One of the most useful types of antennas is the outside wire antenna, commonly called an inverted L or longwire antenna. It consists of a horizontal length of wire mounted at some height above ground, with a vertical wire attached at some point along the wire. This is called the downlead and is generally as long as needed to connect to the device with which it is being used. Another lead, called the ground lead, is connected to the earth by means of a metallic rod, water pipe, or other buried conductor. The downlead and the ground lead are the two wires that are connected to the antenna and ground connections of the receiver or other device using the antenna system
A typical long wire antenna is shown in the above figure. This is simply a length of wire run from the house to a convienient support. Height H is typically 15 to 60 feet or more, although can be as low as 8 feet. Minimum height is limited by clearance required above ground, but 15 feet will clear most objects. The horizontal section called the flat top is supported between two convienient supports and does not need to be exactly horizontal. Any handy supports can be used. Try to get the antenna in the clear as much as possible. A mast is shown on the house to get more height, but most 2 story houses are high enough so the house itself can be used as one support. The flat top length L can be any convienient length, and is usually 25 to 200 feet as needed. Depending on your local conditions, wire size can be anything from #22 for very short runs to #12 or #10 for longer runs. Remember that mechanical considerations, wind and ice loading is a factor and will dictate minimum usable size. The downlead can be smaller, and usually #14 or smaller is adequate
MAKE SURE ANY UTILITY OR POWER WIRES ARE AT LEAST 10 FEET FROM ANY PART OF THE ANTENNA WIRE AND NEVER DIRECTLY ABOVE OR BELOW WHERE FALLING WIRES CAN MAKE CONTACT WITH THE ANTENNA SYSTEM. DO NOT EVER USE POWER POLES AS SUPPORTS. Keep antenna as far away as possible from telephone, cable TV, or power lines. This will ensure safety and freedom from electrical noise and interference.

Insulators can be standard glass or ceramic antenna insulators or made from short lengths of plastic pipe or as a last resort, wood dowels that have been boiled in paraffin wax. These are available from dealers in ham radio supplies, see web for suppliers.

The ground rod is a standard 8 foot 5/8 inch rod available from an electrical supply house. Get a ground rod clamp if not supplied with the ground rod. The ground wire is a short length of #12 or larger copper wire. A ground clamp is used on the rod to attach the copper wire to the ground rod. Drive the rod as deep as possible into the ground, at least 6 feet or more. Try to keep the ground lead as short as possible.

A metallic cold water pipe can be used as a ground if impossible to install a ground rod. DO NOT use an AC power ground as this is both hazardous and electrically noisy.

Where wires enter a building, use insulation over the wires. Stay away from any AC wires inside walls. If you are using a transmitter, a feed through insulator should be used on the downlead where it passes through the wall. It is a good idea (And a MUST in lightning prone areas such as in Florida) to install a lightning arrestor or some means to ground the antenna when not in use. An open knife switch is good for this purpose.

None of these dimensions are critical, but for best results on AM broadcast and low frequency bands, make as long and as high as possible. Leave a little sag in the antenna to allow for movement in the wind and to reduce mechanical strain in the wire. For general shortwave listening, Height H= 25 to 50 ft and Length L= 50 to 75 feet is a good length and will be found satisfactory with most AM and short wave receivers. Then the total length L + H will be between 75 and 125 feet, about perfect for most shortwave and amateur purposes. But if these lengths and heights are not possible, do the best you can. Even a 20 foot wire 10 feet high will work better than something inside the building. A small, short outdoor antenna is still better than any good indoor antenna