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Author Topic: What Antenna??  (Read 599 times)
N1ZHE
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Posts: 68




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« on: July 19, 2004, 03:48:38 PM »

I live on a small lot. Please see a diagram at http://ftp://www.n1zhe.org . It's in the /pub folder.

I have an Icom 706MKII and a LDG autotuner. As you can see on the diagram, there are powerlines on the right of my lot. The two trees are about 25-30 feet high, but the power lines actually pass through them on the right edge, though my diagram doesn't show this too well.

My house is two storey, the garage is one storey. The roofs of both are steep, not too good for this old man to climb.

My shack is in a room near the trees on the second floor.

Any recommendations for an HF antenna?

Thanks!

David, N1ZHE
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WB2WIK
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Posts: 20595




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« Reply #1 on: July 19, 2004, 04:28:59 PM »

You have a lot of options, there.

First, I must assume the power lines are low voltage (240V) if they are only 30 feet above ground and pass through trees -- that's too low for high tension lines of any sort.  As such, they should be well insulated and considered quite benign with to anything you wish to do.

Still, it would be best to avoid contacting them.

Some recommendations:

A good multi-band HF vertical on a tripod or short roof tower mount on the 2-story house, but down at the "other end" of the house, farthest from the trees, would be good and likely not difficult to install unless the roof is slate or some material not worthy of the load.  If you're timid about climbing a steeply pitched roof, hire a professional to do the installation -- that could be well worth the cost, for your own safety.

A good multi-band HF vertical that is "ground mounted" could also work fine, provided it's installed far enough from the house that the house siding doesn't interfere with its operation.  

You could install a rotary beam antenna on a roof tower, to cover 20 through 10 meters and possibly even six meters as well.  Unless it's a very large beam, it won't be interfered with in its rotation by the trees you show, because you can locate the installation at the opposite end of the house.

You could install any number of wire antennas supported by a variety of things, anywhere on the property where the wires won't directly cross the power lines.  I never have any fear of installing wires several feet above, or several feet below, low-voltage (240V) power lines, as those lines are extremely unlikely to break, and a good antenna installation can be designed such that if the antenna wire breaks, it can't possibly come into contact with the power lines.  Although, frankly, most low voltage lines are so well insulated that if your wire antenna laid directly across them it probably wouldn't make any difference.

Recommend you get hold of a local antenna guru to "Elmer" you through this, possibly lend a hand, or recommend a local professional installer.  Your antenna is the most important part of your station; if you install a good one (or ones), you probably won't need the auto tuner, and can sell that to raise more funds for the antenna(s).

A professional rooftop installation, including drilling and cementing holes, reinforcing the roof if required, and everything else, would never take a professional more than one day to complete.  Probably much less than one day, unless you have some unusual obstacles.

WB2WIK/6
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KC8VWM
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Posts: 3119




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« Reply #2 on: July 19, 2004, 04:44:48 PM »


I saw your diagram.

The End fed longwire or "Zep" gets my vote. They are less complicated to construct than a multi wire- multi band antenna. You will be able to work more bands and they exhibit more gain than a traditional single band dipole.

Here is a photo description of its basic construction.

http://www.nevadaradio.co.uk/acatalog/efw.gif

The way I see it, you have 126 feet of total antenna space to work from. (70ft.+50ft. + Sloped angle will add additional length to the overall space we are working with.)

However, be advised, you did mention powerlines near the trees. however, I am not clear on the proximity or height of these lines. Therefore proceed with this idea with caution.

It would start in the tree at a height of approx. 40 -60 ft.high (if possible)

It would then "slop" down toward the side of the garage and connect to the tope of a 20 foot pole (or mast - stick at top of garage roof - or whatever, be creative) and then "invert" the antena extending it along your 70 foot section of your lot (back yard?) to another pole that is approx 10-20 foot off the ground.

This sloping effect may provide you with some desirable skywave or NVIS propagation characteristics.

