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Total posts : 45366Below is clip from the IEEE paper NBS Field-Strength Standards and Measurements showing how the height above the earth of a 1/2-wave dipole antenna affects the field intensity it receives.
This shows the importance when making accurate field intensity measurements of using the receive antenna at the height above ground at which its antenna factor was measured.
Measuring error increases rapidly for changes in antenna height, for low elevations above the earth.
(The complete IEEE paper is available at http://tinyurl.com/gne9vbv)
Total posts : 45366I wish I had the mindset better capable of really understanding such post.
Total posts : 45366
Total posts : 45366The graphic linked in Reply 4 above states that the antenna used to measure field intensity should be “height-scanned over 1-4 metres to find the maximum emissions … for both horizontal and vertical polarisations.”
However if such measurements are accurately to be made, that requires knowledge of the antenna factor (AF) of that receive antenna at the test frequency across that 1-4 meter “height scan,” for both vertical and horizontal polarization of that receive antenna. Otherwise those measurements will NOT be accurate.
Does anything in EN 55022 recognize this, and address it?
Total posts : 45366If you’re simply taking field intensity to determine if a transmitter is legal such scanning would most likely not be necessary.
e.g. I do my tests at 7 feet simply because this is one of the two heights documented in the FIM-71 manual and antenna factors are supplied. so, when I take a reading and find the transmitter to be many multiples above the lega limit there’s really no need to determine where the maximum FI might be, as it’s already been determined to be over the limit.
However, testing for compliance in a lab this information would be needed, as certification would require all emissions at any height to be under the limit.
TIB
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The NIST has a good paper on the complexities of this topic. See
https://www.nist.gov/document-14711
Below is a clip from that paper describing how a calibrated receive antenna can be used with an r-f spectrum analyzer for measurement of electric field intensity.
Note that the Antenna Factor of the receive antenna accurately must be known.
The only way to determine that is for it to be tested/characterized using those physical and electrical conditions when “immersed” in an accurately known radiated field, for those conditions.