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 /<jim@audiosystemsgroup.com>/* wrote:
>
>
> From: Jim Brown <jim@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
|