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## [TowerTalk] Autek RF-1

 To: [TowerTalk] Autek RF-1 tomwagner@mindspring.com (Tom Wagner) Fri, 16 May 1997 10:32:37 -0400
 ```>From the RF-1 manual: ______________________________________________________________ Determining R + jX As discussed above, R can be determined by canceling X with a series capacitor or inductor. But, R & X can also be calculated directly using SWR & Z measured by the RF1! The formula is: (16) R = ((2500 + Z*Z) * SWR ) / (50 * (SWR*SWR + 1)) where SWR is relative to 50 ohms, as in the RF1 and R is in ohms. (15) X = SQRT(Z*Z - R*R) Then X is determined by equation (15) above. The sign of X is easily determined by increasing the frequency slightly and watching Z. If Z decreases when the frequency increases, then X is negative (capacitive). If Z increases, X is positive (inductive). Use a small frequency change so that Z does not go through a maximum or minimum. The sign of X changes at a max or min Z. (Remember that a feedline can also change the sign of X.) We believe this simple method of determining the sign of X will work in all cases, but there could be a rare exception due to a rapid change in R with frequency... perhaps when R is very large. As a double check, you could connect a small (5 pf?) capacitor in parallel with the load. If Z increases, then X is positive. If it decreases, X is negative. Use the smallest C that shows a measurable Z change. Equation 16 is error-free, and your RF1 is the most accurate SWR and Z measuring device available unless you have a laboratory impedance bridge. However a small error in SWR or Z can cause a large error in R. You can only depend on equation 16 when: a. SWR is greater than 1.2 but less than 6:1, preferable less than 4:1. *and* b. The ratio R/X is not too large or too small. This ratio should be between 0.2 and 5, or the impedance will be dominated by either R or X, and the other will be inaccurate. However, even outside these limits, equation 16 can give sufficiently accurate estimates for many purposes. Just use caution. (This note was first included in RF1 instructions about Sept. 1994. If you know of owners with older instructions, please inform them of this new use for the versatile RF1 that they're probably not aware of.) _________________________________________________________________ I hope this helps. Tom - N1MM >At 08:18 AM 5/16/97 +0100, you wrote: >>According to QST for September 1996, the recent version of the Autek >>instruction manual gives a formula on Page 10 for determining R +/- jX, >>which isn't in my older manual. >> >>Please could somebody let me know the details? >> >>73 from Ian G3SEK Editor, 'The VHF/UHF DX Book' >> 'In Practice' columnist for RadCom (RSGB) >> >>-- >>FAQ on WWW: http://www.contesting.com/towertalkfaq.html >>Submissions: towertalk@contesting.com >>Administrative requests: towertalk-REQUEST@contesting.com >>Problems: owner-towertalk@contesting.com >> > -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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