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Author Topic: Simple indoor HF antenna  (Read 2629 times)
K2BLS
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Posts: 6




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« on: December 29, 2003, 02:40:02 PM »

Hi all,

I am helping a neighbor set up his shack and he wants to install an HF dipole in his attic.  He has a Kenwood TS-570D with autotuner, and would like to operate on 10-80 meters from one, low cost, antenna.  I'm a bit rough around the edges when it comes to that area, using mostly 2 meters, myself.  Does anyone have any info that we could use.  His attic is approx. 40 feet corner to corner and about 8 feet high in the middle.  I'm thinking of an inverted V dipole, bent at the ends.  Like I said, he is on a tight budget and would like something simple and cheap.  Thanks!  73,

Todd
K2BLS
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WB2WIK
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« Reply #1 on: December 29, 2003, 06:55:34 PM »

80-10 meters with a single "low cost" wire antenna that fits into that profile is a pretty tough act.

Sounds like another example of somebody buying a rig before thinking about the antenna...I'd have invested half the cost of the TS570D into antennas and then used the money left over to buy a used rig -- better results, more contacts.  Oh well.

The center-fed wire doublet with bent ends to occupy all existing space isn't a bad idea at all, although using coax to feed it and an autotuner in the rig can become a pretty lossy system, and the autotuner may not find a match at all frequencies, since the antenna won't be resonant in any ham band -- or if it is, it won't be resonant on multiple bands.  Usually when trying to use a single wire doublet on multiple bands, the feedline of choice is balanced line (twin lead, ladder line), to create more tuning options and provide lower loss than mismatched coax can offer.

Problem is, the TS570D has no way to connect to balanced line without using an outboard balun, or possibly an outboard tuner.

Your friend may find that a doublet having strategic traps and multiple elements will work better with a coax feedline, and still provide a shortened, light weight, reasonably low-cost system.  The W9INN shortened dipoles come to mind, like their model MPD-5, which is only 78' long and thus a very shortened 80m dipole that resonates on 80-40-20-15-10 meters.  It sells for $125 plus $7 shipping, not a bad price for what it contains.  It occupies 78 feet of space, but its ends can be bent or wrapped to fit available area.

WB2WIK/6
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K2BLS
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Posts: 6




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« Reply #2 on: December 31, 2003, 09:13:22 PM »

Hello,

Thanks for the quick reply.  He realizes that thinking of an antenna first would have made more sense, but he got an unbelieveable deal on the radio ($450), and had to make a quick decision.  I just wish I would have found it before he did. Smiley

He says likes the idea of the antenna with the trap system... $125 isn't bad at all and within his budget.  Thanks again for your input.

Happy New Year,

73,

Todd
K2BLS
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K2BLS
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« Reply #3 on: December 31, 2003, 09:23:09 PM »

One more thing... Where can we get this antenna?  I tried searching with Google and can't find anything more than a couple reviews, one of which had a link that is no longer there.  Thanks again
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N3ZKP
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Posts: 2008




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« Reply #4 on: January 01, 2004, 11:59:52 AM »

He has a VERY small ad in QST each month. In the January 04 issue it's on page 132.

There's no web site or email address but his phone number is (847) 394-3414  and his mailing address is PO Box 393, Mt. Prospect, IL 60056.

Lon
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WB7DYU
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Posts: 2




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« Reply #5 on: January 06, 2004, 10:38:44 PM »

Todd,
I had a simular problem as your friend.  I had to have an attic antenna due to some restrictions.  I saw an article in a HAM Mag. I'll find it and send the article to you if my description fails.  As the article instructed, I went to the hardware store and purchased a whole box of clothes dryer hose. The type with the metal, spring-like (slinky)construction, with a plastic outside. Don't get the one with the all metal outside.  It's about 4-6 inchs across.  Make sure the slinky part is one piece, take the ohm meter with you to the store.  After getting home I then split it in two, about 256 turns each side if I remember correctly.  I purchased a 4:1, current forcing, balun.  I soldered the metal of the hose to the connections of the balun. The hose slinky part is steel or some type of metal, but with the trend towards cheap theses days you might check to make sure it is. Bring a magnet??  Then I went into the attic, which I had about 35' of room.  I took some 1/4 inch rope with me.  I found one roof brace and tied my best knot.  I strung the rope thru the dryer hose, both sides.  When I got to the other end, I found another roof brace.  I pulled with all I could on the rope and tied it off.  In the center I used a short piece of rope to support the center.  The antenna hangs from the rope, kind of lays on it.  To top it off, connect a metal trash can lid to each end.  This is like a cap. hat??  I just hung them on one of the 2X4 braces up there.  It's a good idea to put a lug on the dryer hose before going into the attic. I removed the lid handle to make it "pretty"?  A 1/4 inch bolt ties it to the "antenna".  My lids are the small ones to allow getting thru the ceiling access.  A short piece of coax goes from the balun thru the ceiling to my tuner and from there to the rig.  I'm in an upstairs closet I made into the shack, so it almost a straight shot down.  I cover 80-10 with no problem.  Seem to talk to whomever I hear.  Yes, it is not the best antenna.  And there are easier ways to go, I'm sure.  It interact with wiring, vents and all kinds of other metal. But, it gets a lot of metal into the attic and keeps me on the air.  Pattern seems to be broadside on 80 & 40.  On 17 & 10 I hear better off the ends.  20 who knows, seems to come from everywhere.  Cost..??  Hose was $12 I think...balun I can't remember, but maybe someone has one laying around....rope, a couple of bucks.  I got my lids free at the hardware store.  But, that's another story and goes along with the phrase "you're doing what?".

If you want a thrill work on attic antennas in Arizona during the summer months. 110 outside and 3 minutes inside.  Best to do work like this in the Spring and Fall.  Also remember to use a mask because it will be dusty, unless you have a finished attic.  Also watch the nails poking down.

I've been a little long winded, but hope this helps. Not my idea, but it works.

John
WB7DYU
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SSBDX
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Posts: 1




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« Reply #6 on: January 09, 2004, 02:38:18 PM »

WB2WIK,

Why don't you get in your car, find K2BLS and beat the crap out of the guy for screwing up so bad as you have arrogantly illustrated.
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M0MCX
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« Reply #7 on: February 04, 2004, 07:20:33 PM »

Todd, a bit late (by 3 weeks or so by the look of it)

My opinion.. there's nothing wrong with buying a nice radio, after all, that's the "user interface", the bit you can play with in the middle of the night, the knobs and dials to enjoy. I have an FT1000MP with a couple of dipoles. I don't see why my antenna should represent a boat anchor.

But readers might like to check out http://www.hamuniverse.com/multidipole.html which I am building. Currently I have a G5RV wrapped around the attic in a "Z shape" configuration together with a separate 20 meter dipole built from mains electrical cable which handles DX very well!

I wonder if this will help?

Callum.
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