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Author Topic: HF Antennas For Beginners  (Read 2026 times)
KC2MUS
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Posts: 7




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« on: March 15, 2005, 02:57:34 PM »

Please let me apologize for the basic nature of this question:

I want to get the simplest antenna for multi-band HF that will fit in my attic. I have read about dipole, LL, inverted V, etc. but with little but confusion on my end...

Is it possible to build a fan dipole that will work on 24,40,80m bands etc. with a single coax to the HF rig? What lengths? Could I hang it in my attic and start listening?

I have an outbacker attached to the rig now (gift) and I can't hear anything but a local AM station on 1450 that is 1/4 mile away and transmitting megawatts!
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WB2WIK
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« Reply #1 on: March 15, 2005, 03:20:25 PM »

How big is your attic?!?

A fan dipole, or rather a parallel dipole, is a pretty good antenna but one that covers 80 meters needs to be about 130 feet long.  Do you have a 130' long attic?

Even if you let the ends hang down and you zig-zag the wires, an 80 meter indoor dipole is quite a trick, unless you have a mansion; in which case, you'd probably also have a yard so you wouldn't need an attic antenna.

You might want to re-think the 80 meter thing, and just go for parallel dipoles that cover 40 meters "and up" (40 through 10 meters).  Even that will be about 65' long, but if you run it way up by the peak of the attic and let the ends hang down a bit, this will fit in many attics.

If you have stucco siding, aluminum siding or aluminum foil-backed insulation in your attic, an attic antenna is unlikely to work, at least not "well."  But if you have just wood, or vinyl siding, and no foil-lined insulation, an attic antenna can work almost as well as one outside at the same height.

The drawback, though, is a constant: That being, when you have an HF antenna in your attic, that automatically means it's "too close" to other electrical and electronic items in your home, and interference to and from those items is very likely.  This is one of the main advantages of getting the antenna(s) as far away as possible; not only do they often work better "in the clear," but they interfere less.

Your whip antenna isn't likely to hear much unless it's installed on a large and effective ground plane, and even then it's very handicapped.  With HF propagation (conditions) as it has been lately, you'd be best off during the daytime hours trying 17m or 20m, and then switching to 40m after dark -- although 40m can provide lots of daytime contacts, too, they're just more local.  40m after dark opens up and contacts to 3000 miles are very typical, using any sort of dipole that works.

"Tuning" a parallel dipole can be a chore, even when it's in the clear; in an attic, it's a worse chore, because it might mean going up and down a ladder many times.  Still, "tuning" it is worthwhile and will require either an antenna analyzer or an SWR bridge and transmitter.

Good luck!

WB2WIK/6
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KC2MUS
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« Reply #2 on: March 15, 2005, 03:31:56 PM »

Thanks - that's what I was hoping to find out.  Is it easier / faster / cheaper to buy a dipole like that or build it? I am NOT much of an electronics guy (but I stayed at a Holiday Inn Express...)...

Can't hang the antenna at my mansion. They distract from the Rolls Royce collection. You know how it is, I'm sure.  ;-)
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WB2WIK
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« Reply #3 on: March 15, 2005, 03:41:24 PM »

You might look at the Alpha-Delta model DX-CC or DX-EE or whatever they have; these are slightly shortened antennas, factory pre-cut to correct lengths, all you have to do is hang them up and supply coax to feed them.  They work well for their size, and don't cost much.

http://www.alphadeltacom.com

Don't drop the end insulator on the Rolls' bonnet, it can leave a nasty scratch.

WB2WIK/6
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KC2MUS
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« Reply #4 on: March 15, 2005, 03:58:36 PM »

Thanks very much for the help - I'll see if I can get working now!

PS - If you think getting a scratch out of a Rolls is hard, just wait until you scratch the wife's private jet. Wow - some people can't let go of the little things!  ;-)

PPS - good to see that HAM radio hasn't totally lost its sense of humor!
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K9ZF
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« Reply #5 on: March 15, 2005, 04:18:45 PM »

Hang a dipole with as much wire as you can get, feed it with ladder line and use a good tuner...

There are also other stealth antennas worthy of trying.  Loading up flag poles or rain gutters is a good way of getting the signal outside without drawing attention.

73 & GL
Dan

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K9ZF /R no budget Rover ***QRP-l #1269
Check out the Rover Resource Page at:  http://www.qsl.net/n9rla
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K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
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<http://www.qsl.net/n9rla>
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WA6BFH
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« Reply #6 on: March 15, 2005, 04:52:49 PM »

I would like to try this also. I live in a 12 X 12 foot shed. It does have an attic crawl space for storage etc. I was thinking of maybe using an End-loaded dipole, with inductive loads at the tips of the dipole, to bring it into resonance at this fairly low frequency, and limited space.

My question is, how much gain will I get?

Oh, and this should also put the antenna up at reasonable height, about .036 wavelength!

73! John
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N6AJR
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« Reply #7 on: March 15, 2005, 05:05:46 PM »

here is one version..

http://www.hamuniverse.com/multidipole.html

do a google on home brew antennas, multiband wire dipoles, and Fan Dipoles..  all the same,

install it flat top , inverted v or sloper..

some wire, a chunk of coax, and for about $15 or $20 you have a nice multi band antenna and you didi it your self.

starting points is one wire to the center conductor of the coax, one to the shield on the coax, and the other end long enough to reach the radio.

