AE6PM 11/06/20071 Heard at Pacificon Technical tidbits from selected presentations

AE6PM 11/06/20072 Steve Stearns, K6OIK Pacificon 2001 Coaxial cable characteristic impedance Z o = 50Ω has no special significance For minimum lossZ o = 77Ω For maximum breakdown voltage Z o = 30Ω For minimum temperature rise Z o = 60Ω

AE6PM 11/06/20073 Steve Stearns, K6OIK Pacificon 2001 Round Open-Wire Transmission Line Impedance Formulas: Approximate, widely published, but accurate only for large spacings: s/d>3. Z 0 = 120 ln(2s/d) = 276 log 10 (2s/d) Exact, accurate for all spacings & impedances Z 0 = cosh -1 (s/d)

AE6PM 11/06/20074 Comment Yet another equation: Z 0 = 276 log 10 (s/d+ sqrt((s/d) 2 – 1) d = conductor diameter S = center-to-center spacing

AE6PM 11/06/20075 Steve Stearns, K6OIK Pacificon /2λ transmission line repeats the impedance of the load Z i = Z L 1/4λ transmission line repeats the reciprocal of the load Z Z i = Z o 2 /Z L

AE6PM 11/06/20076 Steve Stearns, K6OIK Pacificon /8λ transmission line always shows the impedance of the transmission line X L = Z o tan l for a short-circuited line less than 1/8λ in length ( l) 1/8λ = 45 o and tan 45 o = 1 The impedance at the antenna is almost never what is seen at the input end of the transmission line. - AE6PM -

AE6PM 11/06/20077 Steve Stearns, K6OIK Pacificon 2004/2005 For an exact half-wave dipole, l = λ/2: Z A = j41.52 Independent of wire diameter For a resonant dipole, l < λ/2: Z A = j0 Depends on wire diameter Resonance is just an impedance property Maximum gain for a dipole is 5.18 dbi at a length of 1.269λ

AE6PM 11/06/20078 Steve Stearns, K6OIK Pacificon 2006 QEX Sep/Oct 2001 is not the way to match. Forget conjugate match (which assures maximum power transfer). The important thing is to prevent reflections (which cause waveform distortion and degrade information transfer).

AE6PM 11/06/20079 Comment The QEX article in question is evidently: “A Flat Impedance Bandwidth for any Antenna” by Grant Bingeman, KM5KG

AE6PM 11/06/ Comment So which is the best? –Conjugate match (Maxwell) Maximum power transfer –Maximum SWR bandwidth (Bingeman) Maximum operating convenience –Minimum waveform distortion (Stearns) Maximum fidelity for digital modes

AE6PM 11/06/ Steve Stearns, K6OIK Pacificon 2006 A Dipole antenna differentiates the signal once A Loop antenna differentiates the signal twice Digital TV will require a discone antenna or a bow tie antenna or a ?

AE6PM 11/06/ Comment Conversation with Steve Stearn 10/19/07: –Yagi and log periodic antennas introduce phase distortion. –Bow tie and discone antennas do not introduce phase distortion. –Most digital modes are intolerant of signal distortion.

AE6PM 11/06/ Tom Schiller, N6BT Pacificon 2006 Round elements are more efficient than square or rectangular. Solid wire for radials is more efficient than stranded. Stainless steel is a very poor conductor (high resistivity). Galvanized wire is a very poor conductor (coating too thin: skin effect).

AE6PM 11/06/ Tom Schiller, N6BT Pacificon 2006 Maybe 12 dB improvement by silver plating stainless steel. Copper clad, not copper coated or copper plated (again, due to skin effect).

AE6PM 11/06/ Comment  =  (2  /  ) Where:  = skin depth  = resistivity of conductor  = angular frequency of current  = absolute magnetic permeability of conductor 1 MHz = 2.84 mils 10 MHz = mils 30 MHz = mils Zinc = ? Steel = ? Aluminum = ?

AE6PM 11/06/ Steve Stearns, K6OIK Pacificon 2007 RL db = -20 log |  | Errors correcting errors …. stuff happens: Return Loss in decibels is 20 times the logarithm of the Reflection Coefficient –WorldRadio, January 2007 p52 (wrong) Return Loss in decibels is 20 times the logarithm of the Voltage Reflection Coefficient –Correction in WorldRadio, March 2007 p52 (wrong) Return Loss is 20 times the reciprocal of the Reflection Coefficient –Correction in WorldRadio, June 2007 p52 (wrong)

AE6PM 11/06/ Comment Errors correcting errors …. The correct answer is: RL db = -20 log |  | Where  = reflection coefficient = E r /E f = I r /I f Ref: The ARRL Antenna Book, 21 st Edition, p24-8

AE6PM 11/06/ Articles by Steve Stearns “Mysteries of the Smith Chart: Transmission Lines, Impedance Matching, and Little Known Facts” “Antenna Impedance Models – Old and New” “New Results on Antenna Impedance Models and Matching”

AE6PM 11/06/ Articles by Jim Brown, K9YC “Understanding and Eliminating RF Interference” “Transmitting Chokes” “RFI, Ferrites, and Common Mode Chokes for Hams” “Measured Data For HF Ferrite Chokes” ….. and many more

AE6PM 11/06/ K6OIK’s Broadband Equivalent Circuit 98.4’ 5 MHz, thin wire dipole resonant at 4.8 MHz. See Pacificon presentation chart for component values.

AE6PM 11/06/ Accuracy of K6OIK’s Broadband Equivalent Circuit