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Indianapolis, Indiana, May 5, 2025 - Copper Mountain Technologies' (CMT) Brian
Walker, Sr. RF Engineer, SME, has published a new white paper entitled "Hardware Triggering
a Vector Network Analyzer." In it, he details the use of hardware triggering in
VNAs to synchronize measurements with external test equipment, such as
programmable power supplies or pulsed RF signals. It explains how external
triggering - either "On Sweep" or "On Point" - enables precise control over VNA
operations, reducing power dissipation in devices like RF power amplifiers. The
paper outlines SCPI commands for automation, including triggering, polling data,
and checking VNA status, with examples in Python-like syntax. It also covers
trigger voltage levels, polarity settings, and timing modes, including
programmable delays for pulsed RF measurements. The document highlights Copper
Mountain Technologies' VNAs, which support these features alongside advanced
analytical functions like time-domain processing.
CMT has a growing list of
Technical Resources (white papers and videos) to assist you in getting the
most out of your test equipment, including exploiting some features you might
not be aware of.
Hardware Triggering a Vector Network Analyzer
Brian Walker, Sr. RF Engineer, SME
Figure 1 - Trigger on Point with Delay.
CMT Cobalt Series Vector Network Analyzer Direct Receiver
Access Power Amplifier Measurements.
Introduction
External triggering, or hardware triggering is a useful feature for a Vector
Network Analyzer (VNA). It allows synchronization of the VNA to other test equipment
in a test system. For instance, an RF power amplifier might need to be measured
with various bias voltages and drain currents. A programmable power supply might
step through a voltage range, triggering a VNA sweep at each step. An RF power amplifier
(PA) can be tested with pulsed RF instead of a continuous signal, with the VNA triggered
at each pulse to perform a measurement. This greatly reduces the average power dissipation
of the PA so that it can be measured without active cooling measures.
SCPI Commands for Automating VNA
If a Vector Network Analyzer is externally triggered, an automation script will
likely also be used to capture the data. With the socket server enabled, the VNA
will listen on the default port 5025 for SCPI commands, which are sent as readable
ASCII characters and defined in the instrument's operating manual. The manual describes
SCPI commands for setting all measurement parameters and retrieving measured data.
Many scripting platforms can be used: Python, C++, C#, Matlab, and LabView among
others.
External Triggering Using SCPI Commands
External triggering can be "On Sweep" or "On Point." In On Sweep mode, the Vector
Network Analyzer performs one entire sweep from start to stop frequencies, then
returns to the start frequency and holds, waiting for the next trigger. Completed
sweep data can be polled from the VNA using SCPI commands. Those commands are as
follows:
query("TRIG:WAIT MEAS;*OPC?") * Wait for measurement to start query("TRIG:WAIT
WAIT;*OPC?") * Wait for it to complete
Alternatively, the state of the VNA, actively sweeping or paused, may be determined
by inspecting the status register.
query("STAT:OPER:COND?")
A reply of 32 means paused and waiting for trigger, and 16 means the VNA is still
measuring/sweeping.
Then, getting the frequency array:
query("SENS1:FREQ:DATA?")
And getting the data:
query('CALC1:TRAC1:DATA:SDAT?') * Assuming trace 1 data from channel 1
These are just the SCPI commands relevant to triggering and getting the measurement.
A great deal of additional functionality is possible.
Trigger Levels
The external trigger may be +3.3V or +5V. A logic "high" is higher than +2.6V,
and a logic "low" is less than +1.1V. The external trigger's polarity may be positive
or negative. Triggering will occur on a positive trigger's low-to-high transition
and a negative trigger's high-to-low transition, depending on the "Positive" or
"Negative" trigger setting.
Trigger on Sweep vs Trigger on Point
For the "Trigger on Sweep" mode, each external trigger causes a new sweep. "Trigger
on Point" causes only a single frequency point to be measured. If a sweep contains
1001 points, there must be 1001 triggers to measure each point and complete the
sweep.
Other trigger settings are "Before Sampling" and "Before Setup". If "Before Setup"
mode is set, the trigger will cause the VNA to move from the last frequency to the
new frequency, settle in, and then make the measurement. If "Before Sampling" mode
is set, the VNA will have already moved to the new frequency and settled, and the
measurement will begin immediately.
A delay after the external trigger may also be programmed. In the "Before Setup"
mode, the programmed delay will occur before the new frequency step begins. In the
"Before Sampling" mode, the measurement will not start until this delay is complete.
This is convenient for measuring the S-parameters of a pulsed RF signal. The vector
network analyzer measurement can be delayed until the stimulus signal has settled
after the rising edge.
Copper Mountain Technologies offers many Vector Network Analyzers. Nearly all
of them may be triggered externally and come with advanced analytical features such
as time domain processing, time domain gating, and frequency offset measurement.
Visit the Copper Mountain Technologies website to see the full line of products.
About Copper Mountain Technologies
Copper Mountain Technologies
develops innovative RF test and measurement solutions for engineers all over the
world. It is based in Indianapolis with sales offices in Singapore, London, and
Miami. The company pioneered metrology-grade USB VNAs in 2011 and continues to push
for innovation and change in the industry, offering a broad range of USB vector
network analyzers, calibration kits, and accessories for 50 Ohm and 75 Ohm impedance
from 9 kHz to 110 GHz. The VNAs use software for Windows® or Linux®
operating system on an external computer, PC, or tablet. CMT VNAs are used by engineers
in defense, automotive, materials measurement, medical, broadcasting, telecommunications
and other industries. All CMT VNAs include application and automation support, and
years of our engineering expertise at your disposal.
Contact Info
Copper Mountain Technologies
631 East New York Street
Indianapolis, IN
46202 | USA
Phone: 1-317-222-5400
Web: www.coppermountaintech.com
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