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## [TowerTalk] Re: [Antennas] coax 'sweet lenght'

 To: antennas@mailman.qth.net,'TowerTalk List' [TowerTalk] Re: [Antennas] coax 'sweet lenght' Bob Nielsen Sun, 10 Oct 2004 12:27:15 -0700
 ```I haven't run any experiments, but I'll concede that some methods of measuring VSWR are less than perfect, in which case that is a definite possibility. Bob, N7XY On Sun, Oct 10, 2004 at 01:50:27PM -0500, Chris Boone wrote: > Ok...what I should have said was "apparent" SWR changes according to the > metering..... > If the cable length changes and the antenna is NOT a resistive only > component, the coax will cause an apparent change in the reactance, thus > making the SWR meter change... > > Any argument with that?? > > Yes, TRUE SWR itself does not change....but the metering is not perfect > :) > > > -----Original Message----- > > From: antennas-bounces@mailman.qth.net > > [mailto:antennas-bounces@mailman.qth.net] On Behalf Of Bob Nielsen > > Sent: Sunday, October 10, 2004 12:12 PM > > To: antennas@mailman.qth.net; 'TowerTalk List' > > Subject: Re: [Antennas] coax 'sweet lenght' > > > > > > WRONG! Ignoring cable losses, the VSWR is independent the > > length of the cable. What changes with length are the > > complex components of the impedance, while the absolute value > > (VSWR) remains constant. > > > > If you plot the impedance on a Smith chart, you get a circle > > whose origin is at the center of the chart where the > > impedance vector rotates as the cable length changes, but the > > length of the vector is constant while the resistive and > > reactive components of the impedance vary. > > > > However, because a matching circuit may not be able to > > compensate for all possible resistance and reactance values > > for a given VSWR (particularly in the case of a very high > > VSWR, such as an end-fed half-wavelength antenna), a > > different cable length may transform the complex components > > of the impedance, as seen at the transmitter, to a value > > which can be more easily matched. > > ______________________________________________________________ > Antennas mailing list > Home: http://mailman.qth.net/mailman/listinfo/antennas > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:Antennas@mailman.qth.net -- Bob Nielsen, N7XY n7xy (at) n7xy.net Bainbridge Island, WA http://www.n7xy.net _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread Re: [TowerTalk] coax 'sweet lenght', (continued) Re: [TowerTalk] coax 'sweet lenght', gdaught6 Re: [TowerTalk] coax 'sweet lenght', Tom Rauch Re: [TowerTalk] coax 'sweet lenght', Pete Smith Re: [TowerTalk] coax 'sweet lenght', corneliuspaul Re: [TowerTalk] coax 'sweet lenght', Don Havlicek Re: [TowerTalk] coax 'sweet lenght', corneliuspaul [TowerTalk] RE: [Antennas] coax 'sweet lenght', Chris Boone [TowerTalk] Re: [Antennas] coax 'sweet lenght', Bob Nielsen Re: [TowerTalk] Re: [Antennas] coax 'sweet lenght', Gene Smar [TowerTalk] RE: [Antennas] coax 'sweet lenght', Chris Boone [TowerTalk] Re: [Antennas] coax 'sweet lenght', Bob Nielsen <= Re: [TowerTalk] RE: [Antennas] coax 'sweet lenght', Tom Rauch RE: [TowerTalk] RE: [Antennas] coax 'sweet lenght', David Robbins K1TTT Re: [TowerTalk] RE: [Antennas] coax 'sweet lenght', Tom Rauch Re: [TowerTalk] RE: [Antennas] coax 'sweet lenght', Tower (K8RI) RE: [TowerTalk] RE: [Antennas] coax 'sweet lenght', Joe Subich, K4IK Re: [TowerTalk] RE: [Antennas] loax 'sweet lenght', Al Williams RE: [TowerTalk] RE: [Antennas] loax 'sweet lenght', David Robbins K1TTT Re: [TowerTalk] RE: [Antennas] loax 'sweet lenght', Tom Rauch