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Post by thadde on Jan 27, 2012 10:58:30 GMT -5
Hallo everybody
I measured Zo of a RG58 coaxcable with the 4170C. A short cable (1m) gave a result of 55 Ohm and a long one (7m) gave a result of 52 Ohm. The impedance of such cable is 50 Ohm. Zo is the result of L/C root square. Why is a measured Zo not 50 Ohm? Is there a tolerance or is there an unknown factor? I would like to measure feedlines (symetric) and would be happy about excact impedance.
Who has me an answer? My best 73 de Thadde HB9DNB Switzerland
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Post by Bob on Jan 28, 2012 15:07:05 GMT -5
RG58 coax has a wide range of impedance values. Typically it is around 51 to 53.5 ohms. For example, the table included with Transmission Lines Details shows values of 50, 51.5, 52, 53.5 for RG58 style cables. The impedance is also a function of frequency. The AIM measures the impedance at the frequency corresponding to one-eight of a wavelength for the cable under test. Dan has a lot of information about this: www.ac6la.com -- 73/Bob |
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Post by thadde on Feb 3, 2012 10:52:23 GMT -5
Dr om Bob
Mni tnx for good answer. It is clear now for me, that the specification of a RG58 is not accurate 50 ohms. How ever I would like to measure a symetric feed line and I ask: can I trust the result (Zo) of the AIM 4170? I can calculate a such feed line with formulas. Dialectricum would be air.
I wish you a good weekend, here it is vy cold, so I stay indoors, hi.
Best 73 and mni tnx de Thadde HB9DNB Lucerne, Switzerland
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Post by Bob on Feb 3, 2012 13:28:21 GMT -5
You may get better results by using a balun at the output of the AIM. Put the calibration loads on the output of the balun. Then connect the feed line to the balun and measure it. Be sure to keep the line several wire spacings from any metal object or the ground.
To see if the Zo is reasonable, put a resistor at the far end of the line and look at the SWR.
--73/Bob
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Post by greenorange on Feb 21, 2012 1:14:16 GMT -5
This post has been somewhat of a revelation to me.
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