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Author Topic: 10 meter dipole in apartment  (Read 4660 times)
NU9J
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« on: June 05, 2011, 06:51:58 AM »

I have the space in my apartment for a 10 meter dipole, either mounted against the wall or laid out on the floor. I am about 18 feet above the ground, so about 1/2 wavelength. Does anyone have any similar experience? I want to know how effective such an antenna can be in my situation. Thanks.
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~Philip
N3OX
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« Reply #1 on: June 05, 2011, 07:53:06 AM »

I have the space in my apartment for a 10 meter dipole, either mounted against the wall or laid out on the floor. I am about 18 feet above the ground, so about 1/2 wavelength. Does anyone have any similar experience? I want to know how effective such an antenna can be in my situation. Thanks.

No way to predict; you'll just have to try it.

Some apartments (lots of reinforced concrete) are going to be opaque to RF or nearly so.  Others (wood and vinyl siding, townhouse type places) will be better, but performance will be a complicated function of wiring, plumbing and ductwork.

Indoor antennas will tend to be vastly more noisy than ones that aren't quite as tightly coupled to wiring that's hot with noise from a lot of fantastic noise generators (computers, TV's, anything with a switching power supply).  You're almost always better off sticking something out a window, but if you have really severe restrictions, there's only one major rule you need to keep in mind:  Try everything and keep what works best.

My experience in an apartment was an obvious improvement every time I got the antenna wires further from the building, even if it was just a change of a few feet.  That's not a hard and fast rule, just my specific experience.  I ended up with 100ft of magnet wire in two legs about 50 feet each flung into some nearby trees.  One leg was almost straight out and the other took a couple of bends.  It was all fed by a remote tuner on my balcony : http://www.n3ox.net/projects/servo

A 10m antenna is small enough that you could stick it out the window pretty easily as a temporary thing... like an end fed half wave on a 16 foot fiberglass fishing pole.  Depends on what your apartment is like both in outside access and whether or not they actually care deeply about antennas. 
« Last Edit: June 05, 2011, 07:59:08 AM by N3OX » Logged

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

Monkey/silicon cyborg, beeping at rocks since 1995.
NU9J
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Posts: 109




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« Reply #2 on: June 05, 2011, 09:09:33 AM »

No way to predict; you'll just have to try it.

Some apartments (lots of reinforced concrete) are going to be opaque to RF or nearly so.  Others (wood and vinyl siding, townhouse type places) will be better, but performance will be a complicated function of wiring, plumbing and ductwork.

Indoor antennas will tend to be vastly more noisy than ones that aren't quite as tightly coupled to wiring that's hot with noise from a lot of fantastic noise generators (computers, TV's, anything with a switching power supply).  You're almost always better off sticking something out a window, but if you have really severe restrictions, there's only one major rule you need to keep in mind:  Try everything and keep what works best.

This apartment complex is old: wood slats + plaster walls + red brick. I wish I could stick something out the window, but the management will have issues with that. However, I can try it and leave it outside until someone says something.
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~Philip
W5RB
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« Reply #3 on: June 05, 2011, 09:22:08 AM »

Some years ago , I helped my friend John , then KG6MD , stretch a 20-meter dipole across the ceiling of his 2nd story apartment in Jackson , MS . He then connected a MFJ sideband rig , with output of about 15w PEP , checked SWR , and called CQ . The station that came back was in  FIJI ! I'd never have believed it , had I not been there .

Don't expect performance like this , but it can happen . Keep your power low to prevent radiating RF from getting in your rig , or in your TV, telephones, etc. , or your neighbors' electronics . Let us know how it works for you .
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WB6BYU
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« Reply #4 on: June 05, 2011, 09:59:15 AM »

I'd put the dipole across the ceiling if possible rather than the floor or the wall - gives it more height.

I've done this before both in a single-story house and a second-story apartment.  Neither worked particularly
well.  A 24' piece of magnet wire running out the window to a tree worked much better.

That's not to say it might not work for you - it is easy enough to build a simple dipole and try it out in
several places around the apartment.

Not only does antenna performance depend on the building materials, it also depends on the state of the
ionosphere.  Around 1960 or 1980 at the peak of the sunspot cycles you could work a lot of DX on 10m,
even with a mediocre antenna because the bands were in great shape.   At the moment we're still recovering
from  one of the deepest dips in sunspots in recent times, so conditions aren't as good.  But whatever
antenna you put up is likely to work much better in 3 years than it will now.
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N1LO
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« Reply #5 on: June 06, 2011, 10:55:38 AM »

It's a compromise, for sure, but try it. When 10 is open, it doesn't take much to make contacts.

