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Author Topic: Apartment dipole  (Read 427 times)
WA7UHR
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Posts: 8




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« on: December 19, 2006, 02:09:03 PM »

Due to antenna restrictions, I am contemplating a dipole for 75/80 meters in my apartment.  I am wondering if I could run wires of the correct length at the intersections of the wall/ceiling.  Many right angle bends and perhaps some overlaping will be necessary.  Would a dipole of the correct length with all these right angle bends (etc) work with my 756 Pro II/antenna tuner?   Thanks in advance, Fred wa7uhr since 1971.  PS I love ham radio!!
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AA8LL
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« Reply #1 on: December 19, 2006, 02:21:32 PM »

You may need a bit longer than the "correct" length dipole but some length will work with your built-in tuner.  Be prepared for poor performance and rfi into phones and intercoms and fire alarms throughout the apartment building.

73,
Wade
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WA7UHR
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« Reply #2 on: December 19, 2006, 02:39:54 PM »

Thanks Wade, Merry Christmas.  de Fred...
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N6AJR
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Posts: 9910




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« Reply #3 on: December 19, 2006, 03:30:43 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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KZ1X
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Posts: 3228




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« Reply #4 on: December 19, 2006, 04:54:09 PM »

for such a low frequency in such a confined situation, you'd be WAAAY better off with a magnetic loop ...

http://www.iw5edi.com/ham-radio/11/a-magnetic-loop-antenna-for-hf

MANY dozens of websites on the subject ...

you could make one better than that described, but, probably not easier
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K0ZN
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Posts: 1553




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« Reply #5 on: December 19, 2006, 08:26:54 PM »


Hi.

Yes, you can make it "work" (i.e. radiate) but I would suspect LOTS of interaction/coupling, etc. with the AC power wiring, water pipes, heating/cooling ducts and other steel in the building which will make it very difficult to get a "normal" resonance on a dipole. I suspect you would have a real challenge trying to trim it to length due to the coupling to other objects and it may likely have high SWR, even at resonance. There is no guarantee of this problem, but the odds favor it.

It would seem that the best way around this is to forget trying to tune it to resonance and just use a decent commercial Antenna Tuner with a balanced
output (typically, via a balun). Your line run would be so short that line loss is inconsequential. If you limit the power to 100 watts or less, a good quality (i.e. largest wire gauge) 300 ohm TV twin lead should work fine in your application. You could also use 450 ladder line, or coax and a balun designed for high SWR service (a basic 1:1 baluns WON'T like this application... you need one of the baluns specifically designed for this kind of use.) Personally, I would try the 300 ohm TV line first. Just don't forget there will be some decent voltage on the transmission line and keep it away from metal, etc.

What is the construction of your building? Some commercial buildings use steel "studs" in the walls....those could be an issue, especially on the higher bands; if you have wood studs/construction you will be much better off. The earlier post that cautioned you about RFI...possibly to neighbors is valid. It would behoove you to keep your power in the 25 to 40 watt range until you get a feeling for any RFI problems. (Personally, I would NOT tell anyone I was operating a radio transmitter... you are just INVITING complaints and problems!!)

One other alternative would be to make a "Slinky" type coil antenna, that is some form of spiral wound "loaded" antenna. This could be a combination. You could have part of the antenna straight wire and wind a loading section on something like 1" dia. PVC pipe.

Have you considered some kind of outdoor "Stealth" antenna?...or is that out of the question?

Pick up a used copy of the ARRL Antenna Book... you likely will get some idea/thoughts out of that, too.

Bottomline: You CAN get on the air and a good Antenna Tuner would be a Major asset in your installation and likely reduce antenna tuning problems a ton.

Good luck!   73,  K0ZN
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KB9CRY
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« Reply #6 on: December 19, 2006, 08:39:55 PM »

Other Bottom-line is:  HF antennas should be outdoors.
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KC8VWM
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« Reply #7 on: December 20, 2006, 05:49:17 AM »

Stealth antenna's are the way to go.

You can disguise many outdoor objects as antennas. The feedline leading to a dummy satellite dish can be used as a longwire antenna for example.

A patio umbrella can be taken apart and reassembled and disguised as an outdoor loop antenna.

A crappie pole can be propped up against a wall outside with a fishing tackle box beside it and used as an outdoor antenna.

73 Charles - KC8VWM





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KB4QAA
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Posts: 2407




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« Reply #8 on: December 20, 2006, 08:16:42 AM »

It may be tough to set up a resonant dipole but give it a try.

I live in a townhouse, and used copper foil around the base board of one floor as the counterpoise and a section of a vertical run up the stairwell for the radiating element.  This setup is analogous to sailboat arrangements.  Gordon West has a series of articles that discuss this.  

25 watts is about the most I can run without RFI.  I found SSB impractical, but was able to easily work PSK31 until the has from switching power supplies, flat screens and plasma displays in my complex became overwhelming a couple years ago.   Power isn't everything and 25 watts is only a few db down from 100watts.

"If an antenna is silly but works, it isn't silly".  Good luck.  bill.
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N3OX
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« Reply #9 on: December 21, 2006, 06:24:57 AM »

"Other Bottom-line is: HF antennas should be outdoors."

I agree.  I'd go to extremes to get an outdoor invisible antenna up before I settled for an indoor one, especially on 75/80.

I operated from an apartment for a couple of years and had good luck with outdoor magnet wires into a couple of trees near my apartment.

I started with a copper tape stuck on my balcony wall and ceiling (nonconductive) fed against the railing.  Much better than that was a random wire into a tree fed against the railing.  Another big improvement was seen when I got another magnet wire into another tree and fed the two as a doublet with a tuner on the balcony:

http://www.n3ox.net/projects/servo

The signal to noise ratio on the doublet with a good choke balun on the tuner output was much, much better than the signal-to-noise on the wires that used the railing as half of the antenna.  In fact, grounding the tuner to the railing increased the noise by 2 s-units on most bands and more on some.  I even saw a difference in the noise by moving one of the doublet wires so it was a foot away from the building rather than 2 inches.

The moral is that an apartment building is just hot with RF junk.  The less interaction between your antenna and an apartment building, the better.

If it's really, truly impossible to put up outdoor antennas, then indoor is better than nothing.

However, magnet wire is more or less invisible.  Find the wire crossing this picture:

http://www.n3ox.net/projects/antennas/VHFcontest1_lg.jpg

As you can see from the VHF antennas, I was able to get away with a lot more than one might think at an apartment building.  The VHF antennas were temporary; I only put them out when I was using them.

The HF wire was up 24/7.  I had to look for it pretty hard to see it... and don't think anyone else saw it.

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

Monkey/silicon cyborg, beeping at rocks since 1995.
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