3 Spectrum Analyzer Mode
3.7 Burst Power Measurement
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When LNA is installed, the preamp annotation changes to show the state of both
LNA and Internal Preamp. Below is an example:
Note that when operating entirely in the low band (below about 3.6GHz), if LNA is
on, Internal Preamp is switched off (even if you have its switch set to ON). This is
because the noise performance is actually degraded in low band if both preamps are
on. In this case, the annotation reflects the actual state of the two preamps, but the
Internal Preamp annotation displays in amber, to warn you that the actual state of
Internal Preamp does not match its switch control display:
µW Path Control
Options for this control include µW Preselector Bypass (Option MPB), Low Noise
Path (Option LNP) and Full Bypass Enable in the High Band path circuits.
When the µW Preselector is bypassed, flatness is improved, but will be subject to
spurs from out of band interfering signals. When Low Noise Path Enable is selected,
the instrument automatically bypasses certain circuitry in the high frequency bands
that can contribute to noise, when it is appropriate based on other instrument
settings.
For most applications, the preset state is Standard Path, which provides the best
remote-control throughput, minimizes acoustic noise from switching and minimizes
the risk of wear in the hardware switches, particularly in remote test scenarios where
both low band and high band setups will follow in rapid succession. In this path, the
bypass of the low band/high band switch and microwave preamp is never activated,
which can cause some noise degradation but preserves the life of the bypass switch.
For applications that utilize the wideband IF paths, the preset state is µW
Preselector Bypass, if option MPB is present. This is because, when using a
wideband IF such as the 140 MHz IF, the µW Preselector’s bandwidth can be
narrower than the available IF bandwidth, causing degraded amplitude flatness and
phase linearity, so it is desirable to bypass the preselector in the default case.
You may choose Low Noise Path Enable for a lower noise floor, especially in the 21-
26.5GHz region, though without improving many measures of dynamic range, and
1278 Spectrum Analyzer Mode User's &Programmer's Reference
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