RF Signal Cables W. Udo Schröder, 2011 Principles Meas/Electronics 2 RG59/U coaxial cable (BNC)...
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Transcript of RF Signal Cables W. Udo Schröder, 2011 Principles Meas/Electronics 2 RG59/U coaxial cable (BNC)...
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RF Signal Cables
W. Udo Schröder, 2011
RG59/U coaxial cable (BNC)Stiffer than RG5875 Ohm impedanceDual shielded cable: copper braid (60%) over foil22 AWG copper covered steel center conductor
Amphenol RG58 coaxial cable (BNC)Impedance 50 OhmBlack PVC cable, tinned copper center conductor & braid for high frequency performanceNickel-plated connector body & Gold-plated center pin contactInsulation: Solid PE (Polyethylene)Rating < 500 VOuter Diameter: 0.195 inches nominalVelocity of Propagation: 66% (50ns/m)
LEMO RG174 coaxial cable (LEMO)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
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Connectors for Coax Signal Cables
W. Udo Schröder, 2011
LEMOLéon Mouttet
Push-pull connectors
BNCBayonet Neill-Concelman
Bayonet mount locking mechanism
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HV Supply Cables
W. Udo Schröder, 2011
MHV connectors:5000 volts DC and 3 amperes. Hazards: HV on exposed central pin, ground disconnects before power. Do not use!
SHV connectors: Do not mate to BNC connectors,Power disconnects before ground.
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W. Udo Schröder, 2011
Signal Transmission Lines
inner conductor
outer conductor/shield
outer conductordielectricmedium
outer casing
Coaxial cables/transmission lines traveling waves in cavity resonators
U UL C
z t
2 2
2 2
Wave equation ideal line
(R0, 1/G 0):
z
L: inductivity C: capacity G: conductance dielectric, depend on diameter and dielectric
Signal propagation speed (speed of light):c-1 5 ns/m
1c LC 0Z L C
Characteristic resistanceZ0=Ohmic resistance!For R≠0, Z0(w) complexImpedance Z0 = 50, 75, 93 W used for timing, spectroscopy,…
U
Elementary replacement circuit for transmission lineper unit length
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Real Cables
W. Udo Schröder, 2011
U
i t kz i t kzz z
For fixed frequency :
C LR G attenuation
L
U
C
k LC wave number
c LC propagation
z ,t U e
speed
e U e e
1 2
12
1
inner outer
Skin Effect :
permeability conductivity
RG C / U :
R Hz . m
R Hz . m
Rr r
5 2
9
58
10 2 4 10
10 2
12 2
4
1 1 Length
20
Traveling waves
Pulse distortion in long cables
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W. Udo Schröder, 2011
Impedance Matching
Rd Rload
Rd Rload
sender receiver
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
0
0
refl load
in load
U R ZU R Z
Polarity of reflected signal Rload=0, ∞
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Pulse Splitting/Adding
W. Udo Schröder, 2011
R1
Uin R2 Uout out outR
U U for slow analog signalsR R
2
1 2
Uin
R
R
R
R
Z0
Z0
Z0
Uout
Uout
Uout
LZ Matched
n Way Splitter
nR Z
n
011
Also use in reverse as 3-way adder
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W. Udo Schröder, 2011
Impedance Mismatch
Receiver input impedance Rload ≠ Z0, use additional Ohmic termination in parallel
Rlo
ad
Rte
rm
L
L
Open end: Rload= ∞ Input and reflection equal polarity, overlap for t > 2Tcable
Tcable = 2L/c
Short: Rload=0, Input and reflection opposite polarity, superposition = bipolar
Multiple (n) reflections attenuated by R-n