indoor antennas for everybody
Some practical indoor antennas that can be built by anyone:
** HF foil antennas
** VHF/UHF discones
** Wire beams
** Attic VHF/UHF rotables
** Tape antennas
** Telescoping VHF/UHF indoor beams.
HF Foil Antennas
HF foil antennas are too weak in their physical construction
for outside use. Foil antennas are just what the title implies,
foil. They are made from ordinary aluminium foil, the kind used
for heavy duty cooking, such as roasting a turkey.
This antenna goes in the attic of your home or condo. Apartment
dwellers may have a time with this antenna depending on their
location within their complex.
Materials needed are two to three rolls of aluminium foil, copper
tape with electrically conductive glue, a staple gun and staples,
and coax with connector.
By stapling the foil in a loop or dipole configuration on the
attic rafters, a simple antenna can be formed.
|| balun if desired
| coax to shack
|| Balun if desired
| coax to shack
two configurations are excellent when used with a tuner for
the various bands on amateur radio and SWL listening. They are
cheap to install and can be made into other configurations, by
the amateur, if desired. A relay can be installed to provide dual
antenna configurations if needed. With this device you can switch
between a dipole and the loop for different propagation conditions.
Size and shape is dependent on the attic structure.
Connections from the foil to the coax or BALUN are via the copper
tape. There are copper tapes available on the market that are
used for EMI applications. These tapes are expensive so if you
can get a piece of some of that tape from a buddy, it will work
wonders for you.
Otherwise, there is a trick with regular copper tape and the aluminium
foil that you can do. It's a simple folding technique that insures
a good connection and yet requires no soldering except for the
|-------------------------------------- Copper tape
method insures good contact on more than one surface. One
warning, do not leave air gaps, as it will have a capacitive effect.
Solder doesn't stick to Aluminium foil very well. With enough
heat, you can solder anything. Too bad the aluminium foil won't
hold up at that temperature and neither will the solder.
You now can solder leads to the BALUN or solder the coax direct
to the copper tape.
For an indoor antenna, the foil antenna works rather well. It
can out perform a vertical and pull in the weak ones with ease.
I think you'll find it one of the most inexpensive antennas you
can build yourself.
The discone antenna is a rather unique antenna for VHF
and UHF. The discone has no gain to speak of, yet can provide
the user with a range of ten times the design frequency for reception
and transmissions. This means that a discone designed at 140 MHz
will work fine up to 1.4 Ghz.
Hiding the discone outside may prove to be quite a feat. Unlike
most antennas, the discone has a large skirt and is tall to boot.
Its shape can draw attention. If you can place the antenna outside,
it will give you excellent coverage over its range. Inside, the
discone works well minus the attenuation caused by the building
There are many Discones available on the market if you choose
not to build one. Building one can be fun if you take the time
and lay everything out ahead of time.
There are a couple items I would like to point out about discones.
1) The gap between the top-hat and the skirt is critical.
2) The area under the skirt is a null to the antenna.
Design parameters are easy.
** The top-hat diameter is:
(0.1778 * (984/f MHz))*12
Example: at 140 MHz --> (0.1778 * (984/140))*12) = 15-in
** The diameter of the skirt, at the base, equals the length
of the skirt elements. This gives the user the closest impedance
50-ohms. Thus a skirt element length is:
(0.2675 * (984/f MHz))*12)
Example: at 140 MHz --> (0.2675 * (984/140))*12) = 22.56-in
** The gap is:
(0.007114 * (984/f MHz))*12)
Example: at 140 MHz --> (0.007114 * (984/140))*12) = 0.6-in
A tin funnel works well as a starting base, to which you
can solder brass skirt elements. A SO-239 chassis connector can
be fit into the cut-off funnel end and the top-hat soldered to
the centre pin of the SO-239. Insulating spacers can be used to
strengthen the gap. I've used a brass screw that was soldered
between the centre pin and the top-hat, but you can use anything
that you can solder.
