So to plug some numbers in: Say you have a cable with the following specs (50 ohm cable) Capacitance of 100.3 pF/m Inducatance of 251 nH/m Resistane of 0.164 ohms/m Shunt conductance of 12.8 mS/m
Zo = sqrt [ (R + j 2 pi f L ) / (G + j 2 pi f C ) ] at 100 Hz= 113 ohms at 1 Khz= 111 ohms at 10 Khz= 97 ohms at 100 Khz= 65 ohms at 1 Mhz= 52 ohms at 100 Mhz= 50 ohms at 1 Ghz= 50 ohms Proved.com Jesse On 9/2/07, Ron Wright <[EMAIL PROTECTED]> wrote: > > Jeff, > > I have plenty of text books here, oh well. All refer to impedance as Z and > Z=R+jX or Z = magnitude and phase angle. A 500 Ohm resistor has an impedance > of 500 Ohms or 500+j0 or 500 0 deg phase. > > I think in Jesse's and my last posting you might see about the low and > high freq differences in coax. Maybe not. > > Oh well. Good discussion. > > 73, ron, n9ee/r > > >From: Jeff DePolo <[EMAIL PROTECTED] <jeff%40depolo.net>> > >Date: 2007/09/02 Sun PM 12:12:51 CDT > >To: [email protected] <Repeater-Builder%40yahoogroups.com> > >Subject: RE: RE: RE: RE: RE: RE: RE: Re: Re: RE: [Repeater-Builder] Re: > Duplexers > > > > >> Impedance refers to both R and X, resistance and reactance. Impedance > >affects all current flow, DC and AC. X affects AC only. > > > >Impedance is specific to AC. There's no such thing as impedance at DC, > only > >resistance. Look up in the definition of impedance in any engineering > text > >and you'll find that it only applies to AC. > > > >A cable's characteristic impedance is determined by the ratio of E to I > when > >there are no reflections on the line. Reflections can only exist when the > >current being carried is varying, i.e. an AC waveform. > > > >A coaxial cable that has a 75 ohm characteristic impedance will conduct > >steady-state DC at any E to I ratio, and will do so without reflection. > The > >cable does not perform any transformation regardless of the load, unlike > the > >AC case. > > > >> No a coax will not function the same at 5 Hz as it does at 2 meters. > > > >Why not? > > > >> Evidently you have not had the previledge of working with > >> equipment or engineers that allows one to look at some of > >> these issues. > > > >Oh, I think have... > > --- Jeff > > > > > > Ron Wright, N9EE > 727-376-6575 > MICRO COMPUTER CONCEPTS > Owner 146.64 repeater Tampa Bay, FL > No tone, all are welcome. > > >