Read more about "Zep" or "End Fed" antennas here in my upcoming article on eham:

http://www.eham.net/articles/8829

Another good antenna that will also provide you with lower noise levels and "multiband" coverage at the same time is what is called a double bazooka.

The interesting thing about this antenna design in your particular situation, is that this antenna will help reduce "powerline" noise levels at your station.

Read about it's construction & design here:

http://www.bloomington.in.us/~wh2t/bazooka.html

If a longwire antenna isn't what you expected, then why not try a straight out of the box vertical HF antenna?

73

Charles - KC8VWM
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N6AJR
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Posts: 9908




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« Reply #3 on: July 19, 2004, 05:07:46 PM »

either a hustler 5bvt $159 at HRO or a fan dipole on the bands of your choice


http://www.hamuniverse.com/multidipole.html
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N8NBA
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Posts: 6




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« Reply #4 on: July 19, 2004, 06:16:52 PM »

Just a note, more safety than antenna related.

WB2WIK stated:

"First, I must assume the power lines are low voltage (240V) if they are only 30 feet above ground and pass through trees -- that's too low for high tension lines of any sort. As such, they should be well insulated and considered quite benign with to anything you wish to do.

Still, it would be best to avoid contacting them."


I have worked for a power company as a lineman for the last 14 years. DON'T EVER ASSUME ANYTHING ABOUT POWER LINES!! Some are insulated, some are not. Some higher voltage lines are not as high up as you might think. Just by looking at them you cannot tell the voltage or condition of the insulation unless you are properly trained.

To avoid getting hurt or worse I'd advise staying clear of them.

It could also hit you in the wallet should your antenna fall into the lines and burn them down. Most likely the power company will charge you for the repair.

If you need info about them try calling the customer service office and have the area line garage send a supervisor over to provide you with the correct info.

Just a note...

Bill
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KZ1X
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Posts: 3228




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« Reply #5 on: July 19, 2004, 07:03:08 PM »

David:  I'd like to compliment you on your good job of documenting your question.  You provided key information, in a way that allows people to assist best.  

While the 'net is really an awful place for hams to get help, you have done a lot to overcome the problem of not being there in person.

All this said:  I was going to also offer a suggestion or two, but I don't know what your operating goals or budget are.  Post a note with some guidelines around these 2 areas and that will streamline things a bit.

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WB2WIK
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« Reply #6 on: July 19, 2004, 07:04:31 PM »

N8NBA, I don't disagree with you.

If those were primary lines, however, as opposed to low-voltage secondary, having them run through trees would be pretty exciting, wouldn't it?  The original post made a point to say the lines run directly through the trees.

Still, you're right: It's best not to "assume" anything, and the local utility company will be more than happy to identify the lines for you, and possibly even trim the trees if they're a hazard to safe operation of those lines.

WB2WIK/6
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W8JI
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« Reply #7 on: July 19, 2004, 07:13:28 PM »

Remember three very important things about a Zepp.

1.) If the feedline is not an odd multiple of 1/4 wl long, the feedline can have weird impedances and high radiation

2.) If the antenna is not an exact multiple of 1/2 wl, the feedline can have weird impedances and high radiation


3.) A Zepp requires a very high common mode impedance matching system to prevent RF in the shack. The system may also require a good ground system if the feedline and antenna do not have ideal lengths

Nothing wrong with a Zepp, just be sure you do it correctly. It is a "fussy" system compared to a center fed antenna or a Marconi antenna.


73 Tom
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N1ZHE
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Posts: 68




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« Reply #8 on: July 19, 2004, 11:01:42 PM »

First of all, thanks for all the replies up to now, and for any in the future.

Let me fill in a few blanks.

The power lines by my property and through my trees appear to be of the normal neighborhood variety, but even if they only carried 10 volts, I want to stay clear of them. I have a crude dipole up now that uses the tree nearest the corner of my lot as one of it's anchor points. But I stayed below the lines for the anchor point. I figured if anything fell, it couldn't fall on the power lines this way.

