So when we refer to "wire" in the article and projects below, use the appropriate wire size.

OUTDOOR GENERAL PURPOSE MULTBAND SHORTWAVE (WORLD BAND) ANTENNAS

THE LONG WIRE SHORTWAVE ANTENNA

The simplest multiband shortwave antenna for shortwave listening is probably the longwire for most newcomers to building antennas. It is literally, a random long length of wire stretched out from the shortwave receiver antenna connection and attached with some form of an insulator on the opposite end.
No bells or whistles and usually very easy to do.
Your shortwave radio probably has either a short telescoping (pull-up) antenna and or a connection point for an external antenna usually on the rear.
A very simple method of drastically increasing the signal strength to your shortwave radio is to simply add about 50 to 70 feet or more of insulated wire of small diameter, (size not critical, it must support it's own weight), attached to either the telescoping antenna with an alligator clip or a suitable connector to the rear external antenna connection and stringing it out across or from the house to the appropriate support as high as possible on each end with some form of insulator along the entire length, (a non-metal device that will not pass electricity). In other words, don't run it along a water pipe, conduit,  metal house siding, rain gutters, etc. It can be tacked along the ceiling or snaked up into the attic or around the roof. Just don't run it close to metal. Use your imagination. Make sure that you have removed the insulation when adding the connector or alligator clip.

DANGER! DO NOT STRING THIS ANTENNA OR ANY ANTENNA OVER, UNDER or NEAR ANY ELECTRIC POWER LINES OF ANY TYPE! YOUR LIFE WILL BE IN YOUR HANDS, NOT MINE and I assume no liability. Repeat....never OVER, UNDER or NEAR POWER LINES! This includes the service drop wire from the utility power pole to your electric meter! Have adequate space allowed to insure that if a power line falls, it will not fall on your shortwave antenna! Use this rule of thumb....
If it is under the power line......the power line WILL FALL! If it is over it,
the antenna WILL FALL! You don't want either happen!

Now back to shortwave antennas.
The longwire type of antenna is a compromise as ALL antennas are. Don't expect the same reception 100% of the time from the same station. Mother nature and man-made variables will surely destroy your expectations.
This type of antenna generally "picks up" stations better in the direction of the wire, so if you live in the U.S.A., you can string it in a Northeast Southwest direction and get the European stations somewhat better. Don't worry if your layout is not perfect....just put it up and have fun listening.

THE MULTIBAND LONG WIRE SHORTWAVE ANTENNA
A Much Better But More Complicated Antenna

This antenna is end supported and designed to receive the major shortwave bands between 90 meters and 16 meters. It uses only 4 wires and a unique antenna property called harmonics to get 8 bands using only 4 wires! Again, it is a compromise but an excellent performer....the perfect antenna does not exist. We "Hams" are working on it constantly!

After construction, this shortwave antenna should be stretched out in a straight line as high as possible as in the long wire antenna above, and about 140 feet straight out from the house! Don't fret! If you cant', you can't. Utilize your existing space. More supports may be required for a zig zag layout but performance may suffer a bit. Don't worry, it will certainly outperform that built in poor excuse for an antenna!

It consists of 4 separated insulated wires, (measurements below), all connected (soldered) on one end, leaving the opposite end unconnected and insulated at the support. If you do not know how to solder, then scrap all the coating from the wire down to bare copper and tie the ends together using several knots. You really should learn to solder though!. This will make for a more permanent and much better electrical connection.
The soldered end must be between an insulator and the radio for mechanical strength.
You don't want much stress on the soldered connection other than the coax leading to the radio.  The end that has all wires connected should be soldered to the center wire of a suitable length of 50 - 75 ohm coaxial cable leading to the short wave radio with a suitable connection. A ground wire is soldered to the shield only of the coax at the same end that you soldered all the wires together and attached to a ground rod driven into the ground near the house. Seal and tape all outdoor connections from the weather. This antenna is called an end fed half wave antenna.
See picture, formula and wire measurements for bands below:
(The lengths are not extremely critical, but try to get them as close as possible.)

