by G0KZZ » Fri May 13, 2022 6:28 am
VK5TM wrote: ↑Sat Nov 30, 2019 11:54 pm
I think you need to get rid of one anaylser
(Old Chinese proverb:- Man with two watches not sure what time it is. Translated into hamspeak - Man with too much test equipment mighty confused
).
If the equipment is calibrated correctly there shouldn't be any issues or confusion, if anything it would reinforce the belief in the accuracy of any results obtained.
I have a number of assorted antenna analyzers here, ranging from YouKits ones, MFJ, and Kuranishi, and they will all give pretty much the same indications (within a gnats knacker to use an expression), when connected to the same load to be tested. Same with the minVNA too.
What tends to cause wide variations in readings between units (apart from the obvious calibration differences), is when the person performing the test/s forgets that the outer shield of the coaxial feeder may be 'hot', or in the case of balanced feeder the fact that as soon as it is directly wired to the unbalanced input of an antenna analyzer (pretty well all of the Amateur ones use unbalanced connections e.g. SO239, BNC, N-Type etc.), the 'balanced' feeder has then effectively been grounded on one side, and in the process is no longer balanced.
Keeping the above in mind, you will then get the situation where the analyzer/operator now forms part of the antenna circuit themselves! This can often be detected by noting the readings of an analyzer while being held by the person performing the tests, and then placing the instrument down on some insulated surface and observing any changes. In a lot of cases simply moving your hand near to and then away from the case of an analyzer will cause noticeable changes in SWR and impedance readings, which in turn shows that you are not seeing just the characteristics of the antenna/feeder combo, but also the unwanted stray 'loads'.
Hope that makes sense!
73, Mark...
[quote=VK5TM post_id=1314 time=1575158050 user_id=170]
I think you need to get rid of one anaylser :lol: (Old Chinese proverb:- Man with two watches not sure what time it is. Translated into hamspeak - Man with too much test equipment mighty confused :o ).
[/quote]
If the equipment is calibrated correctly there shouldn't be any issues or confusion, if anything it would reinforce the belief in the accuracy of any results obtained.
I have a number of assorted antenna analyzers here, ranging from YouKits ones, MFJ, and Kuranishi, and they will all give pretty much the same indications (within a gnats knacker to use an expression), when connected to the same load to be tested. Same with the minVNA too.
What tends to cause wide variations in readings between units (apart from the obvious calibration differences), is when the person performing the test/s forgets that the outer shield of the coaxial feeder may be 'hot', or in the case of balanced feeder the fact that as soon as it is directly wired to the unbalanced input of an antenna analyzer (pretty well all of the Amateur ones use unbalanced connections e.g. SO239, BNC, N-Type etc.), the 'balanced' feeder has then effectively been grounded on one side, and in the process is no longer balanced.
Keeping the above in mind, you will then get the situation where the analyzer/operator now forms part of the antenna circuit themselves! This can often be detected by noting the readings of an analyzer while being held by the person performing the tests, and then placing the instrument down on some insulated surface and observing any changes. In a lot of cases simply moving your hand near to and then away from the case of an analyzer will cause noticeable changes in SWR and impedance readings, which in turn shows that you are not seeing just the characteristics of the antenna/feeder combo, but also the unwanted stray 'loads'.
Hope that makes sense!
73, Mark...