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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

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