
April 4th 08, 05:40 AM
posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Dec 2007
Posts: 95
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The Rest of the Story
On Thu, 3 Apr 2008 17:50:05 -0700 (PDT)
Keith Dysart wrote:
On Apr 3, 6:47*pm, Roger Sparks wrote:
On Thu, 3 Apr 2008 10:35:17 -0700 (PDT)
Keith Dysart wrote:
On Apr 3, 9:47*am, Roger Sparks wrote:
On Wed, 2 Apr 2008 06:33:46 -0700 (PDT)
I am sorry Keith, but I still can not duplicate your work. *I wonder if the difference is in how we each apply the recharge voltage to the transmission line.
I do not know. The spreadsheet that did the work is now available from
this page:
http://keith.dysart.googlepages.com/radio6
Perhaps with the extra detail, you can find the discrepancy.
I redid my table showing the *power in the source and reflected waves. *I now have the power to resistor Rs coming from voltage agreeing with the expected power calculated from current. *
My sheet agrees with yours for the samples I checked.
...Keith
I think that at 91 degrees, the sign of the returning wave should be positive, not negative. *Thus, it should be +1.234v. *My reasoning is that the voltage from the line side of the resistor adds to the voltage from the source side of the resistor, *but in this case it takes a little longer to get around the loop. *The 90 degrees is timing, the lead edge of the wave is not reversed by turning the corner at what we call the short. *
I do believe that -1.234 is correct. The reflection coefficient is -1,
so at the
short, Vr(t) is always equal to -Vf(t), which, when summed, give a
Vtot(t) of 0
which is what is expected at a short. Vr.g(t) is delayed by 90 degrees
from
Vf.g(t) so at 91 degrees, we should expect Vr.g(91) to be (-1 *
Vf.g(1)) or
-1.234. This is also how the spreadsheet computes it.
OK, I see now. You reversed the sign to calculate Vrs so once I get to the Vrs column, we are the same. You used the -1 reversal to calculate Vg, but plus one to calculate Vrs.
clip
On this sheet, Vtot = Vf+Vr, Itot=If+Ir and Ptot=Pf+Pr.
I hope no gremlins snuck in.
...Keith
I will go back and look some more at the power relationships from your earlier posting.
--
73, Roger, W7WKB
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