ExpStep = (Log(LastFreq) - Log(FirstFreq)) / (NumSteps - 1)Once you've picked a value for 'FirstFreq' the subsequent frequencies can be calculated as follows.2nd Freq = 10 ^ (Log(FirstFreq) + 1 * ExpStep)
Nth Freq = 10 ^ (Log(FirstFreq) + (N-1) * (Log(LastFreq) - Log(FirstFreq)) / (NumSteps - 1))So let's apply this to the frequency steps on the Calculate sheet, with the assumption that the first frequency will be 1 MHz, the last frequency will be 100 MHz, and the number of frequency steps will be 25. Open, what else, BYDIPOLE.ez. On the Wires sheet use the AutoSeg button to assign 40 segments per wavelength, odd. That way as the frequency changes over the full range from 1 to 100 MHz the single wire of the model will always have the same segmentation density although a different number of segments for each test case.
= ROUND(10 ^ (LOG(B$11) + (ROW()-11) * (LOG(LastFreq) - LOG(B$11)) / (NumSteps - 1)), 3)Hint: You can swipe the above line on this web page, press Ctrl-C to copy, return to the Excel window, select cell B12, click on the formula bar to activate it (or just press F2), then press Ctrl-V to paste. (If you neglect to click on the formula bar or press F2 you will paste both the text characters and the text font, not what you want.) Change 'LastFreq' to 100 and 'NumSteps' to 25, then press Enter.If you press Enter before changing 'LastFreq' and 'NumSteps' the formula will evaluate to the Excel error code '#NAME?' meaning you used an undefined name in the formula. That's not a catastrophe, just revise the formula to replace the undefined names 'LastFreq' and 'NumSteps' with the desired numeric values of 100 and 25.
(Press Esc to stop the animation, F5 to restart.)
=INDEX(LINEST(B2:B22, A2:A22^{1,2}), 1, 1)Note that the '{1,2}' portion is in braces, not parenthesis.The formulas will evaluate to:
=INDEX(LINEST(B2:B22, A2:A22^{1,2}), 1, 2)
=INDEX(LINEST(B2:B22, A2:A22^{1,2}), 1, 3)
The most accurate way to make antenna measurements is to temporarily disconnect the far end of the transmission line from the antenna, place OSL (Open-Short-Load) terminations at the far end, connect the shack end of the line to your instrument, and perform a calibration. This will move the reference plane of your instrument to the antenna feedpoint, effectively 'calibrating out' the transmission line. Then reconnect the feedline to the antenna and make measurements over the frequency range of interest. Readings you make at the shack end of the line will then be the same as if you had made them directly at the antenna.