3 Short-Range Comms & IoT Mode
3.4 HRP UWB Demodulation Measurement
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
without giving the best possible noise floor. The preamp, if purchased and used,
gives better noise floor than does Low Noise Path Enable, but the preamp’s
compression threshold and third-order intercept are much poorer than that of Low
Noise Path Enable.
A fourth choice is Full Bypass Enable, which combines µW Preselector Bypass and
Low Noise Path Enable. Because this can bypass most of the circuitry between the
input and the first mixer, care should be taken when using this setting to avoid
damaging the mixer. Full Bypass Enable is only available if both options LNP and
MPB are present, as well as option FBP.
Path Example Note
Standard Path :POW:MW:PATH
STD
Normal setting for most measurements. µW Preselector
in circuit, Low Noise Path disabled
Low Noise Path
Enable
:POW:MW:PATH
LNP
See "Low Noise Path Enable" on page 469
µW Preselector
Bypass
:POW:MW:PATH
MPB
See "µW Preselector Bypass" on page 471
Full Bypass
Enable
:POW:MW:PATH
FULL
See "Full Bypass Enable" on page 472
Short Range Comms & IoT Mode User's &Programmer's Reference 465