Transmission Lines, Antenna Tuners, and Impedance pptxTransmission Lines, Antenna Tuners ...

69 Pages·2011·1.18 MB·English

Transmission Lines, Antenna
Tuners, and Impedance
MMaattcchhiinngg
3/12/2009 Larry Benko, W0QE 1
Understanding Transmission Lines
• Presentation about antenna tuners and
impedance matching will follow
•• NNeeeedd ttoo uunnddeerrssttaanndd ttrraannssmmiissssiioonn lliinneess ffiirrsstt
• Concepts are interdependent and not separable
• Software simulation is invaluable for better
understanding of the concepts
• Inexpensive test equipment allows measurements
that only a lab could make 10 years ago
3/12/2009 Larry Benko, W0QE 2
Transmission Lines and
Coaxial Cable
• Deliver RF signals to another location efficiently
• Early transmitters did not use transmission lines
• 2/4 wire open wire lines, flexible coax, hard line,
twisted pair, microstrip, wave guide, etc.
• Computer motherboards, Ethernet, USB cables
• Nearly all digital signals are RF these days
3/12/2009 Larry Benko, W0QE 3
Who Can You Believe?
• Too much misinformation and incomplete
information exists
•• TTrraannssiieenntt ccoonnddiittiioonnss aanndd sstteeaaddyy ssttaattee aarree oofftteenn
mixed together which is incorrect
• All concepts presented have been measured in
hardware and simulated in software, often in
multiple programs, with total agreement
• Please challenge me on any topic
3/12/2009 Larry Benko, W0QE 4
Software Tools
(free except EZNec, WinSmith and TLW)
• LTspice IV (previously SwitcherCAD)
– http://www.linear.com/designtools/software/
•• TTLLWW vv33..00 oonn AARRRRLL AAnntteennnnaa HHaannddbbooookk CCDDRROOMM
• WinSmith 2.0
– http://www.scitechpublishing.com
• Collection of Smith Chart stuff
– http://sss-mag.com/smith.html
• SuperSmith
– http://www.tonnesoftware.com/
3/12/2009 Larry Benko, W0QE 5
Software Tools
(free except EZNec, WinSmith and TLW)
• VNA Help SWR Calculator
– http://www.vnahelp.com/products.html
• RFSim99
–– hhttttpp::////wwwwww..pprraaccttiiccaallrrff..ccoomm//$$NNeewwsslleetttteerr//ee--
letters/February2006/RFSim99.htm
• EZNEC
– http://www.eznec.com
– other NEC programs 4NEC2, NEC4Win etc.
• Coax loss & power handling calculator
– http://www.timesmicrowave.com/cgi-bin/calculate.pl
3/12/2009 Larry Benko, W0QE 6
Hardware Tools
• AIM4170B Antenna Analyzer
– http://www.arraysolutions.com/Products/AIM4170B.htm
–– SSeevveerraall ootthheerr ggoooodd aannaallyyzzeerrss aavvaaiillaabbllee
• Time Domain Reflectometer (home brew)
3/12/2009 Larry Benko, W0QE 7
Weaknesses in Software Tools
• LTSpice:
– Transmission line loss constant with frequency
– Q of components is constant with frequency
–– CCaann’’tt mmooddeell ttrraannssmmiissssiioonn lliinnee sshhiieellddiinngg
• TLW:
– Q of components is constant with frequency
• WinSmith:
– Transmission line loss is constant with frequency
• Weaknesses are minimal
3/12/2009 Larry Benko, W0QE 8
How Do Transmission Lines Work?
• At every point along the line the currents in each
wire are the same magnitude and 180 degrees
out of phase
•• FFoorr ccooaaxx,, tthhee ccuurrrreennttss aarree oonn tthhee oouuttssiiddee ooff tthhee
center conductor and the inside of the shield
• AC current flow produces a magnetic field that
opposes current flow
• Transmission line currents produce the minimum
magnetic field which also minimizes radiation
3/12/2009 Larry Benko, W0QE 9
Other Currents on the Line
• A current can flow on both wires equally and is in
phase for open wire line or on the outside of the
sshhiieelldd ffoorr ccooaaxx
• This is an antenna current that does radiate and
is generally unwanted
• Common mode chokes are used to keep this
current at acceptable levels
3/12/2009 Larry Benko, W0QE 10