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Author Topic: Random Wire / Long Wire Antennas for Apartments  (Read 4038 times)
N1IRF
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Posts: 39




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« on: March 21, 2013, 10:37:40 AM »

I am interested in constructing either a random wire and/or long wire antenna to operate the HF bands.  I live in an apartment and there are antenna restrictions.  I will also be using a ldg electronics Z-100 Plus antenna tuner with a RBA-4:1 balun.  Is it feasible to build an indoor apartment?  Are there any plans or designs I can use as a reference?  It also may be possible to construct a stealth long wire or random wire antenna outside.  I have about 60 to 70 feet length and about 10 to 15 feet height to work with.  What wire gauge is recommended (12, 14, or 16)?  I would also like to get some advice on grounding.  I have access to a cold water pipe; but. is this recommended?  Thanks.     
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WB6BYU
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« Reply #1 on: March 21, 2013, 01:13:28 PM »

Quote from: N1IRF
I am interested in constructing either a random wire and/or long wire antenna to operate the HF bands.  I live in an apartment and there are antenna restrictions.  I will also be using a ldg electronics Z-100 Plus antenna tuner with a RBA-4:1 balun.  Is it feasible to build an indoor apartment?  Are there any plans or designs I can use as a reference?  It also may be possible to construct a stealth long wire or random wire antenna outside.  I have about 60 to 70 feet length and about 10 to 15 feet height to work with.  What wire gauge is recommended (12, 14, or 16)?  I would also like to get some advice on grounding.  I have access to a cold water pipe; but. is this recommended?  Thanks.     


While it is possible to install an antenna indoors, performance can vary a lot
depending on the building construction.  Reinforced concrete, aluminum siding,
and stucco (which contains a layer of chicken wire) are not conducive to
good performance from inside.  Wood construction isn't too bad if it doesn't
have a lot of wiring and/or foil-backed insulation.

I've used a number of end-fed wire antennas from apartments.  My general
approach is to run the wire right to a manual tuner near the entry point (usually
through a window).  I'm not sure where the idea of using a balun came from,
but I've never bothered with one and don't see much reason for it.  (Of course,
my favorite wires are multiples of 1/2 wavelength, which doesn't always work
well for relay-switched autotuners due to the high voltages, though a simple
L network with a variable capacitor and manually tapped coil will work just fine.)

#16 wire is much larger than you need.  When you get down to #32 the birds
can't see it in time to miss it and you end up needing to replace it more often,
but the range of #22 to #28 or so gives you plenty of options to work with
without it being too noticeable.  You may be able to find wire with plastic
insulation in a color that blends in with the background, though the insulation
may degrade in a couple years in the sun.

One of my best apartment antennas was 130' of wire running down the roof
from my unit at the end of the building.  I got up on the roof in the middle
of the night and tucked it under the shingles, then dropped the end down
to my window.  That used salvaged telephone wire soldered together because
it was all I had at the time.  But you have to decide what supports are
available and accessible to you without excessive risk to your health and
housing.

The best ground I've found is a metal window frame, as all the windows
in the unit were bonded together.  A cold water pipe or radiator might work
in an older building where all the pipes are metal, but these days they often
include plastic.  My approach has been to do the best I can, then if I still
have RF-in-the-shack problems I add a quarter wave radial wire to the back
of the tuner and/or the rig and string it around the room for the bands that
aren't cooperative.

You may also have to experiment with wire lengths that your tuner will
match:  the theoretical lengths for multiples of half a wavelength don't always
line up exactly when you have wiring, ducting, downspouts, etc. affecting
the tuning.
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N1IRF
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Posts: 39




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« Reply #2 on: March 21, 2013, 01:53:17 PM »

Quote
#16 wire is much larger than you need.  When you get down to #32 the birds
can't see it in time to miss it and you end up needing to replace it more often,
but the range of #22 to #28 or so gives you plenty of options to work with
without it being too noticeable.  You may be able to find wire with plastic
insulation in a color that blends in with the background, though the insulation
may degrade in a couple years in the sun.

