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Author Topic: 10th floor long wire antenna  (Read 2539 times)

Posts: 4

« on: August 16, 2012, 05:53:35 PM »

I am a rank amateur.  I live in a 10th floor condo in a building which knows nothing of amateur radio.  I want to run a wire partially around the building, hugging the brick.  from my window, one side could be as long as 40 feet and the other side 30 feet.  I will bring the feed in through the window.  I will have a good radio and a tuner.  Of course I want to work 20 to 80 meters.  Any suggestions, or should I just get one of those window mounts and a whip?

Posts: 3288

« Reply #1 on: August 16, 2012, 06:53:09 PM »


I would call your proposal more of a Random Wire, since it is only longer than a wavelength at 23Mhz and up.

I'm skeptical of the Miracle Whip clones and would rather experiment with wire than spend +$100 on one.  But some people have good luck and love them.  I'll 40ft of wire over a 3 foot whip any day

-40ft of wire one direction as the radiating element and 30ft the other direction as the counterpoise is not a bad set up.  You can also see it as a lopsided dipole too.  There is no way to model or predict how it will behave on any given band.  You may have RF all over, may be the building Channel Master on one band and not another.

-Do not tell anyone you are a ham or have radios nor let them see you working on antennas.
-Use insulated wire.
-I would feed with coax and use a 1;1 BalUn at the feedpoint to keep RF out of shack and reduce noise.
-Since overall ant. length is approx 70ft, 468/70ft=6.7Mhz, your tuner will be will be working hard to get below 40m.
-If you have RF in shack or apartment, make an additional 1/4wavelength counterpoise for that band and attach it to ground point on tuner. Insulated wire and end, run around baseboard of shack.
***Keep power low, 25watts for start until you are certain on each band you are not causing interference.  This will be difficult.  Better to an active mouse than a shut down alligator, or on the street!

This should get you started, bill

Posts: 1789

« Reply #2 on: August 16, 2012, 07:43:51 PM »

 Is there anyway you can run a very, very tiny gauge wire (preferably, stainless steel or bronze) out the window and down to a point on the ground that would be
 unnoticed? That would get the antenna out away from the building which has several advantages.  Agree, that, unless you are on VERY good terms with the building manager/owner, you want to act like a foreign spy who would be caught an executed !  If you start sticking poles, etc. out a window, somebody is likely going to come calling asking about it. It is much easier to get forgiveness than permission !!! If someone does ask, tell them it is a RECEIVING antenna only....don't talk about transmitting!

 Seriously, and respectfully: There is no way around this; you need good accurate knowledge of antenna theory and matching in your situation. Cold fact is that
 you are not in a "plug and play" QTH. You need to put in some serious study of the ARRL Antenna Book to get an idea of what type of antenna and feed method
 will likely work best. (You probably have several decent options.)

 Antennas are not complex, but they also are not forgiving of lack of knowledge, assumptions, myths and guesses ! Certain specific
 electrical parameters must be met for an antenna accept and radiate power efficiently. Bottomline:  the single best investment you could make at this point
 in your antenna system is the Antenna Book and some study time really getting a handle on antenna basics. In this case, knowledge is Power radiated !!
 Again, I mean the foregoing respectfully and as an attempt to help.

 Almost ANY place can be made to work as a QTH, but you MUST understand how you combine the physical/mechanical environment with a TYPE of antenna.
 .....and that takes some know how.

Good luck.  73,  K0ZN

Posts: 17423

« Reply #3 on: August 16, 2012, 09:10:40 PM »

The first problem is that brick is lossy, and more so when wet.  The further you can
keep your antenna spaced away from the brickwork, the better.

But that isn't the end of the world:  even a few inches spacing will help to some
extent.  Depending on how visible the brickwork is to other occupants, you may be
able to make some small pieces of wood that will jam into the gap between the
bricks (painted to match the wall) that hold the wire out a couple inches, or some
other method to provide a bit of spacing.

However, if the best you can do is to use a spit wad or a piece of a styrofoam
"peanut" jammed in the crack to hold the wire flat against the mortar, give it a try. 
It won't be particularly efficient, but you'll probably still radiate some power.  I've
made plenty of contacts running 1 to 5 watts, so with 100 watts to an antenna
that is 5% efficient, you're in the same ballpark.  (Operating at low power isn't
always easy, especially on SSB, but it can be done.)

I'd start by recommending magnet wire, the gauge depending on how close folks will
be looking at it.  Often sold by the 1/4 pound spool, something like #24 is hard to see
at 10 feet.  I don't recommending going much smaller than #32, or it is too fragile.
Just remember to scrape the enamel off when you go to connect to it.

Try to make both sides the same length:  30 feet should work 40m and up, and
if you can bend around the corners to accommodate 50' on each side you should
be able to load up on 80m.  Put the tuner as close to the feedpoint as possible
and run balanced line like 300 ohm twinlead.

If that doesn't work out, consider a telescoping fishing rod (they come up to 20' or
so) and and stick that out the window when it is dark.  You can use it to hold the
feedpoint of the antenna out away from the building, with the ends tied off via
lengths of black fishing line or heavy thread, or run an end-fed wire out the the
end of the pole then hanging down from there.  Something like 20' out and 35' down
should work pretty well for 80m through 17m, and perhaps other bands as well.
You'll need a tuner near where the wire enters the building and some sort of ground
system, which might be part of the building (I used metal window frames, which were
all tied together) or individual radial wires for each band laying on the floor under your
carpet or tucked around the walls. 

For either of these options, I'd suggest stranded, insulated hookup wire will
survive repeated flexing better than solid wire.  I use #18 to #24 or so, and
sometimes smaller.  It comes in many colors, so look for one that blends in with
the brickwork.  (An electronics surplus store may have lots of different colors
and sizes in stock - I've picked up a 1000' spool for a few dollars.)  The insulation
may start to crack after a couple years in the sunshine, but by the time you
need to replace it you may be planning the next version.

The balanced dipole will probably have fewer quirks and/or problems with RF in the
shack, but you'll just have to see what works best in your specific situation.
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