Probably the best DX site in the world
 DX news
Practical indoor antennas for everybody

HF Indoor Antennas:
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  

These 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 coax/BALUN connection.

  ======================================  Aluminium
       |------------------------------||                                                    foil
       | ===============================
       |-------------------------------------- Copper tape

This folding 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.

VHF/UHF Discones

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 it's in.
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
  -----------||--|-------------|----------|--||----------- || | | | || || | | | || || | | | || -----------||--|-------------|----------|--||----------- || | | | || || | | | || || | | | || -----------||--|-------------|----------|--||-----------

Aside 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.

               |                                  |
               |                                  |
           ----|----------------------------------|---- BOOM 
               |                                  |
               |                                  |

For horizontal 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 boom.
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

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.

These texts were postings that have been collected from Ham_Tech by Wayne M. Sarosi, KB4YLY. Hermod Pedersen has edited them for online publication for the
Front page
DX News
Andes DX
DX Lab
In Print
Web Stories

Web Archive
Mail Archive

Search all HCDX
mail since 1995

 About us
About us
Write to us

HCDX mail list

antennX  Cebik  FM antennas  Werner's links  Antenna Elmer  Coax basics