. The Bell System technical journal . f 1 /2 inch diameter or less. When it is to beused as an individual cable, the outer conductor is surrounded by a WIDE-BAND TRANSMISSION OVER COAXIAL LINES 661 lead sheath, as shown, to prevent the entrance of moisture. One ormore of the copper tape structures without individual lead sheath may-be placed with balanced pairs inside a common cable sheath. Another flexible structure is shown in Fig. 5. The outer conductorin this case is a lead sheath which directly surrounds the inner conduc-tor with its insulation. Since lead is a poorer conductor than coppe
. The Bell System technical journal . f 1 /2 inch diameter or less. When it is to beused as an individual cable, the outer conductor is surrounded by a WIDE-BAND TRANSMISSION OVER COAXIAL LINES 661 lead sheath, as shown, to prevent the entrance of moisture. One ormore of the copper tape structures without individual lead sheath may-be placed with balanced pairs inside a common cable sheath. Another flexible structure is shown in Fig. 5. The outer conductorin this case is a lead sheath which directly surrounds the inner conduc-tor with its insulation. Since lead is a poorer conductor than copper,it is necessary to use a somewhat larger diameter with this constructionin order to obtain the same transmission efficiency. Lead is also in-ferior to copper in its shielding properties and to obtain the same de-gree of shielding the lead tube of Fig. 5 must be made correspondinglythicker than is necessary for a copper tube. The insulation used in the structure shown in Fig. 5 consists of hard RUBBER WASHER INNER CONDUCTOR (copper). LEAD OUTERCONDUCTOR Fig. 5—Coaxial structure with rubber disc insulators. rubber discs spaced at intervals along the inner wire. Cotton stringor rubber disc insulation may be used with either form of outer hard rubber gives somewhat lower attenuation, particularly at thehigher frequencies. Another simple form of structure employs commercial copper tubinginto which the inner wire with its insulation is pulled. Although thisform does not lend itself readily to a continuous manufacturing process,it may be advantageous in some cases. Transmission CharacteristicsAttenuation At high frequencies the attenuation of the coaxial circuit is givenclosely by the well-known formula: where R, L, C and G are the four so-called primary constants of theline, namely, the resistance, inductance, capacitance and conductance 662 BELL SYSTEM TECHNICAL JOURNAL per unit of length. The first term of (1) represents the losses in theconductors, while the second te
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