Detecting Interference Source - Deepace KC901M User Manual

The determined maximum limiting power input level is for sake of keeping the
instrument safe only. It doesn't guarantee the testing accuracy at this level. To obtain
more precise results, the input level should less than +13 dBm.
KC901M is an VNA, its spectrum function is only for reference use.
KC901M'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
suggested. 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
mirror image response. If there is IF feed-though interference, concatenate the
110MHz trap filter (KC9504.03).
There may occur a confusing peak of interference by another mirror which is
approximately 40dB lower than the main peak. It can be told from switching between
High LO and Low LO.
Better use the narrow-band antenna when the chosen frequency range is narrow. Set
CENT and SPAN according to the frequency range which needs to be tested. Also set
the AMP accordingly to the strength of the under-the-test signal. When searching the
weak signal, AMP should be set ≤-40dBm. Adopt smaller SPAN for more meticulous
sweep.

4.5 Detecting Interference Source

In the frequency band which has no image interference, user can detect the
interference source with KC901M by searching the maximum signal strength
direction.
After entering the frequency spectrum, set CENT to the frequency which may be
interfered and SPAN to a smaller value (1MHz for example). When the interference is
feeble, set AMP as -60dBm. Search the interference signal by adjusting antenna's
directivity and its polarization mode till there appears a maximum bump in the central
of the spectrum. Use the magnetic compass to mark the azimuth angle of antenna's
directivity and then draw a direction indication line on the map. Next, find another
place to do the test again and draws another direction indication line. The crossover
point of these two lines is the most probable location of the potential interference
source.
The line formed by the two testing points should cross with either one direction
line (mentioned above) at an angle between 60-120 °N, better close to 60 °N. (Chart
4-4)
The monitoring location should better be high and capacious enough to avoid
obstructive objects (such as buildings). Approaching the interference source, adjust
AMP according to the signal strength or use the field strength mode. Move towards
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