU » Logged

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