Detecting Interference Source - Deepace KC901V Manual

KC901V is a VNA, its spectrum test results are for suggestion only.
KC901V's frequency spectrum mode can be interfered by the mirror image. So if
it is used for monitoring, concatenating a narrow-band filter on the input port is sug-
gested. When testing the short-wave frequency spectrum, concatenate a low-pass
filter (e.g. KC9504.02), which the cut-off frequency is 30MHz with suppression over
80dB at 110MHz, and then use it to filter the mirror image interference and IF
feed-though interference. User can also use different Local Mode to identify the mir-
ror image response. If there is IF feed-though interference, concatenate the 110MHz
band rejection primary device (KC9504.03).
If the concerned frequency range is narrow, try to use the narrow-band antenna.
Set CENT and SPAN according to frequency range which needs to be tested. Also set
the AMP according to the strength of the under-the-test signal. When searching the
weak signal, AMP should be set ≤-40dBm. Except it's allowed to have omission, take
the small SPAN to sweep step by step.

4.5 Detecting Interference Source

In the frequency band which has no image interference, user can detect the in-
terference source with KC901V by searching the maximum signal strength direction.
After entering frequency spectrum, set CENT to the frequency which there may
be interference on it and set SPAN to a smaller value (1MHz for example). When the
interference is a bit weak, set AMP as -60dBm. Search the interference signal by ad-
justing antenna's directivity and its polarization mode till there is a maximum bump in
the central of the spectrum. Use the magnetic compass cooperatively to mark the
azimuth angle of antenna's directivity and then draw a direction indication line on the
map. After it, changes another place to do the test again and draws another direction
indication line. These two lines' crossover point is the most probable location of the
potential interference source.
The connecting line of the two testing points should keep the angle between
60-120 °N with another line. It's better that the angle is close 60 °N. (Chart 4-4)
The monitoring location should be as high as possible so that it can avoid the
blockage from the surrounding buildings. When approaching the interference source,
pay attention to adjust AMP according to the signal strength or use the field strength
mode. Then move toward the direction which the interference signal is the strongest
to approach the interference source. Usually, when approaching the interference
source, the tested range should be over 70dBμ（-37dBm）.
putting band pass filters between antenna and instrument can greatly improve
the testing reliability. Usually this filter is in helical structure or in cavity structure. Be-
fore using it, user can adjust its passband frequency under KC901V's monitoring.
When the testing signal is weak, use can also concatenate LNA (low noise amplifier)
between filter and instrument.
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