Transcript Slide 1
RF Signal Cables Amphenol RG58 coaxial cable (BNC) Impedance 50 Ohm Black PVC cable, tinned copper center conductor & braid for high frequency performance Nickel-plated connector body & Gold-plated center pin contact Insulation: Solid PE (Polyethylene) Rating < 500 V Outer Diameter: 0.195 inches nominal Velocity of Propagation: 66% (50ns/m) Principles Meas/Electronics 2 LEMO RG174 coaxial cable (LEMO) RG59/U coaxial cable (BNC) Stiffer than RG58 75 Ohm impedance Dual shielded cable: copper braid (60%) over foil 22 AWG copper covered steel center conductor W. Udo Schröder, 2011 Impedance 50 ohms Inner Conductor Diameter 0.48 mm Dielectric Diameter 1.52 mm Shield Diameter 2.23 mm Capacitance 100.0 pF/meter (30.5 pF/foot) Minimum Operating Temperature -40 C (-40.0 F) Maximum Operating Temperature 75 C (167.0 F) Jacket Diameter 2.79 mm Jacket Material PVC Velocity Ratio 66% Core stranded Connectors for Coax Signal Cables Principles Meas/Electronics 3 BNC Bayonet Neill-Concelman W. Udo Schröder, 2011 Bayonet mount locking mechanism LEMO Léon Mouttet Push-pull connectors Principles Meas/Electronics 4 HV Supply Cables MHV connectors: 5000 volts DC and 3 amperes. Hazards: HV on exposed central pin, ground disconnects before power. Do not use! W. Udo Schröder, 2011 SHV connectors: Do not mate to BNC connectors, Power disconnects before ground. Signal Transmission Lines outer casing outer conductor/shield inner conductor dielectric medium z outer conductor 5 Coaxial cables/transmission lines traveling waves in cavity resonators Elementary replacement circuit for transmission line per unit length Principles Meas/Electronics U L: inductivity C: capacity G: conductance dielectric, depend on diameter and dielectric Wave equation ideal line (R0, 1/G 0): 2 2 U U L C z 2 t 2 c 1 LC Z0 L C W. Udo Schröder, 2011 Characteristic resistance Z0=Ohmic resistance! For R≠0, Z0(w) complex Impedance Z0 = 50, 75, 93 W used for timing, spectroscopy,… Signal propagation speed (speed of light): c-1 5 ns/m Real Cables U For fixed frequency : i t kz i t kz U z ,t U1 e z e U2 e z e Principles Meas/Electronics 6 1 C L R G attenuation 2 L C k LC wave number c 1 propagation speed LC Traveling waves Pulse distortion in long cables Skin Effect : permeability conductivity R 1 2 2 1 1 rinner router RG 58 C / U : R 10 Hz R 105 Hz 2.4 102 W m 9 2.4 W m W. Udo Schröder, 2011 0 Length 2 Impedance Matching Rd receiver sender 7 Rload Principles Meas/Electronics Rd W. Udo Schröder, 2011 Rload For impedance matching, Rload=Z0, cable looks infinitely long: no reflections from end. For mismatch, Rload ≠ Z0, reflection at end, traveling back, superimpose on signal Urefl Rload Z0 Uin Rload Z0 Polarity of reflected signal Rload=0, ∞ Pulse Splitting/Adding R1 Uin Uout R2 U R1 R2 out for slow ana log signals 8 R2 Uout Principles Meas/Electronics R R Uin W. Udo Schröder, 2011 R R Uout Uout Uout Z0 Z0 Z0 ZL Matched n Way Splitter R n 1 Z0 n 1 Also use in reverse as 3-way adder Principles Meas/Electronics 9 L Rterm Rload Impedance Mismatch Receiver input impedance Rload ≠ Z0, use additional Ohmic termination in parallel Open end: Rload= ∞ Input and reflection equal polarity, overlap for t > 2Tcable Tcable = 2L/c L W. Udo Schröder, 2011 Short: Rload=0, Input and reflection opposite polarity, superposition = bipolar Multiple (n) reflections attenuated by R-n W. Udo Schröder, 2011 Principles Meas/Electronics 10