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Ladder line is a specific type of transmission wire designed to reduce signal loss. Several defining features set it apart from other kinds of transmission lines, especially when compared to regular twin-lead. In many do-it-yourself (DIY) projects, another kind of ladder line, called an open-wire line, might be used. There are several applications for this kind of line, typically within radio transmission tasks. It can offer some considerable advantages and some disadvantages when compared to other transmission wires.
Twin-lead, in general, has certain characteristics that are the same as ladder line. This can include parallel copper or copper-coated wires held an equal distance from one another with some sort of insulator. Amateur radio stations often rely on twin-lead to connect their equipment and help with transmission or receiving.
Ladder line is a special kind of twin-lead consisting again of parallel wires connected by some sort of consistent insulator. In many cases, plastic webbing is used to maintain the space. What makes this wire unique, however, is that there are windows of material taken out of the insulator to reduce signal loss and other dielectric effects. This feature creates the characteristic ladder appearance.
Open-wire line is similar to this wire except, instead of a consistent sheath separating the wires, evenly spaced insulators typically maintain the parallel wires. Like typical twin-lead, these insulators can be plastic but are often ceramic, which can offer significant impedance levels. Many times, DIY projects make use of open-wire line because they can be simple to construct and fit into certain transmission requirements.
There are several applications for ladder line, typically within projects concerned with radio frequency transmission. It was historically used for television antennas, though much of this technology has been replaced. FM and ham radios typically depend on some sort of twin-lead to make the connection with receiver antennas.
Generally, ladder line is considered to have several advantages and some disadvantages over other forms of transmission cable. Over twin-lead, a ladder line will typically have less signal loss and interference while in use. Regardless, as with many types of transmission wire, it is prone to interference, especially when parallel separation of wires is broken. Ladder line also can be challenging to configure, because they must be a proper length so as not to interfere with passing radio signals. It also must be kept from direct, sustained contact with metal, which can cause significant signal loss if left unchecked.