Due to this, the highest point of the present antenna is about 20 feet and the lowest is about 15 feet. The lowest point attaches to the house and the antenna actually touches the house at one point. The siding on my wood frame house is stained cedar shingles.

I can spend up to about $300, give or take a little for an antenna. I would prefer not to put up something as obvious as a beam on the roof.

I also forgot to mention that I bought my house before I decided to become a ham. It is probably in the lowest part of town, in a older neighborhood with small yards (houses close together).

I wouldn't mind a vertical if you think it might work. I have worked a semi-fair amount of DX to USA stations and from this loaction, I have used a dipole cut strictly for 10 meters and worked some worldwide DX with another (cheaper) radio and 25 watts. As I recall, the 10 meter dipole was a lot quieter than my present dipole.

Again, thanks for any help, as well as any future help.

Sincerely,

David, N1ZHE
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WB2WIK
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« Reply #9 on: July 20, 2004, 11:27:58 AM »

If your present dipole is "noisier" than you recall the 10m dipole to be, that doesn't mean much...unless you have them both installed simultaneously and can switch between them quickly.  The bands themselves have been a lot "noisier" lately, with high A and K indexes, compared with, say, six months ago.  Also, if your present dipole is longer than a 10m dipole (you didn't say how long it is), of course it will generally capture more noise -- as well as more signals -- on some frequencies.  Of course, with one end of the dipole being literally in the tree that a power line is passing through, that line may be radiating noise your antenna is capturing, and power lines radiating noise is a huge variable that's usually beyond our control.

A good vertical, in general, will work more DX for you than a good dipole -- all else being equal.  It may not be as much fun in local roundables and such, which is why it always pays to have as many antennas installed as you possibly can.  For example, if your current dipole, compromised as it is, makes contacts for you: I'd leave it there, and install another (or more!) antenna(s) to supplement it.  You might find, as many do, that a vertical is better for DX, but the dipole is better for more local contacts, and there would be a great benefit in having both.

If you don't like your roof and don't have the budget to hire a professional to install antennas up there for you, you might consider a ground-mounted vertical with lots of wire radials.  At least that way, all the work you do is "on the ground," and you can take your time doing it without getting nervous.  And if the radial wires would be in the way, you can (or ask a gardener to) cut small slits in the ground and bury them a little bit (just under the grass is perfect).

Once when my gardener, who arrives weekly to cut and trim, saw me sweating in the summer sun installing a bunch of radials, he volunteered to do it himself, if I'd tell him what needed to be done.  I did, and he did, and he saved me hours of work, for about $20!  A better deal cannot be found this side of Utopia...

73 & good luck!

Steve WB2WIK/6

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W8JI
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« Reply #10 on: July 20, 2004, 07:14:56 PM »

You might just consider a random wire fed against a good ground system. At least that would be nearly invisible and easy to erect.

It really would work quite well, as well as a dipole, if you managed to get a decent ground system. You should locate the tuner at the antenna feedpoint, and then bring coax into the house.

I did this at a city location, and it worked out quite well. The only problem I had was adjusting the tuner. With an auto-tuner...you would be all set.

IMO, this is a great deal more simple and really would work quite well. Maybe it would even let you get the antenna higher.

73 Tom

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KJ7GS
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« Reply #11 on: July 21, 2004, 10:37:47 AM »

I wasn't able to see your diagram, but have you thought about experimenting with half squares or some of the other shortened wire designs?  I used to operate from a second-storey position myself, and used fishing line in a nearby tree as a halyard, and another length of fishing line through a standoff insulator connected at the edge of the roof to bring each corner of a half-square up to "window level".  I connected a short length of coax from radio to antenna corner, and although the antenna was directional, it brought some exciting DX into my life with its low radiation angle!  I cut several half squares for different bands, and since the "halyards" could be used to raise and lower the antennas for complete removal when I was done operating, it became quite stealthy considering the rules I had to operate under.
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