Thanks for the information.  I was wondering about the wire gauge and the amount of transmitting power.  I plan on using no more than 100 watts.  Could that be an issue with #22 to #28 gauge wire?
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N4CR
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Posts: 1694




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« Reply #3 on: March 21, 2013, 02:25:48 PM »

I was wondering about the wire gauge and the amount of transmitting power.  I plan on using no more than 100 watts.  Could that be an issue with #22 to #28 gauge wire?

That will not be a problem.

You also might want to look into magnetic loop antennas.
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73 de N4CR, Phil

Never believe an atom. They make up everything.
WB2WIK
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Posts: 20636




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« Reply #4 on: March 21, 2013, 02:34:24 PM »

I was wondering about the wire gauge and the amount of transmitting power.  I plan on using no more than 100 watts.  Could that be an issue with #22 to #28 gauge wire?

That will not be a problem.

You also might want to look into magnetic loop antennas.

I agree for most applications of "long(ish) wire" antennas, wire gauge isn't critical -- as long as it doesn't break, it should be fine.

But for a small loop (like a magnetic loop), wire gauge is very critical and you want it to be BIG because the current is high and conductor losses can be huge.

Two different kinds of antennas.

One thing that's worked pretty well for me as a temporary indoor solution is the MFJ Loop Tuner with as large a loop as I could physically fit in the available space, whatever that was.  I have one of these: http://www.mfjenterprises.com/Product.php?productid=MFJ-936B and when used with a loop made of #10AWG insulated copper wire just tacked up a wall, across the ceiling, down another wall, and back to the tuner -- it makes contacts!  Pretty easily.

Depends on a lot of variables, like what the walls are made of and the structure's exterior siding, etc.  But it's sure better than no antenna, and you can make your loop various ways and shapes to experiment, while using the same tuner.

Note this is not a regular "antenna tuner," most of which are L-matches or T-matches.   This is a special balanced tuner for loops and won't work with a coax-fed antenna.  The loop connects directly to the tuner, without a transmission line.
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W5WSS
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Posts: 1775




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« Reply #5 on: March 21, 2013, 09:05:46 PM »

The vertical loop fed in the middle of vertical dimension leg along with the loop balanced tuner will probably allow a lower TOA than a horizontal radiating indoor version.
I did a 66ft vertical version that I pressed into multi band service and provided better longer range DX utility than any horizontal version.
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KQ6Q
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Posts: 991




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« Reply #6 on: March 21, 2013, 09:47:51 PM »

While you're still looking, consider the PAR EndFedz antennas - one of those might be just what you need, ready to go, rather than going through the cut and try process and stirring up curious neighbors....
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N1IRF
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Posts: 39




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« Reply #7 on: March 22, 2013, 12:14:22 PM »

The other issue that I need to consider is grounding the antenna.  The apartment is in an old building on the first floor; and, I have access to the cold water in the basement.  If that doesn't work, I may need to use a grounding rod.  Does anyone have any advice or comments about grounding either a random wire or long wire antenna?

Also, I have read that some random / long wire antenna use a counterpoise.  Is this something I need to consider?   
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N3OX
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Posts: 8847


WWW

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« Reply #8 on: March 22, 2013, 12:33:28 PM »

Also, I have read that some random / long wire antenna use a counterpoise.  Is this something I need to consider?   

I lived in an apartment for many years and used a few different antennas made of very fine magnet wire, maybe 30AWG, as stealth outdoor installations. I fed a wire against the railing on my balcony for a while, which worked okay, but the whole thing worked much better when I switched to TWO legs fed as a long, slightly off-center-fed doublet.

Removing all connection to the building helped my noise somewhat.

I put a remotely controlled tuner on the balcony in the middle of the two wires (actually connected with a short length of parallel transmission line made of the two wires)

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

Worked pretty well.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WB6BYU
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Posts: 13486




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« Reply #9 on: March 22, 2013, 01:06:14 PM »

Quote from: N1IRF

The other issue that I need to consider is grounding the antenna...



