|Type of antenna||Time for construction||Cost of material|
|The short longwire||5 minutes||50 cents|
|The longwire||15-30 minutes||3 euros|
|The Tuned Loop||1-2 evenings||3 euros|
|The FM Dipole||5 minutes||50 cents|
Waves and frequency. Let me first say a word about wavelength and frequency. These are related, but inversed: a higher frequency means shorter waves. Most radio stations list and advertise their frequency in kHz (kiloHertz) or MHz (MegaHertz) and kilocycles and Megacycles (kc and Mc) are used as equivalents. (The official standards prescribe the unit `Hertz' and also that the k for kilo is lowercase and the M for Mega is upper case!!) One MHz is 1000 kHz.
Long and Short waves. The Medium Wave has frequencies between 540 and 1610 kHz (wavelengths from about 180 to 55 meters), so we may find stations at 675kHz, 1008kHz, etc. In Europe all MW frequencies are multiples of 9 kHz while in America they are multiples of 10 kHz; I think the Far East uses the same as America. The FM band has frequencies that are much higher: 87500 kHz to 108000 kHz, and to make the figures more readable the frequencies are expressed in MHz: 87.5 to 108. The SW band has frequencies that are higher than MW, but by far not as high as FM. SW frequencies are roughly from 3000 to 25000 kHz, or 3 to 25 MHz. The Long wave band has smaller frequencies: 150-300 kHz.
Each transmission frequency relates to a specific wavelength. These are of interest for 2 reasons: older european radios calibrated the dials using wavelengths (no frequencies) and the wavelength is the basic unit to measure antenna dimensions. The wavelength (in meters) is found by dividing the speed of light (300,000 km/sec) by the frequency. So 675kHz means wavelength 300,000/675 = 445 meters and 98MHz (in the FM) is 300,000/98,000 = 2.94 meters. We observe that the MW frequencies correspond to wavelengths between 180 and 550 meters, the Shortwaves have wavelengths between 100 and 12 meters, and FM is around 3 meters.
With this simple 2m antenna the radio should receive, at DAYTIME, the local MW stations (those within ~300km distance) and usually some remote stations on Shortwave below 20m. After dark it should receive many MW stations, say those within 1000 km distance, and the shortwave band should receive plenty of stations. So the 2-3m wire should allow you to demonstrate the radio and to see that SW `works' for you.
The technical term for this type of antenna is `longwire', even though this piece of wire can hardly be called long.
Here in Europe, with such a wire one hears about 30 stations on Medium Wave during the day. At nighttime the signals on MW and SW come in so strongly that the radio may become overloaded. At many frequencies several stations will be heard simultaneously, which makes it difficult to understand anything. MW stations up to 2000km away can be heard... if they are lucky enough to have no strong transmitters on the same frequency closer to your house. Annoying noises can often be reduced, and desired signals increased, by grounding the radio: this is done by connecting the ground terminal of the radio to a water pipe.
So my longwire is just one wire, connected to the radio on one side and runs 20 meters away, and roughly horizontally. Depending on the geometric situation of your house and radio, you may experiment with other layouts, for example if you live in a highrise, you can have a vertical antenna by hanging 10-15 meters of wire outside your window downward! (Not all residence buildings allow this, unfortunately, and your downward neighbors may start wondering about what is running in front of their window. Not to arouse suspections you better take the wire inside after listening.) In any case, the best place for a longwire antenna is outside, and preferably high up. The house is usually filled with electromagnetic radiation from household appliances, and we prefer to have as little of this as possible in the radio. Also, the fields of radio stations are a lot stronger outside.
Old valve radios are built for long wire antenna's, so you can plug the wire end into the old radio directly. Modern radio's, such as the Philips D2999, have low impedance input and your wire will not work optimally. You can improve the result of your long wire antenna with an antenna tuner, like depicted on the left.
The 20m longwire is the best `all-band' antenna: if you want something better still, it will be a directional or tuneable antenna for specific bands, like a tuned loop or a dipole for the 15 meter or 20 meter band. But it is no use to start building anything beyond this 20m longwire before you feel the need to have something for a specific band.
A loop design is detailed on this page.
The one on the picture includes one of the co-constructors and a
crystal receiver; it's design is detailed here.
The splitted part of the wire picks up the signal, the other part is
just the feeding connection.
This type of antenna is called an open dipole and it is
directive in the direction perpendicular to the position of the antenna.
(Note: I received one email from somebody who said his T didn't work.
The problem turned out to be that I had not explicitly mentioned that
the bottom of the T should actually be connected to the radio in
The FM Dipole Antenna
Modern FM portables have whip antennas, which are hard to beat.
Some of the older tubed Fm radios have small built-in antennas and
your reception can be improved using about 2 meters of two-prone wire.
On one end of this wire you connect two banana plugs to fit the
antenna terminals of the radio.
At the other end you split the wire over a length of circa 75 cm, thus
forming a T-shape and
connect the split part of the wire to the wall or ceiling.
The splitted part of the wire picks up the signal, the other part is just the feeding connection. This type of antenna is called an open dipole and it is directive in the direction perpendicular to the position of the antenna.
(Note: I received one email from somebody who said his T didn't work. The problem turned out to be that I had not explicitly mentioned that the bottom of the T should actually be connected to the radio in question!!)