Adjustments for resonance:
https://www.worldwidedx.com/threads/adjustments-for-resonance.257457/page-3#post-761730
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Sirio 2745
- Thread starter twa77
- Start date
Adjustments for resonance:
https://www.worldwidedx.com/threads/adjustments-for-resonance.257457/page-3#post-761730
That’s right where I do most of my talkin. 27.385 and up to around 27.5. If I understand correctly x0 is point of resonance. I just got analyzer if I am just learning the art of fine tuning beyond just simply using swr. I started with Sirios length and was happy where it ended up.
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twa77:
was the analyzer connected directly to the antenna and if not, was the length of the coax used a 1/2 wavelength @ 27.500. here's why i ask.
the only possible swr that could result in R 50 jX 0 (if X is really 0) would be 1:1.
an swr of 1.1:1 (if jX 0) can be the result of only two purely resistive impedances, either 45.45 ohms or 55 ohms. if you use a feedline of any length other than a 1/2 wl. @ 27.500 then the length of the line will change the values of both resistance and reactance that actually exist at the feedpoint of the antenna to some set of values that do not represent the actual values seen at the feedpoint when seen from the analyzer end of the line.
for a 1/2 wl. of feedline such as LMR-400 @ a frequency of 27.500 a length (distance between the analyzer and antenna feedpoint) will be 15.2072 feet or 15' 2.5" or 4.6352 meters in length from plug to plug. this line will allow you to see the exact values of both resistance (radiation resistance + loss resistance) and either capacitive or inductive reactance at the analyzer with the same accuracy as if they were taken directly at the feedpoint without your presence in the induction field of the antenna interfering with the measurements.
see more: https://www.worldwidedx.com/threads/adjustments-for-resonance.257457/page-3#post-761807
was the analyzer connected directly to the antenna and if not, was the length of the coax used a 1/2 wavelength @ 27.500. here's why i ask.
the only possible swr that could result in R 50 jX 0 (if X is really 0) would be 1:1.
an swr of 1.1:1 (if jX 0) can be the result of only two purely resistive impedances, either 45.45 ohms or 55 ohms. if you use a feedline of any length other than a 1/2 wl. @ 27.500 then the length of the line will change the values of both resistance and reactance that actually exist at the feedpoint of the antenna to some set of values that do not represent the actual values seen at the feedpoint when seen from the analyzer end of the line.
for a 1/2 wl. of feedline such as LMR-400 @ a frequency of 27.500 a length (distance between the analyzer and antenna feedpoint) will be 15.2072 feet or 15' 2.5" or 4.6352 meters in length from plug to plug. this line will allow you to see the exact values of both resistance (radiation resistance + loss resistance) and either capacitive or inductive reactance at the analyzer with the same accuracy as if they were taken directly at the feedpoint without your presence in the induction field of the antenna interfering with the measurements.
see more: https://www.worldwidedx.com/threads/adjustments-for-resonance.257457/page-3#post-761807
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well look at that. a line @ 27.500 with a velocity factor of .84% that is 5 1/2 waves long is approximately 75.14 feet. aside of some error within the range of accuracy for the analyzer you're using and being about 1.7 inches short, the reduced capacitance between the vertical element and the radials @ a 45 degree angle compared to the same radials at a right angle to the vertical element is driving the resonance well below 28.6 mhz., in essence electrically lengthening the vertical element below the normal range of resonance for a standard ground plane design. you're in better shape than most here for the first time around.
enjoy!
enjoy!
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