PXI-2549 2.7 GHz Dual-Terminated SPDT PXI RF Relay Module
The PXI-2549 is a 2.7 GHz, 50 Ω PXI RF relay module designed for automated RF testing, source selection, instrument protection and signal routing. It provides two independent terminated single-pole double-throw relay banks.
Each bank includes normally closed, normally open and common RF connections with integrated 50 Ω termination resistors. These terminations reduce reflections on inactive paths and help protect connected RF sources, devices under test and measurement instruments.
Key Features of the PXI-2549
- Two independent terminated SPDT RF relay banks
- DC to 2.7 GHz switching bandwidth
- 50 Ω nominal characteristic impedance
- NC, NO and COM connections for each bank
- Integrated 50 Ω termination resistors
- Six gold-plated SMA female connectors
- 30 V maximum switching voltage
- 0.5 A maximum switching or carry current
- 10 W maximum channel-to-common RF power
- 1.5 W termination power at 25°C or lower
- Less than 1.5 dB insertion loss through 2.7 GHz
- Less than 1.5 channel-to-common VSWR through 2.7 GHz
- Greater than 45 dB typical isolation through 2.7 GHz
- Less than 15 ps typical channel-to-channel skew
- 1 ns typical propagation delay
- 80 ps typical rise time
- Latching electromechanical RF relays
- Onboard relay-count tracking
- PXI hardware trigger support
- NI-SWITCH and NI Switch Executive compatibility
PXI-2549 Technical Specifications
| Product Model | PXI-2549 |
|---|---|
| Part Number | 778572-49 |
| Product Type | Terminated PXI RF relay module |
| Topology | Dual terminated SPDT |
| Number of Relay Banks | 2 |
| Connections per Bank | Normally closed, normally open and common |
| Termination | Integrated 50 Ω termination resistors |
| Frequency Range | DC to 2.7 GHz |
| Characteristic Impedance | 50 Ω nominal |
| Maximum Switching Voltage | 30 V |
| Maximum Switching Current | 0.5 A per channel |
| Maximum Carry Current | 0.5 A per channel |
| Maximum Channel-to-Common RF Power | 10 W |
| Maximum Termination Power | 1.5 W at 25°C ambient or lower |
| Minimum Switch Load | 0 dBm |
| Initial DC Path Resistance | Less than 0.25 Ω, typical |
| End-of-Life Path Resistance | 1 Ω or greater, typical |
| Insertion Loss Through 1 GHz | Less than 0.8 dB; less than 0.7 dB typical |
| Insertion Loss Through 2.7 GHz | Less than 1.5 dB; less than 1.35 dB typical |
| Channel-to-Common VSWR Through 1 GHz | Less than 1.3; less than 1.2 typical |
| Channel-to-Common VSWR Through 2.7 GHz | Less than 1.5; less than 1.4 typical |
| Isolation Through 1 GHz | Greater than 55 dB, typical |
| Isolation Through 2.7 GHz | Greater than 45 dB, typical |
| Channel-to-Channel Skew | Less than 15 ps, typical |
| Propagation Delay | 1 ns, typical |
| Rise Time | 80 ps, typical |
| Maximum Relay Operate Time | 10.4 ms |
| Mechanical Relay Life | 1 × 106 cycles |
| Electrical Relay Life | 3 × 105 cycles at 30 V, 10 mA resistive |
| Relay Type | Electromechanical, latching |
| Input Trigger Sources | PXI trigger lines 0 through 7 |
| Minimum Input Trigger Pulse Width | 150 ns with digital filtering enabled |
| Output Trigger Destinations | PXI trigger lines 0 through 7 |
| Output Trigger Pulse Width | Software selectable from 1 µs to 62 µs |
| Front-Panel Connectors | Six gold-plated SMA female connectors |
| Bus Connection | PXI Hybrid |
| PXI Power Requirement | 3.7 W at 5 V and 0.3 W at 3.3 V |
| Module Format | 3U, one-slot PXI/cPCI module |
| Dimensions | 21.6 cm × 2.0 cm × 13.0 cm |
| Weight | 255 g |
| Operating Temperature | 0°C to 55°C |
| Storage Temperature | -40°C to 71°C |
| Software Support | NI-SWITCH and NI Switch Executive |
PXI-2549 Part Number and Accessories
| Item | Part Number | Description |
|---|---|---|
| PXI-2549 | 778572-49 | 2.7 GHz, 50 Ω, dual-terminated SPDT PXI RF relay module |
| SMA 100 Flexible Cable | 763443-01 | 0.15 m SMA male-to-SMA male flexible RF cable |
| SMA 100 Flexible Cable | 763444-01 | 0.45 m SMA male-to-SMA male flexible RF cable |
| MCX-to-SMA Cable | 188377-0R3 | 0.3 m MCX plug-to-SMA plug RF cable |
| MCX-to-SMA Cable | 188377-01 | 1 m MCX plug-to-SMA plug RF cable |
| SMA Torque Wrench | 187106-01 | Torque wrench for correctly installing SMA connectors |
| SMA-to-SMB Adapter | 779674-01 | SMA plug-to-SMB jack RF adapter |
The PXI-2549 provides six front-panel SMA connectors. Each of the two SPDT banks has one NC, one NO and one COM connection. The module already includes internal termination resistors, so external terminations are not normally required for its internally terminated paths.
