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Atnenna measurement variations - RF Cafe Forums
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Benny
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Post subject: Atnenna measurement variations
Posted: Sun Sep 25, 2005 1:50 pm
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Hello,
I am doing a range set up using three
antenna systems, I have a 7.5 foot Dish as Source
Antenna and Horn Antenna as Reference , The reading
I get for the same frequency with same set up is
not consistent, I took about 10 reading continuosly
and the range was around 1.5dB difference between
the highest and lowest point, I don't understand
why it could be so inconsistent? Do you have any
idea about it? I would be thankful if you can answer
my question.
Thanks
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Graham |
Post subject:
Posted: Tue Sep 27, 2005 7:08 pm
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Colonel |
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Joined: Fri Sep 02, 2005
7:25 pm Posts: 34 Location: Hampshire UK
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Depending on the frequency in use, you might be
doing pretty good to be able to measure variations
within 1.5 db anyway.
There are lots of variables
here. I take it your source dish is transmitting
a signal generator output horizontally, and you
switch between the horn and your antenna under test
at the other end of the range (is that near, or
some kilometres away)?
The gain lobe in the
source may be high enough that even a slight wind
pressure would be enough. Depending on frequency,
rain or air moisture could affect it. If your antenna
under test is also a dish, you have a double chance
of wobbling the lobes 1.5dB worth. Everything has
to be fixed firmly, and not be prone to vibration.
I was once careless with a piece of heliax coax
cable, and caused more than 1.5dB of problems because
of bending it too hard!
All of the above
assumes you are using very stable calibrated kit.
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Posted 11/12/2012
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