Note: In the instruction box above, the last sentence refers to the long portion of the wires, not at the connection point to the coax feed line to the receiver. All wires are connected together at the connector center conductor wire!

(frequencies shown below are approximate shortwave band centers):

Wire 1  (LONGEST WIRE) 3.25 MHz (90 meter band) 09.75 MHz (31 meter band 3rd harmonic)
468 divided by 3.25 = 144' 0"

Wire 2  3.95 MHz (75 meter band) 11.85 MHz (25 meter band  3rd harmonic)
468 divided byi 3.95 = 118' 6"

Wire 3  5.10 MHz (60 meter band) 15.30 MHz (19 meter band  3rd harmonic)
468 divided by 5.10 = 91' 9"

Wire 4  (SHORTEST WIRE) 5.90 MHz (49 meter band) 17.70 MHz (16 meter band  3rd harmonic)
468 divided by 5.90 = 79' 3"
The number 468 divided by the frequency above is the formula for calculating a half wave antenna length used all the time by Amateur radio operators in building many different kinds of antennas.
You'll need about 435 feet of wire for this antenna plus appropriate length of coaxial cable.
Check with Lowe's, Home Depot, Radio shack, Wal Mart, farm supply stores and other stores that might have wire bargains. Dual conductor speaker hookup wire can be purchased in rolls and split in half to double the length. Multiconductor tv antenna rotor wire can be used the same way. Electric fence wire is also a good alternative.

The wires are spread 3-4 inches apart, held in place with simple non-conductive spacers.
Just cut a few pairs of the acrylic, Plexiglas, plastic strips or other non-conductive material that will not be damaged by moisture long enough to attach the wires keeping the spacing about 3 to 4 inches or further if you want.
Use your own ingenuity with the attachment method while keeping them separated. 
To accomplish all of this, you stretch the antenna on the ground, assemble it, then get it up to the support with your own best way.

OUTDOOR CENTER FED MULTIBAND (FAN) DIPOLE SHORT WAVE ANTENNA
NOTE: For use with the higher quality table model communications receivers that have standard antenna connectors capable of using direct coaxial cable connectors.

This antenna type is used by many Ham Radio Operators worldwide and is very popular but the lengths for the Ham bands are entirely different.
The entire length of the antenna is about the same as the one above and the coaxial cable is connected in the center of the span with the center conductor connected to one side of the antenna and the shield connected to the other side then at the other end, to the receiver.
The formula used for this antenna is the same as the Multiband Long Wire above:

468 / by frequency in mhz = total length in feet. This resulting length is cut in half!

One antenna per band stacked.

It is somewhat more complicated in construction due to the center connection and requires support in three places....each end plus the center. The preferred method for using this antenna is drawn in the picture below with the wires "fanned" apart with at least a foot of separation between the ends.
All of the wire elements can be close spaced but some interaction will occur. Insulated wire is best so the individual wires do not connect on the longer lengths of the antenna.

Choose the antenna of your choice depending on your constructions skill and needs.
Either way, they both will be much better than the little telescoping antenna that comes with most portable receivers.

The center fed multiband dipole antenna (drawn below) consists of 2 separate sections of 4 wires on each side of the center connection at the support consisting of 4 wires connected to the center conductor of the coax and the other 4 connected to the shield.

In this arrangement, one half of the antenna is feeding the center conductor and the other half is feeding the shield. Each side must be insulated....not connected....to the other side. The other end of the coax is connected to the radio with the appropriate connector.
Use lengths in the above multiband antenna with total length split in half using the formula....half on one side and half on the other for each wire length per band. The coax can be anything from 50 ohm to 75 ohm.
Not critical on receive! You will have to use the proper connector on the end of the coax for your receiver antenna jack.