Wire beams indoor
For many of us, the antenna is the biggest problem. Radio
fans have to contend with neighbours and the XYL in order to pursue
their hobby. An interesting HF and VHF idea I've seen used is
the wire beam.
The wire beam is unrolled and suspended in the direction required
for operation. After the operation is complete, the wire beam
is rolled up and stored for the next time. This type of beam is
excellent for 10m and up to 1.25 m. You may be able to set up
a wire beam for frequencies below 10m if you have the space to
do so. This antenna is also excellent for suspension in an attic.
A simple model is shown below:
R DE D
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from the elements, the rest of the configuration is non-conductive.
Wooden dowel supports are outside the ends of the antenna and
string/rope can be used to support the elements. The wooden dowels
are not required if suspension is taught.
You can see that variations of this set-up can be incorporated
to accommodate most any frequency from 10 to 1.25 meters.
Attic VHF/UHF Rotables
In many instances, a listener can mount a VHF or UHF beam
in the attic, on a rotor. They can achieve good results depending
on their location and height off the ground. Antenna size limitations
are solely dependent on the available room in the attic that allows
rotation of the beam without hindering its rotation.
To check the attic for the maximum size antenna, the hobbyist
must first enter the attic and measure the distances in the area
planned for the set-up. Trusses, electrical wiring, air conditioning
/ heating ducts, and the items that are stored up there, can all
play a factor in the actual antenna size.
Finding your antenna with a pair of long johns dragging off the
front end is not a pretty sight.
After measuring the area in the attic, the antenna size and height
off the attic cross members can be accomplished. Remember to allow
for a base to accommodate the rotor. This too must be calculated
into the system.
Building a sleek system, to rotate two or three small beams, can
be dashed, when the system will not turn because of an oversight
in the measured values of the attic area in question.
Turning radius is the important factor. Each antenna forms a rectangle
ABCD where the maximum distance is AD or BC.
antennas, the turning radius is from the mounting point to
the tip (either side) of the longest element. Multiple this figure
by two for the turning diameter of the antenna.
For vertical antennas, the truss angle places the biggest problem
as the height from the boom to the tip of the reflector (B or
A). In essence, this will shorten your boom length or require
a lower rotor mounting.
Indoor telescoping beams
One problem I have encountered from listeners living in
apartments is the space to place a VHF/UHF antenna. This concerns
operation of the beam from a bedroom or porch. In these cases,
the listener can not keep the antenna up and must remove the antenna
after he or she finishes.
Using telescoping elements can solve the problem. Adding a two
or more section boom can further the portability for the antenna
making it idea for field day, camping, or travel also.
Dimensions for beams have been discussed earlier, so I won't rehash
them here. The best portable and quickest for set-up is the four-element
VHF antenna. A two-section quick clamp boom with mounting flange
for a camera tripod provides the base. Each element contains two
telescoping units and a snap on fitting for attachment to the
The antenna described here can be stored in a briefcase save the
camera tripod. A VHF four-element antenna can provide 9dBi of
gain for the apartment dweller.
Tape antennas on sun-film windows:
Using the tape loop, discussed earlier, I tested the antenna on
two types of sun-film windows. The first was a plastic film, often
used in states such as Florida. There was no significant pattern
or gain change for the antenna. The second type of film is the
metal film sun screen.
Results here were dramatic. The pattern was severely disrupted.
Be sure that your window films are not the metallic type if you
plan to use indoor VHF/UHF antennas pointed out the window. The
metallic film acts like a reflector to the signal. Attenuation
is a strong factor concerning propagation. Some plastic films
appear metallic, but may not be.
Tape antennas on screened windows:
There are three types of screen used as screening for windows.
Plastic, fibre, and metal. The first two show some attenuation
of the gain and pattern shape is similarly effected. Basically,
the addition of the screen frame effects the VHF spectrum greater
than the UHF spectrum. The screen frame size is near the size
of VHF loops at frequency.
were postings that have been collected from Ham_Tech by Wayne M.
Sarosi, KB4YLY. Hermod Pedersen has edited them for online publication