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Besides image interference, higher-order harmonics, intermodulation and
other reason will also produce false responses, usually below -60dBc. However
in reality, the working conditions of the preamplifier are not ideal, which
probably makes it worse than this value, due to the fact that the total amount
of energy entering the receiver is tremendous. User should note that the front
low-noise amplifier of the KC908 has been working continuously. Manually
turn off the amplification (by press the LEV key, set in the AMP menu) or
setting a higher REF only greatly reduces the gain of the front low-noise
amplifier, but can not 'turn off' it completely. Therefore, the probability of fake
signal is generally greater than traditional spectrum analyzers which the signal
directly inputted into the mixer.
The situation is better than a traditional spectrum analyzer with
preamplifier turnd on. This is a compromise between high sensitivity and anti-
interference ability. For details, see the index of third-order intercept point.
KC908 will generate EMI itself. These radiation will leak into the receiver
from the inside of the instrument, just a small amount.The resulting residual
response is usually below -100dBm. Most part of radiation will leak into the
sky, and those radiation may be received back by its own antenna, especially
when the whip antenna is directly connected to instrument port. This
interference may cause a large residual response.
The residual response mentioned above will be obvious on KC908. One of
the reasons is the instrument will maintain high sensitivity even under a wide
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