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W5ALT Indoor Vertical Antenna
A base loaded vertical antenna for use on all the
from 6 to 40 meters.
I have been operating from an apartment in
Maracaibo, Venezuela for over a year and during that time have worked well
over 100 countries, all 50 states on HF, and well over 100 grid squares on
6 meters mainly using CW, SSB and PSK31. Many people have asked me how I
get a signal out of an apartment, so this page will show my indoor
vertical antenna and explain how I set up a station that works well from
inside an apartment.
First, here are some thoughts on how a station
should be set up from inside an apartment. I want to point out some
important facts and dispell some common misunderstandings about antennas
You need a good
All I can say is that satellites, airplanes, and moving
vehicles usually don't have a ground connection. A good ground is almost
impossible from an apartment on the 9th floor. Instead, use a balanced
antenna design or use radials (or counterpoises, whatever you prefer to
call them) to balance an unbalanced antenna, such as a vertical. These
will not provide a DC safety ground, though. That's a different issue.
Short antennas won't work
That's simply not true. The principle of conservation of
energy applied to antennas basically says that whatever energy goes into
an antenna is either burned up in heat or radiates. Period. So, if you can
load an antenna and the resistive losses are low, it will radiate. The
trick is the low radiation resistance of short antennas, so you need an
efficient way to feed them.
An indoor antenna is
All I can say is that whoever says that without
knowing the situation is uninformed. Basically you need to do a radiation
safety check, but normally if the antenna is more than a few feet from
people, there's not much of a problem at typical power levels. For
example, I have a 100 watt transceiver which I normally run at 90 watts.
It's rated at about 50% duty cycle, but I never operate non-stop for more
than a few minutes. Most of us do a lot more listening than transmitting.
Check out your situation, but let's not get paranoid over nothing.
Good antennas are
complicated, expensive, etc.
There are those that want to
believe that, and I feel sorry for them, unless they are selling antennas.
Many simple antennas perform well and can be built from inexpensive
materials. My indoor vertical is just one example.
Although the design is fairly typical and I
claim nothing new, my indoor vertical was custom designed for my location.
The constraints are that it must fit into the corner of the room where I
operate, be unobtrusive to my wife and visitors, work well, and be easily
constructed. After playing with various designs and ideas, I decided to
build a base loaded vertical antenna with 2 radials for use on all the
bands from 6 to 40 meters. The size of the vertical element is 2 meters,
so it will comfortably fit under the ceiling in the room. The diameter was
determined by available aluminum tubing. The loading coil needed to be as
large diameter as possible to provide enough inductance for loading. The
dimensions were tweaked a little using MultiNEC antenna modeling and then
I started looking for parts.
The vertical element consists of 2 one
meter pieces of aluminum tubing used for hanging curtains. One piece is
1/2 in diameter and the other is 5/8 in diameter, so they could be
telescoped. There's nothing critical about the dimensions. I paid Bs 2000
for them at a hardware store in Maracaibo (about $1.50). The wire for the
radials and coil was also bought at the hardware store for about Bs 3000
(about $2.25) and consisted of 10 meters of 3 conductor #14 guage solid
copper house wire.
I was in a quandry about what to do for a coil
form and how to make a stand for the antenna. My wife found a small
plastic trash container that was very slightly tapered and about 5 1/2
inches in diameter and 1 foot long. Then, with her typical flash of
brilliance, she found a plastic toilet brush with a stand and said "Why
don't you put those pipes on this?" In fact, it worked out quite well! The
cost of the trash can and toilet brush stand was about another Bs 2500
(less than $2.00). Besides an alligator clip and a coax chassis mount
socket, the total cost of materials was around
Construction was quite
simple. The ends of the tubing sections were scraped shiny, slipped
together and joined with a small bolt. The loading coil was wound on the
plastic trash container. I cut a hole in the bottom of the trash container
to fit over the toilet brush and mounted it upside down on the brush
stand. The vertical element slipped over the toilet brush and a hole
drilled through the tubing and handle holds the whole thing in place. See
Figure 1 for a close up of the base.
Picture of antenna base
(Important, note that the bottom end of the
coil is connected to nothing
and does not show this in the
The ends of the radials were attached with small
hardware to a coax chassis socket and then run along the baseboards from
the corner where the antenna sits. A short wire with an alligator clip is
attached to the center conductor of the coax socket and used to tap the
loading coil. The whole thing is fed with standard 50 ohm coax from an MFJ
antenna tuner. The whole thing took about 1 afternoon to build and test.
Figure 2. The finished vertical in place
Tuning the vertical was accomplished by adjusting
the tap on the coil for lowest SWR on each band without the tuner. On most
bands the lowest SWR is around 2:1, which is marginally OK. After finding
the tap point, the tuner is used to tweak the match so the transceiver is
happy. I made some paper labels to stick on the coil to indicate the tap
So how does it
Well, without doing side-by-side comparisons, it's
hard to really evaluate an antenna. All I can say is that it tunes on all
the bands from 6 to 40 meters and I have worked the world. I am usually
able to get through DX pileups, although I know my signal is not the best
or strongest. The best indication of its perfomance is probably the QSL
cards that I've received, some of which are shown on another page here. In
the first 3 months using the vertical, I made over 300 contacts from about
50 countries. You decide if it works or not!
Walt W5ALT email for questions -