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#18
August 24th 09, 04:45 PM
posted to rec.radio.amateur.antenna
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MFJ-269 Antenna Analyzer experience
Michael Coslo wrote:
wrote: The 4170 makes this a lot easier as you can measure the feedline actual parameters as well as calibrate out their effects. This is a dumb question on my part, but what you are saying is that the mitigating effects that the cable has on the VSWR, making it look better in general, can not only be calculated and "calibrated out", but that the actual SWR of your antenna at the feedpoint is then given? As you get closer to 1.1:1 at the actual antenna, would accuracy then suffer? If feedline loss can bring an antenna that is not near that to a level approaching that, wouldn't it mean that teh calibration is somewhere in the noise? Like I say, this could be a really stoopid question. - 73 de Mike N3LI - Basically what you do is calibrate the instrument at the measurement point, whether that point is the instrument connector or at the end of a length of coax. You attach an open, a short and a known resistance; 50 ohms by default but it is user definable. The instrument than frequency sweeps and stores the results in a user definable calibration file. When you make a measurement of an unknown, you define which calibration file to use and the instrument corrects the readings to display the characteristics at the measurement point. Given that this is a $500 insturment and not a $20,000 labratory instrument there are going to be limits to how accurate all this is. After having used the AIM for a while, my opinion is that it far execeeds what is required for practical amateur usage. If you want to see some actual numbers, you can find a comparison of the results of an AIM 4170 compared to HP lab equiment at: http://www.bnk.com/w0qe/AIM4170_page1.html -- Jim Pennino Remove .spam.sux to reply. |
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