6 meters  54 inches per side

10meters  8'6" per side

15 m  about 12' 9" each siide

20m about 16'6"

40 m 33'

80m 66 '

160 meters about 135 ' per side.

these are all a little long, but just twist them back until resonant, then cut..

the way this works is lets say you have a 5 bander, 10, 15, 20, 40, and 80.

you send an 80 m signal down the coax the 80 meter wires look like 50 ohms or so,and the rf likes it so most of the power goes here,  all the rest are way to short, so they all have impeadeances in the hundreds to thousands of ohms, so very little signal goes there.

also the same if you use a 20 meter signal, most of the signal goes there and the rest are not the right impeadeance so little rf goes there, they are either too long or too short.

you can put them up in a fan arangement, the longest on top and the shorter ones below, held 10 inches or so with spacers ( I like plastic clothes hangers, , you get 1 long and 2 short ones in each hanger but don't let the wife catch you chopping up HER HANGERS) , drill small holes in each end for the wire.

you can also put them in a star ( or umbrella) form with one north-south the next east-west and so on

hope this helps..

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K0RFD
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« Reply #8 on: March 15, 2005, 06:05:51 PM »

It is never faster to buy a dipole, but it might be easier, regardless of whether or not I cast aspersions on your lineage, and in particular your mother.

All kidding aside, a dipole is a doublet 1/4 wave on each side.  What could be simpler than that?  Let alone cheaper, with wire going for $25 or so for a 500 foot spool at your local Home Depot (Lowes counts too, but for maximum impact I only want to menton one vendor)

Seriously.  Build your own dipole.  It's not rocket science.  Start with 468/F just like the question on your license exam.  Then prune for actual fact.

Build your own dipole.  You'll learn stuff that will stay with you for your whole ham "career".  Honest.
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W9OY
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« Reply #9 on: March 15, 2005, 06:57:48 PM »

Why don't you try building a single band coax fed dipole antenna to start?  You can get into multiband antennas after you get a single bander going, and see how well its going to play for you.  I would either try one for 40M or one for 20M.  40M is almost always open to somewhere 24 hours a day so personally I would start there.  If you have a tuner and don't run a lot of power you could even try tuning the thing on other bands.  

73  W9OY
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KC2MUS
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Posts: 7




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« Reply #10 on: March 15, 2005, 08:18:10 PM »

Thanks to all - your advice has been very helpful. I think I'm going to buy a first one, then start building (that way I have a working baseline to play with before getting frustrated)...

Nice to know that everyone is so helpful. Thanks!!!

Now... does anyone know how to get a scratch out of the paint on a private jet?  ;-)
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K5DVW
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« Reply #11 on: March 16, 2005, 04:47:57 AM »

I like the polished aluminum look on my jet. Have you tried that?

Anyway, I just wanted to toss out that if you have ANY electronic stuff in your house like, TV, stereo, surround sound, baby monitors, smoke alarms, CO detectors, or robot wife... you can expect that an attic dipole will cause havoc with one or all of them, especially the robot wife.
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EXWA2SWA
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Posts: 158




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« Reply #12 on: March 17, 2005, 10:53:33 AM »

Being a retread & therefor a newcomer myself, I asked the same questions and settled on an Alpha-Delta DX4020. It's a bit over 40' long (45, I think) and runs about $90.  

As the name says, it works on 40m & 20m. Mine is in the attic, oriented N-S at a little under 20 feet, fed with 50' of RF9914F (Bury-flex - about 25' too long and a little overkill) and a DX Engineering 1:1 balun. SWR is pretty flat all across the lower end of 20m (14060 & under) but a bit spiky on 40m. Remember, there's all that stuff up there: ductwork, cable, telephone, household electricity, etc. thats real close to the antenna.

How well does it work? I operate exclusively CW, at about 100W. Since the end of November, I've worked 47 states (44 confirmed) and about a dozen countries (including Germany) from central Oklahoma.  Not terribly remarkable numbers, but I don't contest and I work DX casually (if I happen across a station, fine, I'll give it a try). I'm more likely to rag-chew with 3 or 4 contacts over a couple of hours than try for a thousand 5-n-n's in a weekend.

Sure, I'd like to work 80m, and 15 and 10, but for minimum investment, easy installation and durable construction, I don't think you can beat this lump of wire.

I believe it's the best single investment I've made.

Best of luck & hope to swap ditties with you soon,
73,
JIm KE5CXX

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W0FM
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« Reply #13 on: March 17, 2005, 11:29:49 AM »

Hi Steve,

I have more than 230 countries confirmed on an Alpha-Delta DX-EE (40-10M) in my attic.  I never use more than 100W. It is easy to install and tune, and around 40 ft long overall.  The ends of mine droop down just a bit to fit the available space.  You can zig-zag the ends to fit too if you prefer.  For under $90 it was an excellent investment.

But, as Ralph pointed out, you'll certainly want to "roll your own" to get the experience you'll need as you learn more about antennas.  You can build your own dipoles and run them at 90 degress from the DX-EE for better, all around, coverage.  

Building is a blast and experimenting even more fun.  But, if you are intent on buying a commercial made antenna, I'd look hard at the DX-EE.

Good luck,

Terry, WØFM
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KC2MUS
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« Reply #14 on: March 17, 2005, 01:49:01 PM »

Thanks - that sounds like a plan. I ended up ordering a DX-CC so I hope to be up and running soon. I am using coax to feed it, so do you think I should add a balun? Whatever that is? ;-)

... and if you put a Balun and a Modem in a room together would they fight?
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