Hi Jim, Yes, the variation with frequency that you saw was the transmission line behavior. I'd say that the 1 MHz numbers are good.
73, Jim K9YC On 2/10/2012 5:43 AM, Jim F. wrote: > Hi Jim, > Thank you so much for the reply. Here is what I did. > I tried an Autek RF-1 antenna analyzer to measure the 72 foot 2 > conductor cable > installed in my basement but the capacitance varied widely with frequency. > I then went to an LC measuring circuit built from the Winter of 1993 > Communications Quarterly that has an Oscillator running at 1.017 > mHz and used it to determine the cable (capacitance per foot) in my > basement as a reference. (24'/pf) > Is 1/20 wavelength of 1.017 mHz = ~ 215' ignoring Vp ? > I estimate that the cable going to the condo furthest away could be > over 100' and it measured a calculated 125'. > Do you think that is reasonable ? > Thanks again, > Jim / W1FMR > > --- On *Thu, 2/9/12, Jim Brown /<j...@audiosystemsgroup.com>/* wrote: > > > From: Jim Brown <j...@audiosystemsgroup.com> > Subject: Re: Topband: 4 new radials... > To: topband@contesting.com > Date: Thursday, February 9, 2012, 11:22 PM > > On 2/9/2012 6:12 PM, Jim F. wrote: > > Using measured capacitance between the two conductors > > of my cable ( 24pf / ft.) it was easy to calculate the lengths of > > cables going to the other 3 condos. > > At what frequency did you make that capacitance measurement, and > how did > you make it? When the frequency is high enough that the cable you > are > measuring is longer than about 1/20 wavelength (taking Vp into > account), > the behavior of the cable as a transmission line will cause > measurement > error. > > 73, Jim K9YC > _______________________________________________ > UR RST IS ... ... ..9 QSB QSB - hw? BK > > No virus found in this message. > Checked by AVG - www.avg.com <http://www.avg.com> > Version: 2012.0.1913 / Virus Database: 2112/4799 - Release Date: 02/09/12 > _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK