Positive Train Control (PTC)

 Positive train control (PTC) is a North American system of functional requirements for monitoring and controlling train movements to help prevent train-to-train collisions, derailments caused by excessive speeds, unauthorized train movements in work zones, and the movement of trains through switches left in the wrong position. Over a decade ago, Congress mandated the implementation of PTC by certain railroads in response to the Rail Safety Improvement Act of 2008 (RSIA) (the deadline of which has been extended out to December 31, 2020).

The main concept of PTC (as defined for North American Class I freight railroads) is that the train receives information about its location and where it is allowed to safely travel, also known as movement authorities. Equipment on board the train then enforces this and prevents unsafe movement. PTC systems may work in either dark territory or signaled territory, and may use GPS navigation to track train movements.

Currently 42 railroads are required by statute to implement PTC systems, including Amtrak, commuter, and freight railroads. The technology is required to be implemented on approximately 60,000 miles of the 140,000-mile railroad network. This will involve approximately 20,000 locomotives, 24,000 waypoints with unique digital addresses, back office servers, and new interoperable secure wireless network with more than 400,000 components (Note: this deployment does not take into account commuter light rail systems).

The vast majority of the railroads subject to the mandate are implementing one of three PTC systems. In order for railroads to achieve full implementation, there are several stages of testing that must be completed – laboratory, field, and revenue service demonstration (RSD).

PTC ACSES Communication Setup

PTC ACSES provides railway trains with positive enforcement of speed restrictions based on the physical characteristics of the line. The on-board components keep track of a train’s position and continuously calculates a maximum safe braking curve for upcoming speed restrictions. If the train exceeds the safe braking curve, then the brakes are automatically applied. To achieve this, there is a communication chain between central control and the on-board equipment that must occur:

• The communication between the base radio unit (waypoint) and the mobile radio unit (radio installed on locomotive) starts with the central control sending ACSES commands to the base radio unit.
• The base radio unit’s communications manager converts the ACSES messages to the proprietary STFP protocol and sends it to the base radio hardware. The base radio hardware converts the STFP protocol to an over-the-air (OTA) signal and transmits it to the mobile radio unit.
• The mobile radio unit receives the OTA signal, converts it to an STFP protocol, and sends it to the mobile communications manager.
• The mobile communications manager converts the STFP bit-stream into ACSES messages and performs two functions: it sends back a response message to the base radio unit as needed as well as informs the on-board PC to actuate appropriate train action in response to the ACSES message (Figures 1 and 2).

Figure 1: PTC ACSES Communications Block Diagram

While most of the PTC ACSES signals within the block diagram are in a proprietary protocol, the OTA transmission enables the capturing of the message flow (transmit and receive between the base radio unit and the mobile radio unit) and, with the correct modulation decode capabilities, testing of the PTC ACSES system quality and accuracy. There are several tests that are important to verify that signals are being transmitted properly:

• Receive Signal Strength Indicator (RSSI): tests the RF received signal strength
• Error Vector Magnitude (EVM): ascertains the quality of the received ACSES data transmitted by the system
• Per Message Bit Error Rate (BER): based on the Forward Error Control (FEC) ensures the quality of the data received on a per message basis
• Cumulative Packet Error Rate (PER): verifies signal/data quality at the packet level.

Figure 2: PTC ACSES Message Flow Block Diagram

EVM, BER, and PER combined are important in order to determine if there are high data error rates and whether they happen in bunches (packet level) or are spread out over the data stream (BER). EVM will also correlate since it shows signal quality of the bits transmitted.

To perform these tests, use of a high-performance receiver/spectrum analyzer is ideal. These solutions provide technicians and engineers responsible for field testing with the ability to assess the performance of the PTC ACSES system by enabling several critical functions including:

• Decoding the message type, such as source of message (i.e., wayside) and destination type (i.e., office or central control)
• Capturing raw message payload data in hex (many rail system engineers are familiar with the hex messages sent and can quickly identify basic ACSES information from these hex messages)

Leveraging hex also enables other information to be captured and decoded (such as source and destination ATCS addresses, as well as time slot in frame and epoch), however, some of this information is dependent on the Comms Manager software loaded on to the radio units and the Comms manager control software on the PC side as this will determine what information is available to the rail system engineer. The ability to decode key messages is important in identifying individual trains and verifying that the ID being transmitted by a train’s PTC ACSES radio is correct. This is critical to safety within the system.

Figure 3: PTC ACSES Bench Testing Mobile Radio Block Diagram

Bench testing a mobile radio is useful to verify transmit and receive RF performance as well as troubleshoot problems with PTC ACSES radio performance. In order to bench test a PTC ACSES radio, users will need a tool that can generate specific PTC ACSES signals at various RF power levels to verify signal transmission and receive sensitivity at the radio. Users will also need to verify and validate signal quality. The use of the PTC ACSES communications manager software is also needed in addition to an analyzer and signal generator. The communications manager software will report the receive sensitivity BER of the radio (Figures 3 and 4).

Figure 4: PTC ACSES Signal Generator and Analyzer – Bench Testing Mobile Radio

PTC ACESE OTA Testing

OTA testing is basically the technique of capturing a signal and making a measurement between the base radio unit (waypoint) and mobile radio unit (locomotive/railcar). This is critical as this is the only way that a high-performance receiver/signal analyzer can access and analyze the otherwise secure PTC ACSES transmission. With a high-performance receiver/spectrum analyzer with PTC ACSES demodulation capabilities, along with the appropriate antenna (and possibly a filter), tuned in to the PTC ACSES transmit frequency, field engineers and technicians are able to measure and analyze the PTC ACSES signal quality and demodulate the messages (hex or ASCII) (Figures 5 and 6). This helps the field engineers validate proper PTC ACSES functionality as well as spot potential problems that the instrument can help troubleshoot.

Figure 5: PTC ACSES OTA Block Diagram

PTC ACSES Coverage Mapping

Coverage mapping is an essential tool in assessing a PTC ACSES signal environment and ensuring proper deployment, installation, and operation. Coverage mapping is used to verify signal strength and quality over a specific area by effectively monitoring RSSI and ACPR levels as well as conducting BER mapping. In the case of PTC ACSES, coverage mapping should be conducted over the various rail lines used for passenger rail as well as integrated lines with Class 1 commercial traffic. Coverage mapping can be performed with a high-performance receiver/signal analyzer with GPS option connected to the PTC ACSES radio’s antenna system to better simulate RF receive performance on the train under test through the rail network. The high-performance receiver/spectrum analyzer with mapping capabilities must also perform coverage mapping by accurately and simultaneously collecting key PTC ACSES signal quality measurements (such as EVM, BER, and RSSI data) for the PTC ACSES frequency under test, then plotting one of the parameters on to a map of the area/route being tested. As the information is in .kml format (Google maps), all three values can then be displayed on Google Maps to gain a clear insight into any areas that may need improved coverage to ensure seamless operation.

Testing Parameters

This section is focused on the parameters being measured during PTC wireless path testing in the field, what is normally being measured and how it can be improved. This section also describes the PTC testing features available on the Anritsu LMR Master. Several recommendations and testing tips are offered to improve the quality and accuracy of the testing and to fully utilize the features of the PTC Analyzer/Generator of the LMR Master.

Current field testing methodologies may address one or more of the following:

• Coverage, currently measured in RSSI
• Variable noise floor and de-sensing in some areas
• On-channel interference from other radios
• Near-channel interference from other radios
• Intermodulation products from other radios on several frequencies
• Random noise with different patterns from multiple sources
• Multipath fading caused by reflections on structures, terrain and large vehicles
• Other interference including radars, power lines and broadcasting systems

The main parameter currently measured is RSSI. One or more of the other parameters listed above may also be measured and recorded, but as of today there is no process in place to correlate how one or more interfering parameters might affect RSSI.

Field Testing

This section examines methodologies currently employed for PTC wireless path field testing, and provides several recommendations to change and improve the entire testing process, making it much faster and significantly reducing the cost of field testing work. Some semi-automated testing methods are proposed and described.

RSSI Testing (Current Testing Method)

RSSI provides a signal level resulting from the sum of multiple components that include the original signal received directly from the transmitter, other multipath signals produced by one or more reflections/bounces of the original signal on structures, terrain or other physical objects, plus any other signals from other radios, or products from different types of interference such as intermodulation or equipment noise, plus the ambient RF noise floor, which in densely populated areas may exceed –95 dBm.

An RSSI value can be estimated/extrapolated taking into consideration all the external factors, but it would not be very accurate or useful to determine how the PTC wireless path will be operating in the real world. There could be a section of 60 miles of track with a noise floor below –120 dBm, and almost perfect coverage of every foot of track with RSSI levels between –75 and –90 dBm, and there could still be large holes in coverage caused by multipath and other factors that degrade the PTC wireless path performance.

RSSI measurements only provide a small, one-dimensional view of the overall system performance. RSSI cannot discriminate between desired signals and undesired RF intereference, thus testing which relies solely on RSSI can lead to false consclusions, poor system performance, and added expense to diagnose and resolve failures. RSSI can be used as a secondary source for reference, but the primary testing has to be done using a more robust, precise testing method measuring the actual packet success performance of the PTC wireless path under test. This performance varies and so even with an adequate RSSI level there could be communications problems in the PTC wireless path.

BER Testing (Improved Methodology)

While it is indispensable to examine the ambient RF noise environment and establish how path characteristics affect performance of PTC radios; RSSI is not a measure of performance. The primary measurement used should be BER (Bit Error Rate), providing data packet success information. Instruments such as the LMR Master can simultaneously observe, geo-tag, and record BER, EVM (Error Vector Modulation) and RSSI measurements. The Anritsu LMR Master measures BER in percentage values, and the geo-tagged data is available as both an industry-standard KML and a CSV text file – both of which are easily manipulated by post-processing tools written in PERL and Python.

First step in the process is to determine a maximum acceptable BER figure for the PTC wireless path. This can be determined by setting up a PTC transmitter and a PTC receiver, and then observing packet success rates between the TX and RX radios while the RF path is deliberately degraded and the BER figure increases. The pair of radios will have to be carrying live PTC data traffic; the maximum acceptable BER for the PTC wireless path will be set at the point that this PTC data traffic quality of service becomes marginal. This maximum BER figure will be used as a benchmark for PTC wireless path measurements to be carried out in the field, and it will replace RSSI as the main parameter used to measure PTC wireless paths.

Any path measurement figures in excess of the maximum acceptable BER for PTC radios should be flagged for more detailed testing and analysis of that path. This testing will include verification of the actual path loss against the propagation prediction software for that path, and checking for the existence of interference, intermodulation, or other RF issues that might be causing unacceptably high BER values. It is possible that the path loss will be within the RSSI range expected from the values determined through propagation prediction software, but the BER values could still be beyond the maximum acceptable values to achieve packet success between the TX and RX radios; in this case the problem will be identified faster. The solution might involve mitigation by filtering or similar means, or the problem may ultimately require relocation of the base station to a better radio site, and/or deployment of additional base stations.

Some current PTC path measurements sometimes are done using PTC radios to measure BER, but the measurement range of these radios cannot provide the requisite depth of information. A typical PTC radio can only measure up to 1x10-4 or 1x10-5 BER, perhaps good enough for a quick snapshot, but not sufficient for formal PTC field testing. Radios are not designed to work as instruments; they are not calibrated to provide traceable measurements and they cannot emulate the multiple features and functions found on instruments specifically designed to carry out testing in the field.

When detailed analysis of a “flagged” PTC wireless path is required, the problem can be resolved by replacing the PTC transmitter in question with a transmitter consisting of an Anritsu S412E LMR Master transmitting PTC test signals into a 50 dB gain 100 watt power amplifier, and using another LMR Master to receive and analyze the PTC test signals. This will permit testing with variable TX power across a broad range of power levels, and it would be possible to observe BER values and how they change when TX power is gradually increased in small 1 dB steps from minimum measurable power to maximum power output, i.e., 75 watts.

If the transmitted power is slowly increased and the BER starts to deteriorate, this will point to the existence of path degradation due to the existence of power dependent RF issues such as intermodulation. This would be very difficult to discover when testing with RSSI alone or using PTC radios to measure BER

Interference and Noise Testing (Current Testing Method)

Current testing methods often identify RF issues caused by one or more factors that result in interference to PTC signals. With instruments such as the LMR Master it is possible to observe, measure and record with high accuracy a complete set of test data for each of the RF issues found and identified.

A list of these RF issues could include one or more of the following:

• Variable noise floor and de-sensing in some areas
• On-channel interference from other radios
• Near-channel interference from other radios
• Intermodulation products from other radios on several frequencies
• Random noise with different patterns from multiple sources
• Multipath fading caused by reflections on structures, terrain, vehicles
• Other interference including radars, power lines and broadcasting

In the current testing methodology, multiple measurements are taken in the field to identify, measure and record RF issues that may interfere with or degrade PTC signals. All these measurements are saved and can be used to render the RF issues in graphic format for further evaluation and analysis. However, even with precise measurements results and graphics, it will not be possible to determine to what the degree of impairment or degradation that each of these RF issues, or a combination of them, can cause to a wireless link carrying PTC signals.

In the real world it will not be possible, or practical, to address and resolve each and every RF issue identified and measured in the field. It will be necessary to rate each of these RF issues in terms of the amount of impairment that they introduce to wireless PTC data packet communications, and then decide which of the RF issues will be practical and/or cost effective to resolve, leaving other RF issues as they are.

In some cases it might be necessary to increase the number of base stations so that the PTC radio link signal level will be higher than interfering RF signals that cannot be resolved. In other cases, base stations will have to be re-located to other sites. A different testing methodology will be required, to determine the quality of service of a wireless PTC link, compare it with the performance predicted by coverage prediction software programs, and if that performance is not achieved, look for and resolve RF issues and other factors that might be responsible.

Interference and Noise Testing (Improved Methodology)

Initial testing will have to be based on BER performance/packet success, as described in Section 2.2. above. All testing will have to be done using BER, and those PTC wireless radio paths with performance below what was forecasted by propagation prediction programs will have to be further tested to determine if the lower performance than expected is due to radio link parameters, due to some type of interference, or a combination of both.

Before starting to test BER, a brief, cursory set of measurements could be taken to verify that there are no significant problems with one or more of the seven RF issues listed in the second paragraph of Section 2.3 above. No extensive testing and recording of measurements will be required for analysis of these seven RF issues.

The most important testing effort will be measuring BER of the PTC wireless path. It might be possible to do it using a PTC radio to transmit PTC test signals or, preferably a PTC test signal generator using amplified test signals as described in the paragraph below.

PTC packet success/performance BER testing can be done more accurately using two Anritsu LMR Master instruments, a PTC test transmitter, and a PTC test receiver used to measure a PTC wireless path. Readings are taken in BER and also in EVM and RSSI, with all results automatically recorded to digital storage memory.

Intermodulation measurements in locomotives and base stations

Locomotives and radio sites with multiple base stations present some unique intermodulation challenges requiring innovative approaches to measuring and addressing intermodulation issues. Most railroads operate multiple voice and data radios in unique, challenging environments. Locomotives typically have more than a dozen radios in multiple bands with all the antennas placed next to each other on the roof within a space of about 6 ft X 6 ft with no vertical separation. Locomotives are more like multi-radio, multi-frequency band “rolling base stations” than they are mobile radio platforms, which typically only have less than a handful of radios. (Most mobile systems only have one or two radios.)

The larger STB Class One railroads also have complex radio sites along the tracks with several different types of base stations for voice and data operating on different frequency bands. For example, a Class One railroad has an average of six base station radios per site. Antennas are more physically separated on radio towers than on the aforementioned locomotives, but the towers are typically crowded and antenna isolation can be a problem due to cross-coupling.

Intermodulation generated by the RX front end of several radios with their antennas located in close proximity to each other can be challenging to observe and track down to the origin, since there are several radio front ends generating intermodulation products. Many radios are simultaneously impacted by the transmissions of other radios, and intermodulation products are transmitted through the antenna of all radios, which in turn generates a “second wave” of intermodulation. The result is a large portion of spectrum across several bands which is affected by a high number of difficult to track intermodulation products.

An effective way to monitor and measure how much intermodulation is generated and transmitted by each of the multiple radio front ends is to use a bi-directional coupler to measure the RF energy entering and leaving each radio by connecting an Anritsu LMR Master alternatively to the TX and RX sensing ports of the coupler.

Using the LMR Master in PTC coverage analysis mode, with the onboard GPS receiver locked, it will be possible to move around while making measurements. BER, EVM, and RSSI data is gathered continuously, and five color-coded flags can be used to provide the operator real-time feedback on BER measurements being made.

Where the BER performance measured is lower than predicted, a secondary suite of measurements will be carried out. These measurements will include the RSSI figures recorded during the BER performance testing, and several other RF parameters. Extensive measurements focused on these RF issues will only be required if the performance testing indicates that the BER measurements along the PTC wireless path exceed the maximum acceptable BER values.

All these measurements can be carried out using Anritsu LMR Master instruments. Typically, several concurrent RF issues will be found which will make individual problems appear to be larger than they really are.

Using Anritsu LMR Master instruments, it will be possible to identify individual RF problems which can then be quantified and their causes identified so that technical teams can resolve each of them individually. In some cases, these issues might be mitigated by simply adding bandpass filters, increasing isolation between antennas, or removing/covering nearby rusty metal which can cause passive intermodulation (PIM).

After implementing mitigation countermeasures, the BER performance of the PTC radio link will be measured again. If it still falls below expected performance, another type of solution will have to be developed. Relocation of the PTC base station radio site or adding more PTC base station radios may be required.

The main difference between the current testing method and the proposed new method is that no extensive testing of RF issues will be carried out up front, only a brief check to verify that no major problems exist will be required. At the core of the testing effort will be the measurement of BER to determine if the path is capable of carrying PTC live data packet traffic. If the BER performance measurements indicate that the performance is below acceptable BER values, then more testing will be done to verify the RSSI level, and then look for any other RF issues that might be degrading the PTC wireless path.

When poor BER performance is detected and a path is flagged for more testing, precision measurements will be required. A team of field engineers with advanced skills will have to be deployed to the site. This team will have to carry all the instruments and equipment, set them up in the field, connect them, and carry out the testing under varying and likely adverse environmental and weather conditions. Extreme heat and cold, humidity, and dust may be present.

This is similar to the current testing methods used by some railroads, which may take several days or even weeks to complete. Several separate instruments have to be carried to the field in the area where testing has to take place, and a team of test engineers will have to travel and spend a considerable amount of time on site, even if they are only required or able to do testing for a small part of the time. Field testing is always challenging in that power supplies/systems have to be deployed and all instruments, attenuators, filters, etc have to be interconnected with a variety of connectors and cables that are used many times in different sites and require calibration for every single measurement session.

Cables laying on the ground or hanging from equipment and other structures often get damaged when their minimum bending radius is exceeded and kinks/dents are produced along the cable by nearby physical objects, changing the cable transmission characteristics and causing testing errors. Many connectors are also damaged during field work. Testing crews are aware that it is difficult to emulate a lab environment in the field, and are used to deal with variable or less than accurate results due to factors described above.

Current Testing Methods

Current testing methods can be very involved and time consuming, as well as quite expensive. They require the deployment of personnel and equipment to the field, setting up the instruments, laying cables on the ground, calibrating the instruments with the cables used, and trying to use similar testing procedures through several hundred to thousands of measurements that have to be taken. It is difficult to replicate the same testing procedures across several testing sites as each field deployment is different. Many tests involve manual readings and annotations of results by hand. Since the uninterrupted presence of PTC signals along the tracks with appropriate RSSI and low noise floor does not guarantee continuous coverage and operation of PTC systems, it is indispensable to test continuously along the tracks. Drive testing has to provide an uninterrupted set of measurements along the entire track section being measured.

Wireless path testing has to be done under various weather conditions and at different times and with different temperatures, then the results of all these tests need to be compared and final average or median values have to be determined to be documented as the results of the testing. This could tie up testing crews in the field for several days or even weeks to complete a single stretch of track. While this process is not cost effective, a bigger concern is the time it takes to complete the tests, due to the limited number of available staff with the requisite training. Class One railroads have approximately 60,000 miles of track equipped with ITC-R PTC, approximately 14,000 PTC base stations, and about 30,000 PTC waysides. Using current methods and with the available human resources to carry out the testing in the field, it might take several years to complete the testing, past the deadline set forth by the US Government to deploy and commission PTC systems. A new approach to testing has to be developed and implemented, including semi-automated testing that can be done much faster and using less testing staff.

Field Testing Recommendations – Remote Testing

A new testing approach has to be developed. First, start field testing with quick, cost effective “pass/fail” tests with semi-automated, remotely controlled test equipment verifying compliance or non-compliance of a PTC wireless path with a pre-established template. Flag the PTC Paths that fail, and only doing “in-depth” testing when required by deploying a team to the field with integrated equipment and instruments to work faster and more efficiently.

The testing methodology could use simple PTC base station radio transmitters to send PTC test signals, which would be measured by the LMR Master inside test equipment enclosures that would be traveling on regular freight trains. This would allow carrying out multiple measurements of a PTC wireless path at different times of the day, with different temperatures, and under various weather conditions.

When a PTC wireless path fails the first test, it will be flagged and a more comprehensive test will be done, this time using LMR Master PTC test signal generators with linear power amplifiers to simulate PTC radio transmitters, and LMR Master PTC signal analyzers.

Testing will be done from a Central Testing Facility (CTF) that will operate 24/7 and control the railroad’s PTC base stations along the tracks by remote control, turning PTC test signals TX on and off, changing channels, and also changing TX power in large steps of about 10 watts at a time. The CTF will also remotely access and control all test equipment and instrument enclosures in the field.

This testing will be done without testing staff in the field, and will be much more efficient, faster and precise than current field testing. This process is called “Remote Testing”, and will use LTE wireless broadband modems similar to what is used today in locomotives.

This first level of testing can be done simultaneously over several different sub-divisions across the entire railroad using remotely controlled equipment and instruments placed on the second unit of a freight train. Since all the testing will be controlled from a single CTF at each railroad, one single team of expert and similarly trained test engineers will be able to simultaneously operate several remote testing systems increasing testing efficiency several fold.

The equipment and instruments enclosures will be installed and removed from the locomotives by trained radio techs or locomotive electricians, without having to deploy to the field expert test engineers. The equipment will be anchored with a chain and padlock to the Conductor’s seat post, and the power will be obtained from the locomotive 72 VDC power system.

The transportable equipment and instruments enclosures will have solid state servers recording to solid state hard drives all the measurements. Even if communications are briefly interrupted the measurements will continue.

The process will be very similar to what was described in section 2.4, and in figure 3, except that instead of a team of field engineers moving along the tracks with the test equipment, the instruments will move inside a locomotive or other vehicle, with all the testing being controlled and done remotely from a CTF.

This effort will be facilitated by the use of color-coded flags produced by the LMR Master BER coverage testing process, with full BER, EVM and RSSI measurement details stored in solid state memory.

The “tiger team” will be equipped with kits of pre-configured, pre-calibrated instruments and equipment to carry out and complete testing and verification of a PTC wireless path in much less time than it currently takes to do it, transmitting the testing process and information in real time to the expert testing team in the central testing facility.

Anritsu LMR Master instruments can be controlled from a PC. These instruments are fully customizable and can be programmed in several different ways to provide the requisite functionality for PTC testing in the field, either by local or by remote access and control. The LMR Master has a built in remote web server that can be used to remotely operate the instrument via any modern web browser. All that is required is to connect the LMR Master to a network via an Ethernet connection.

Current RSSI testing is done mostly using a constant power transmitter such as a PTC radio base station, which makes it more difficult to observe the effect of RF issues whose presence and magnitude depend of the level of the transmitted power, such as intermodulation. PTC TX power should be fully adjustable in small increments such as in one dB step at the time. When a “tiger team” is deployed with instrument and equipment kits including a 100 W power amplifier, they will be able to excite the power amplifier from the LMR Master PTC signal generator, adjusting the TX power in increments of 1 dB.

Since the LMR Master instrument can be equipped to operate with FM and on NXDN™ radio systems, it will be possible to use a combination of an LMR Master transmitting FM or NXDN test signals and a 100 watt linear power amplifier to include in the testing process measurements on FM and NXDN radio systems; for example, to emulate and verify an NXDN system that might be causing interference to PTC systems when transmitting.

LMR Master instruments can also be equipped to operate with ETSI DMR and TETRA and with APCO Project 25 (aka P25) Phase 1 and Phase 2 systems, FirstNet LTE systems, and WiMAX™ (both Fixed and Mobile varieties).

The entire process can be expedited by pre-assembling all instruments and equipment in sturdy, shock- absorber mounted rack frame inside a clamshell transportable enclosure. All connectors will be gold plated and all cables would be double shielded RG 31DS type. Field deployment and testing will be completed in much less time, and with greater accuracy. Low-noise, 2 kilowatt gas powered portable inverter generators will be shipped to the field with each transportable enclosure. Figure 4 below shows a typical test system.

Products

S412E

Land Mobile Radio
500 kHz - 1.6 GHz VNA frequency
9 kHz - 1.6 GHz SPA frequency