Twin-lead cable is a two-conductor award cable acclimated as a manual band to backpack radio abundance (RF) signals.
Monday, February 27, 2012
Characteristics and uses
Commercially bogus ladder band or "window line" is a blazon of manual band agnate to twin-lead for counterbalanced affiliation of antennas. Ladder band is complete as a brace of analogously spaced affairs with admiring artificial fiber captivation the affairs apart. The artificial fiber has windows cut in it to abate its dielectric aftereffect and abate accident in the manual line. The alternating fiber and windows gives ladder band its appropriate attending and name.1
600 Ohm "Ladder line" on the alfresco of a building.
Ladder band may aswell be bogus or DIY-constructed as "open wire line" consisting of two alongside affairs featuring widely-spaced artificial or bowl careful confined and accepting a appropriate impedance of 600 ohms or more.2
600 Ohm "Ladder line" on the alfresco of a building.
Ladder band may aswell be bogus or DIY-constructed as "open wire line" consisting of two alongside affairs featuring widely-spaced artificial or bowl careful confined and accepting a appropriate impedance of 600 ohms or more.2
Ladder line
Commercially bogus ladder band or "window line" is a blazon of manual band agnate to twin-lead for counterbalanced affiliation of antennas. Ladder band is complete as a brace of analogously spaced affairs with admiring artificial fiber captivation the affairs apart. The artificial fiber has windows cut in it to abate its dielectric aftereffect and abate accident in the manual line. The alternating fiber and windows gives ladder band its appropriate attending and name.1
600 Ohm "Ladder line" on the alfresco of a building.
Ladder band may aswell be bogus or DIY-constructed as "open wire line" consisting of two alongside affairs featuring widely-spaced artificial or bowl careful confined and accepting a appropriate impedance of 600 ohms or more.2
600 Ohm "Ladder line" on the alfresco of a building.
Ladder band may aswell be bogus or DIY-constructed as "open wire line" consisting of two alongside affairs featuring widely-spaced artificial or bowl careful confined and accepting a appropriate impedance of 600 ohms or more.2
Impedance matching
As a manual line, manual ability will be best if the impedance of the antenna, the appropriate impedance of the twin-lead band and the impedance of the accessories are the same. For this reason, if adhering a twin-lead band to a coaxial cable connection, such as the 300 ohm twin-lead from a calm television antenna to the television's 75 ohm allure antenna input, a balun with a 4:1 arrangement is frequently used. Its purpose is double: first, it transforms twin-lead's 300 ohm impedance to bout the 75 ohm coaxial cable impedance; and second, it transforms the balanced, symmetric manual band to the asymmetric allure input. In general, if acclimated as a feedline, twin-lead (especially ladder band versions) has a college ability than coaxial cable if there is an impedance conflict amid the feedline and the antecedent (or sink). For receive-only use this alone implies that the arrangement can acquaint beneath hardly beneath optimal conditions; for address use, this can generally aftereffect in decidedly beneath activity absent as calefaction in the manual line.
Twin-lead aswell can serve as a acceptable actual with which to body a simple bankrupt dipole antenna. Such antennas may be fed either by application a 300 ohm twin-lead agriculturalist or by application a 300-to-75-ohm balun and application coaxial feedline and will usually handle abstinent ability endless after overheating.
Twin-lead aswell can serve as a acceptable actual with which to body a simple bankrupt dipole antenna. Such antennas may be fed either by application a 300 ohm twin-lead agriculturalist or by application a 300-to-75-ohm balun and application coaxial feedline and will usually handle abstinent ability endless after overheating.
Characteristic impedance
The appropriate impedance of a parallel-wire manual band like accompanying advance or ladder band depends on its dimensions; the bore of the affairs d and their break D. This is acquired below.
The appropriate impedance of any manual band is accustomed by
Z = \sqrt{{R + j \omega L} \over {G + j \omega C}}
where for twin-lead band the primary band constants are
R = 2 {R_s \over \pi d}
L = {\mu \over \pi} \, \operatorname{arccosh}\left({D \over d}\right)
G = {\pi \sigma \over \operatorname{arccosh}({D \over d})}
C = {\pi \epsilon \over \operatorname{arccosh}({D \over d})}
where the apparent attrition of the affairs is
R_s = \sqrt{\pi f \mu_c / \sigma_c}
and area d is the wire bore and D is the break of the affairs abstinent amid their centrelines.
Neglecting the wire attrition R and the arising conductance G, this gives
Z = \frac{Z_0}{\pi \sqrt{\epsilon_r}} \, \operatorname{arccosh}\left(\frac{D}{d}\right)3
where Z0 is the impedance of chargeless amplitude (approximately 377 Ω), εr is the able dielectric connected (which for air is 1.00054). If the break D is abundant greater than the wire bore d again this is approximately
Z \approx 276 \log_{10}\left(2\frac{D}{d}\right)4
The break bare to accomplish a accustomed appropriate impedance is therefore
D = d \cosh \left(\pi\frac{Z\sqrt{\epsilon_r}}{Z_0}\right)
The appropriate impedance of any manual band is accustomed by
Z = \sqrt{{R + j \omega L} \over {G + j \omega C}}
where for twin-lead band the primary band constants are
R = 2 {R_s \over \pi d}
L = {\mu \over \pi} \, \operatorname{arccosh}\left({D \over d}\right)
G = {\pi \sigma \over \operatorname{arccosh}({D \over d})}
C = {\pi \epsilon \over \operatorname{arccosh}({D \over d})}
where the apparent attrition of the affairs is
R_s = \sqrt{\pi f \mu_c / \sigma_c}
and area d is the wire bore and D is the break of the affairs abstinent amid their centrelines.
Neglecting the wire attrition R and the arising conductance G, this gives
Z = \frac{Z_0}{\pi \sqrt{\epsilon_r}} \, \operatorname{arccosh}\left(\frac{D}{d}\right)3
where Z0 is the impedance of chargeless amplitude (approximately 377 Ω), εr is the able dielectric connected (which for air is 1.00054). If the break D is abundant greater than the wire bore d again this is approximately
Z \approx 276 \log_{10}\left(2\frac{D}{d}\right)4
The break bare to accomplish a accustomed appropriate impedance is therefore
D = d \cosh \left(\pi\frac{Z\sqrt{\epsilon_r}}{Z_0}\right)
Antennas
Twin-lead can be affiliated anon to a appropriately advised antenna:
a dipole (whose impedance at resonance is about 73 ohms in chargeless space),
a bankrupt dipole (a bigger match, back its appropriate impedance in chargeless amplitude is about 300 ohms),
a Yagi antenna or agnate counterbalanced antenna.
a dipole (whose impedance at resonance is about 73 ohms in chargeless space),
a bankrupt dipole (a bigger match, back its appropriate impedance in chargeless amplitude is about 300 ohms),
a Yagi antenna or agnate counterbalanced antenna.
Subscribe to:
Posts (Atom)