Hi Brent, I had the same problem when I designed mine. By using square stock, which is great for building a log-p, I was not able to get the impedance necessary to make it look 50 ohms at the driving end(but close enough to keep the VSWR < 2:1). I was also trying to push the limits on gain and size. In any event, I finally wound up measuring the characteristic Z of the square stock transmission line. At close spacing the formula is Zo=377(w/l) for l/w>10. w is the spacing and l is the thickness of the rod. If l/w is <0.1 then use Zo=120*cosh-1(w/l) or Zo=276*log(2w/l). If you are in the area of w=l then use Zo=sqrt(L/C) where L is the inductance per unit length and C is the capacitance per unit length. Measure these on your HP impedance or network analyzer. This gets you very close. Good luck! Give me a call if you would like more info.
Best Regards, Jim Jim Conrad Conrad EMC Consulting P.O. Box 25 Hamilton, MA 01936 U.S.A. E-mail: jc...@shore.net Phone: 978-468-3909 FAX: 978-468-1034 -----Original Message----- From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org]On Behalf Of brent.dew...@us.datex-ohmeda.com Sent: Wednesday, August 28, 2002 6:26 PM To: emc-p...@majordomo.ieee.org Subject: Transmission line formula? Anyone have a formula for calculating the Z0 of two parallel rectangular pieces of metal tubing in air? I'm designing a log-periodic antenna and need to get the boom transmission line spacing right. Thanks! Brent DeWitt Datex-Ohmeda ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