Suspend it from the ceiling, keeping the wire a few inches from the plaster. The outer 25-30% of dipole legs has high voltage and readily interacts with nearby objects, detuning the antenna.

You can also let the last 1-2' hang vertically (inverted U) as tails to shorten the dipole span to as little as 12', as long as no one is in danger of touching the tails! (ZZzt!)

Indoor antennas work best with energy dense modes like CW and PSK31.

You can make an improvised apartment window dipole by sticking an 8' fishing pole with a wire out the window (at night) up at 45° and throw out an 8' wire hanging down for the other pole.

GL,

Mark
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N4NYY
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« Reply #6 on: June 06, 2011, 12:53:55 PM »

I would get it as high as possible, and as far away as possible, from the electrical wires.
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KE3WH
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« Reply #7 on: June 08, 2011, 05:27:48 AM »

Talk to the owner, he may let you place it in a better location. Unless of course the lease prohibits antennas, in that case might be best to go mobile.
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First ticket 1980. Ex KA3EWT, N3DSO.
AE4RV
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« Reply #8 on: June 08, 2011, 05:49:14 AM »

I would get it as high as possible, and as far away as possible, from the electrical wires.

Good advise. But at the end of the day I'd put it wherever I could and TRY it.
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NU9J
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« Reply #9 on: June 08, 2011, 07:45:42 AM »

Thanks for the replies so far.

Another question: what gauge and type of wire should I use for the dipole itself?
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~Philip
KE4JOY
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« Reply #10 on: June 08, 2011, 08:06:06 AM »

Thanks for the replies so far.

Another question: what gauge and type of wire should I use for the dipole itself?

Any really. even down to 18Ga willl work if your not running any power to speak of (100 watts). Stranded / solid very little differentc. Ive even seen them made from lamp 'zip' cord.

You mentioned plaster walls. Hope there isnt metal lath in them, another reason to string it up as high as you can get it.

Hope you dont have any RFI issues but 28Mhz in close proximity its going to be dicey.

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N4NYY
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« Reply #11 on: June 08, 2011, 09:19:38 AM »

Quote
Good advise. But at the end of the day I'd put it wherever I could and TRY it.

Before I got my ticket in 2005, I stuck a CB antenna in the attic with a ton of ground plane wires (ranch house). I actually got out fairly well, but my receive was noisy as hell. The proximity to electrical wires and noise from various electronic devices killed me. If you have a 2 story house, all the better. If you have I high attic like I had in my childhood home, a dipole would work fantastic.
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NU9J
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Posts: 109




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« Reply #12 on: June 08, 2011, 09:32:13 AM »

You mentioned plaster walls. Hope there isnt metal lath in them, another reason to string it up as high as you can get it.

Hope you dont have any RFI issues but 28Mhz in close proximity its going to be dicey.

No metal laths, only wood. The only RF sources in my apartment are a computer (which I can tell is going to annoy me at 28.636 MHz), and a 2.4 GHz 802.11g router.
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~Philip
KB1TXK
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« Reply #13 on: June 08, 2011, 11:44:22 AM »

I'd at least try a vertical, since 10m is close enough to CB. 

If it were me, and I was experimenting:

LARGE cookie sheet
3/8 x 24 magnet mount
102" radio shack stainless CB whip

trim whip to whatever part of 10m you plan on using the most
put in mag mount
slap mag mount on cookie sheet
put all but a couple inches of sheet out window
close window (holding the sheet in place)

If that works...figure out a way to temp-mount that cookie sheet so it doesnt fall on someone's head.  From there on out, just stick the sheet/antenna out the window when its time to play, remove when you're done.

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NU9J
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Posts: 109




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« Reply #14 on: June 08, 2011, 12:03:34 PM »

I'd at least try a vertical, since 10m is close enough to CB. 

If it were me, and I was experimenting:

LARGE cookie sheet
3/8 x 24 magnet mount
102" radio shack stainless CB whip

trim whip to whatever part of 10m you plan on using the most
put in mag mount
slap mag mount on cookie sheet
put all but a couple inches of sheet out window
close window (holding the sheet in place)

If that works...figure out a way to temp-mount that cookie sheet so it doesnt fall on someone's head.  From there on out, just stick the sheet/antenna out the window when its time to play, remove when you're done.

Lol. Awesome. I'll try that if the dipole doesn't work out so hot, but my coax and connectors just showed up at the front door. TO THE HARDWARE STORE!
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~Philip
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