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Author Topic: Which antenna to use???  (Read 632 times)
NU0R
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Posts: 408




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« on: May 20, 2007, 07:06:59 PM »

OK, I have fretted over which antenna to put up to get me on the WARC bands. I have up a tri-bander for 10-15-20 and inverted vees for both 40 and 80. I have the perfect spot left on my small city lot to put up one more wire antenna. I have on hand a shorty G5RV(Iknow, no such thing) but anyway it is 51 ft vs. 102 for the full size. I could use this antenna as one option, hooking the 300 ohm line to coax and into shack(coax under 15 ft in length)---------- As a second option I can build a center fed dipole of 65 ft or so. I don't need another 40 meter antenna so would probably make the length for 30 meters at its lowest frequency.That calculates out to about 46ft or 23 ft. per leg. I have on hand some good quality 300 ohm twin lead. I also have on hand a 4to1 balun by W2DU(not sure call is right), that I could use to make a doublet using 300 ohm twin lead to the balun then into the shack using less than 4 feet of coax. My home brew tuner is not balanced output so can't bring twin lead into shack.---- OK here is my question, which antenna will cover 17, 30 and 12 meters with the best performance. I know that either way is a compromise, but I just want to try these bands and build mono-banders later when I get the feel for it. I can't spend any money right now and need to use the items I have on hand. ---- based on your experience, which antenna will cover those 3 WARC bands. My tuner is built really well with heavy air variable caps and a good roller inductor. I'm sure it could handle 500 watts no problem. Also If I go with the home brew doublet, can you suggest a feedline length to hit near resonance on 30,17, and 12 meters? Again, this is just a test antenna and not etched in stone. I just want to get on those bands for now and plan to build moxons at a later date.  ----Your input is really really appreciated. Tell me what you think!!!    Thanks, Bruce
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AB0RE
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Posts: 293




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« Reply #1 on: May 20, 2007, 07:28:34 PM »

Well, before somebody else beats me to it, I'd better recommend looking into a fan dipole.  In your case it'd just be a dipole with 3 legs on both sides (one for 30M, 17M, and 12M).  A google search should turn up a lot of info on fan dipoles, especially regarding installation (how far the legs have to be apart) and tuning (i.e. is it best to tune lowest or highest bands first).

This would probably be the cheapest route and, as an added bonus, you'd be able to use the three bands without a tuner.  Especially 12 & 17M at least as they are small bands and your antenna should be relatively broadbanded at those frequencies.

73,
Dan / ab0re
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N3OX
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« Reply #2 on: May 20, 2007, 07:30:00 PM »

Bruce,

I think you should stop fretting and put something up.

Do you have an antenna analyzer?  You could try some lengths of flat-top and twinlead and see if you can hit close to 30,17 and 12 that way.  

Someone else could design it for you too; I'd point you to a link if I knew of one but I can't find one now... but you could work it out experimentally...

If you don't have an antenna analyzer but do have an SWR meter, a fan dipole might be a good choice.

There could certainly be an optimum solution but someone would have to work one out either experimentally or theoretically and it would take time either way.

So why not stick up 65 feet of wire fed with twinlead and fiddle with both till you get somewhere near resonance on 30, 17, and 12?  You can always fall back on running that twinlead into the balun and a **very short** run of coax to the tuner and that will work reasonably well no matter what.

73,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N3OX
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« Reply #3 on: May 20, 2007, 07:38:59 PM »

Oh, Bruce... just in case he doesn't pop in here check this out:

http://www.w5dxp.com/notuner.htm

Cecil, W5DXP, has worked out the feedline lengths to match a 66 foot dipole on all the bands above 40m... check out the "shorty" down a bit on the page.

Not sure if it works right with 300 ohm line, but this will give you a starting point, perhaps.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N6AJR
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Posts: 9908




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« Reply #4 on: May 20, 2007, 07:41:01 PM »

http://www.ku4ay.net/dipole.html
http://www.qsl.net/kd7rem/antdipole.htm
http://www.hamuniverse.com/multidipole.html
http://www.angelfire.com/nb/ni4l/ni4ldipole.html
http://www.arrl.org/tis/info/pdf/9611073.pdf
http://www.geocities.com/n2uhc/2banddipole.html
http://www.qsl.net/na4it/fandipole.html
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K4JC
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Posts: 76




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« Reply #5 on: May 20, 2007, 08:09:37 PM »

You might also want to check out one of the "off-center fed" dipoles such as Buckmaster or Alpha Delta offer. You can also easily build your own with a 6:1 balun. Lots of good info on either of the above-mentioned manufacturers' websites.
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N6AJR
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Posts: 9908




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« Reply #6 on: May 20, 2007, 08:53:43 PM »

really if you get to where you can spend some $$$ for a superb antenna look at the steppir 6-80 vert. a perfect match on all bands, and nice folks to boot.
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AC5E
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Posts: 3585




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« Reply #7 on: May 21, 2007, 04:07:26 AM »

Since Katrina took down my antenna supports I'm down to an Alpha Delta DX-CC at 20 feet - and a Cubex 4L at 70.

The DX-CC is a cloud burner on 80 but it will fit in just over 80 feet, less if you bend it, it works quite well on 40 and fairly well on the WARC bands, and it is built like a tank. It easily handles legal limit from the Alpha without giving me aggravations. Other than turning the knobs on the antenna tuner once per major QSY.

Over the years I have tried just about everything that has come out. You get what you pay for, there is no magic about antennas, and many of the people selling antennas probably have good intentions but poor judgement.

73  Pete Allen  AC5E

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W7AIT
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Posts: 489




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« Reply #8 on: May 21, 2007, 08:07:52 AM »

BW-65.  Works well.  Mine only 30 feet at apex.

Broad band 4-30 mhz, less than 2:1 SWR over the entire range.

Have patterns if you're interested.  Works ton of DX.

Antenna quiet also, gets common mode noise cancelling as is folded dipole design.

I am pleased with this antenna's performance.  I had a BW-40 and that worked well too.
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WW5AA
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Posts: 2086




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« Reply #9 on: May 21, 2007, 08:43:07 AM »

I would just feed the 40 meter dipole with 450 ohm ladder line, a coax balun to the tuner. That will work better than anything you can buy.

73, de Lindy

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