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TRANSMISSION LINES. Chuck G0MDK. MYSTERY GUEST. Does any one recognize this Gentleman?. TRANSMISSION LINE TYPES. TWISTED PAIR TRANSMISSION LINE. Characteristic impedance 100 – 125 ohms Used primarily in telephone circuits It was never intended for RF use
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TRANSMISSION LINES Chuck G0MDK
MYSTERY GUEST Does any one recognize this Gentleman?
TWISTED PAIR TRANSMISSION LINE Characteristic impedance 100 – 125 ohms Used primarily in telephone circuits It was never intended for RF use Invented by Alexander Graham Bell Reduced cross talk and interference from trams Balanced lines main advantage High attenuation at RF frequencies
TWO WIRE TRANSMISSION LINES Prices per metre 300 Ohm ribbon £0.80 300 Ohm slotted ribbon £1.00 450 Ohm ladder line £1.20
TWO WIRE TRANSMISSION LINES Some calculations for characteristic impedance d and r values can be any units like inches, millimetres, furlongs etc. but the units for d and r must be the same Example: d = 100mm and r = 0.5mm: Z0 = 635 ohms Double wire size to 1mm radius: Z0 = 552 ohms Half the spacing to 50mm: Z0 = 469 ohms
TWO WIRE LADDER LINE HOME BREW Attenuation of home brew ladder line: 14 AWG wires spaced 12.2cm = 600 ohms Nylon spacers Attenuation of 30MHz over 100 feet = 0.06dB Attenuation of 100 feet of RG-58A/U = 2dB Notes: #14 AWG = 1.62mm diameter 19 strands PVC insulated covering suggested
COAXIAL CABLE Evolution of the Coaxial Cable: 1880 Oliver Heaviside patented coaxial cable in England. He also developed the first theory on transmission lines 1884 Siemans patented coaxial cable in Germany 1929 first modern coaxial cable patented by Lloyd Espenschied and Herman A. Affel & assigned to the American Telephone & Telegraph Co. It was needed to reduce cross talk between signal cables 1935 Polyethylene invented in US. 1956 Transatlantic coaxial cable laid
OLIVER HEAVISIDE Who was Oliver Heaviside? English Mathematician and Engineer 1850 - 1925 Had scarlet fever which left him nearly deaf. Left school at 16 Was 5th in a class of 500 Self taught Danish and German. Learned Morse Code at 18 Became Telegrapher in Denmark and then Newcastle At 21 published paper on Electricity and a 2nd one a year later Maxwell published results in “Treatise on Electricity and Magnetism 2nd edition. Heaviside studied this edition being determined o understand it Studied Maxwell’s 20 equations Developed Vector Calculus. Reduced Maxwell’s 20 equations with 20 variables to 4 which we all see today. Elected fellow to the Royal Society in 1891
OLIVER HEAVISIDE Maxwell’s Equations U0 = Permeability of free space = 4π×10−7 Henrys per metre e0 = Permittivity of free space = 8.85 x 10-12 Farads per metre • Gauss’ Law for electricity. e0 permittivity of free space • Gauss’ Law for magnetism • Faraday’s Law for induction • Ampere’s Law. uo permeability of free space
COAXIAL CABLE dB loss per 100 feet * LDF is 0.5” Andrews Heliax Power handling (Watts)
VELOCITY FACTOR How fast does a signal travel through space? 300 million m/s or ~ 1’/ns Actually 0.984 feet per nanosecond How fast does the signal travel through coaxial cable? It depends on the cable dielectric material If the material is just air, signals will travel ~ light speed (c) For other materials the signal will be slower than light. Air has a dielectric constant of 1.00054 Other materials are greater Polyethylene dielectric constant is 2.29 Using formula: VF = 0.66 or 2/3 c RG-58 & RG-213 VF = 0.66
COAXIAL CABLE Calculating Coaxial cable impedance It depends on the cable dielectric material, and the shield and inner conductor dimensions e = dielectric constant D = Shield diameter d = inner conductor diameter
ANTENNA TRANSMISSION LINE SYSTEM-1 Dipole cut to desired frequency. Balun and centre fed 50’ feeder (~ 15m) has < 0.5dB attenuation VSWR normally < 3:1 Rig ATU deals easily with it. The power reflected at 3:1 is ~30%
ANTENNA TRANSMISSION LINE SYSTEM-2 450 ohm ladder line grossly mismatched to Ant. and Tx Special condition where a match will occur without the ATU When transmission line is multiple ½ wavelengths long Other lengths ATU must be used to get a match It appears that the ATU effectively shrinks or stretches the transmission line to get multiple ½ wavelengths
WAVEGUIDE Wave guide manufacturers are the blacksmiths of the microwave industry Visit a wave guide house and you will see a bunch of old bearded guys with hammers, files, grinding wheels, and welders, getting it done. They all will have gone to University
WAVEGUIDE-1 What is a wave guide? Metallic transmission line used at microwave frequencies. Like coax cables it interconnects transmitters, receivers and antennas. Here’s an example: Rectangular pipe most commonly used Circular types are less common. Made of copper or aluminium. The inside surface silver plated for low loss. Advantages:Highly shielded, Manage high peak power Extremely low losses Disadvantages: High cost Manufacturing volumes low and unwieldy at low u-wave frequencies due to size.
WAVEGUIDE-2 Wave guide TE 10 mode Wave guide end view showing Electric field In this case the wave guide width is exactly ½ wave length If we lower the frequency the wave length will become correspondingly longer The wave guide won’t accommodate the longer ½ wave As such, the lower frequencies will be cut off Increasing the frequencies result in shorter wave lengths. These are easily accomodated and the signals will pass.
WAVEGUIDE-3 Some waveguide components
WAVEGUIDE-4 WR-90 x-band waveguide (loss): Dimensions 2.3cm x 1.02cm 0.5 wave length 6.0GHz = 2.5cm 7.0GHz = 2.0cm 8.0GHz = 1.9cm 10GHz = 1.5cm 12GHz = 1.25cm Notice the sharp cut-off below ~ 7GHz
WAVEGUIDE-5 More on Wave guide loss WR-90: 0.108 dB/m (10 GHz), WR-62: 0.168 dB/m (15 GHz)WF-42: 0.370 dB/m (21 GHz)WR-28: 0.576 dB/m (32 GHz)WR-19: 1.04 dB/m (48 GHz)WR-15: 1.51 dB/m (60 GHz)WR-12: 1.97 dB/m (75 GHz)WR-10 2.69 dB/m (90 GHz) Notes: The rectangular wave guides aspect ratio is ~ 2 : 1 The WR # indicates wave guide dimensions in inches. For example: The wide dimension of RG-90 is 0.9”, WR-62 is 0.62”, etc.