There are multiple types of "grounds" that serve different purposes.  In some
cases a "ground" optimized for one purpose won't work for a different one, so
you need to define what sort of ground you think you need.

The most common ones are:

1) RF Safety ground.  This prevents a shock if the AC power line inside the
radio is shorted to the case, and some other conditions.  Generally the third
wire on the AC outlet is sufficient for this.  (It would have prevented my
making the patio door frame live with 120VAC to ground one time.  Fortunately
nobody was hurt.)

2) Lightning ground.  This diverts as much energy as possible to ground outside
the house in case lightning hits your antenna.  Proper lightning protection is not
for the timid, but there are hams whose antenna systems are hit several times
a year with no damage to their indoor equipment.  Whether or not you need
to worry about this depends on your antenna placement and the likelihood of
lightning strikes in your area.

3) RF ground.  There are a couple variants of this.  Basically it provides a
connection for the other side of your feedline:  just as with a battery
circuit, you don't get any power to flow if only one wire is connected.
However, in the case of RF on coax, without an explicit connection to the
coax shield the "other side" of the RF will flow back up the outside of the
feedline.  That can cause various quirks such as "RF in the shack", poor
audio, keyers with a mind of their own, etc.

A good RF ground is an important part of an end-fed wire antenna, though
the impact will vary depending on the relative wire length in wavelengths.
When the wire is 1/4 wavelength (for example, about 64' on 80m) then
maximum current is at the feedpoint, and any effective resistance can
greatly reduce the radiated power.  When a wire is a multiple of 1/2 wave
(the same length of wire used on 40m or 20m) then the feedpoint is a high
impedance, where current is minimum.  In this case, losses due to a poor
ground don't affect the efficiency as much.  (This is why end-fed half wave
antennas are popular, at least for those who are NOT using a relay-switched
autotuner.)  But at the same time the voltage across the antenna feedpoint
is higher.  Still, if you don't provide a low impedance path for the "other side"
of the RF to flow, it will go back along the outside of the coax.

Making a low impedance "ground" connection isn't as easy as running a wire
to a ground rod, however, when the length of the connecting wire is a
significant portion of a wavelength.  A perfect ground connected to the
antenna feedpoint using 1/4 wave of wire (about 8' on 10m) presents a
high impedance, and acts like no ground at all.  Ideally for HF operation
the connecting wire would be less than 3' long, which isn't always practical.

The common solution is to connect a quarter wave wire to the ground side of
the coax at the feedpoint and string it around the room.  You probably will need
multiple wires to handle several bands, though you might find that some aren't
needed (the 40m wire may work on 15m.)  These are often called "counterpoises",
though that term is not well defined and gets applied to an assortment of
configurations.  This provides a (relatively) low impedance so that most of the
RF flows into the wires rather than back along the coax.


At least that is a simple explanation.  Whenever the topic of grouding comes
up you get a lot of disagreement, often because some posters are assuming one
or another type of ground.

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W5WSS
Member

Posts: 1775




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« Reply #10 on: March 24, 2013, 02:34:27 PM »

Yes Dale, When I built and used an end fed wire from a summer cottage In my specific case, I used a very short 3ft section of 300 ohm balanced line from the auto L- tuner which was located at the inside interior corner of the window sill and out under the window pane and once outside the height was held tightly at an elevation of 5ft.
The line connected to the center connector of the SO-239 and junction-ed to the end fed antenna wire while the other leg of the line junction ed the shield lug of the tuner to a series of pairs of tuned 1/4 wave radials traveling in opposite and downward and sloped to insulated anchors on the far ends of each.

I was able to note that in this case when even a very short length fat large conductor was installed to a single brand new shiny 8ft earthing rod for safety purposes noise ingress was noticeable and problematic at the location and eventually disconnected for a wander lead contingency.

The antenna system was eventually developed and became really quiet and the antenna wire length was eventually purposely held to  between 1/4 wave length  and no longer than 5/8 wave.

Yes an all wire system but when we add these radials we change from end fed to center fed where the junction becomes the central reference point relative to feed point position I liked it.
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