PVA-3000 Reference Manual
December 2, 2019
Sifos Technologies
Page
16
1.3.5.
Transmit Level Measurement
Transmit Level
(or transmit power) is a bulk measurement of the
power
of a
transmitted signal. This measurement is a factory calibrated and normalized
such that a 0 dB reading for 100BaseTx corresponds to a nominal, 2Vpp, 4
nsec Rise/Fall time transmitted signal and a 0 dB reading for 1000BaseT
corresponds to a nominal peak-to-peak voltage of 1.5V from Point A to Point B
on the gigabit Test Signal #1 (
see Figure 1.11
).
Transmit Level (also referred to as
Tx Level
) should be thought of as the
integrated power within the full signal spectra as compared with that of a
nominally powered signal. It bears an approximate relationship with the peak-
peak level of a transmitted signal, though as stated in Section 1.3.3, the peak-
peak voltage will relate more closely to lower frequency power (e.g. 2 MHz
PSD) than to the wide-band power measurement made with this meter.
The Tx Level measurement is used inside of PSD calibrations to assure a more
accurate zero dB baseline to PSD measurements. When evaluating Ethernet
ports, Transmit Level is a quick indication of total signal power relative to a
nominal 100BaseTx or 1000BaseT signal. It will respond dB-for-dB if a fixed,
flat frequency power loss (or pad) is placed in line with an Ethernet transmitter.
1.3.6.
Pair Skew Measurement
The Pair Timing Skew measurement is only applicable in 1000BaseT links.
This meter very simply reports the timing differences between the 4 incoming
pairs (
see Figure 1.12
). Measurements are reported in nanoseconds and are
normalized to one of the four pairs meaning one pair will always read zero
nsec. Meter granularity is 8 nsec, or one symbol period.
The IEEE standard requires that delays between the four pairs should never
exceed 50 nsec. This equates to just over 6 symbol periods. This requirement
exists to assure receivers can properly reassemble data streams split amongst
the four pairs.
1.3.7.
Interface Verification
– Overview
The PhyView Analyzer will verify two types of interface characteristics while linked at 1000BaseT.
Bulk Return Loss (or Echo)
Bulk Pair-Pair Crosstalk
These characteristics are separated from Transmitter and Receiver testing since they are not strictly related to the PHY
transmitter or receiver. The measurements made required that the port-under-test support gigabit Ethernet. The
values obtained however are not likely related to link rate and are generally applicable at any of the link rates 10, 100,
or 1000BaseT. Of course, 10BaseT is much less sensitive to return loss or crosstalk because of it’s relative narrow
frequency band.
1.3.8.
Bulk Return Loss (Echo) Measurements
Bulk Return Loss
(or Echo Response) is a measure of the power ratio between transmitted power and incident
reflected power. Transmitted power is reflected whenever there are discontinuities or mismatches in the transmission
path of a signal. 10/100/1000BaseT interfaces are designed for 100
transmission paths meaning that source and
termination impedances, as well as characteristic impedance, are nominally 100
over the applicable frequency range.
The term “bulk” indicates that the measurement is not reported as a function of frequency. It is simply a wideband
bulk power ratio. It is available only in 1000BaseT because that technology was designed to enable signal power
measurements that are correlated only to a specific transmission direction on a specific pair. In other words, the Bulk
Return Loss measurement takes advantage of features that are unique to 1000BaseT.
100BaseTx:
0 dB
1000BaseT:
0 dB
Test Signal #1
2.000 Vpp
4.0 nsec
1.500 Vpp
A
B
Mask
100BaseTx:
0 dB
1000BaseT:
0 dB
Test Signal #1
2.000 Vpp
4.0 nsec
1.500 Vpp
A
B
Mask
Figure 1.11
Zero dB Transmit Level
-16
nsec
-8
nsec
0
nsec
-16
nsec
-8
nsec
0
nsec
Figure 1.12
Pair Timing Skew
Summary of Contents for PhyView PVA-3000
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