Dual-Terminated SPDT Architecture
The PXI-2549 contains two independently controlled SPDT relay banks. Each bank routes a common RF connection between a normally closed path and a normally open path.
The unselected path is connected to an internal 50 Ω termination resistor. This helps maintain a controlled impedance and reduces reflections from inactive ports.
Because the two banks operate independently, the module can perform two separate source-selection, instrument-selection or bypass-switching functions.
SPDT Form C Operation
An SPDT relay is a single-pole double-throw switch. The common connection acts as the pole, while the NC and NO terminals provide the two possible signal paths.
Software transfers COM between NC and NO. This can select between two RF sources, two devices under test or two measurement instruments.
The changeover architecture can also insert or bypass an RF component such as a filter, amplifier, attenuator or calibration standard.
Integrated 50 Ω Termination
Each PXI-2549 relay bank includes termination resistors for the inactive RF path. These resistors provide a 50 Ω load rather than leaving the unselected connection open.
Proper termination reduces reflected RF energy and can help protect signal generators, amplifiers, DUT outputs and other sensitive RF equipment.
The internal terminations are especially valuable when a signal source remains active while the relay routes the common connection to the other path.
Termination Power Rating
Each internal termination can dissipate up to 1.5 W of continuous RF power when the ambient temperature is 25°C or lower.
The terminations cannot withstand the module’s full 10 W channel-to-common rating. Applying 10 W directly to a terminated inactive port can permanently damage the termination.
Termination power must be reduced when the ambient temperature rises above 25°C. Use the official termination-derating curve to determine the permissible continuous power.
Termination Power Derating
The termination’s power-handling capability decreases as ambient temperature increases. This prevents the internal resistor from exceeding its thermal limit.
Applications operating above 25°C should calculate the maximum power delivered to every inactive port. Adequate PXI chassis cooling and unobstructed airflow are essential.
If the expected inactive-path power exceeds the derated limit, reduce the RF output before switching or use a different external termination arrangement.
DC to 2.7 GHz Frequency Coverage
The PXI-2549 can route signals from DC through 2.7 GHz. This frequency range supports wireless testing, communications equipment, RF component characterization and general-purpose automated RF systems.
Insertion loss, VSWR and isolation vary with frequency. The complete switching system should be evaluated at its highest operating frequency.
50 Ω Characteristic Impedance
The module has a nominal characteristic impedance of 50 Ω, matching most RF signal generators, analyzers, power meters and communication test equipment.
Use 50 Ω coaxial cables, adapters and fixtures throughout the complete RF path. Mixing 50 Ω and 75 Ω components can increase reflections and measurement error.
Insertion Loss Performance
Insertion loss represents the amount of RF signal power lost through the selected relay path. Lower insertion loss allows more of the original signal to reach the DUT or measurement instrument.
Through 1 GHz, insertion loss is specified below 0.8 dB, with a typical value below 0.7 dB. Through 2.7 GHz, it remains below 1.5 dB, with a typical value below 1.35 dB.
External cable, adapter and connector losses must be added when calculating the total system path loss.
Channel-to-Common VSWR
Voltage standing wave ratio indicates the impedance match between a selected channel and its common connection. A value closer to 1 represents less reflected RF power.
The PXI-2549 has specified channel-to-common VSWR below 1.3 through 1 GHz and below 1.5 through 2.7 GHz. Typical values are below 1.2 and 1.4 respectively.
Correct SMA connector torque, clean interfaces and suitable cables help preserve system-level VSWR.
Termination VSWR
Termination VSWR describes how closely an internally terminated port matches the nominal 50 Ω impedance.
A good termination match reduces reflected energy from the inactive path. Actual performance also depends on the connected cable, adapter and source output impedance.
When testing sensitive RF sources, verify termination performance across the complete application frequency range.
RF Isolation
Isolation measures how effectively the relay prevents RF energy from coupling into the unselected signal path.
Typical isolation is greater than 55 dB through 1 GHz and greater than 45 dB through 2.7 GHz.
High isolation reduces leakage between sources, DUTs and instruments. External cable placement, fixture shielding and grounding also affect system-level isolation.
Channel-to-Channel Skew
The PXI-2549 provides typical channel-to-channel skew below 15 ps. Low skew helps maintain consistent timing when similar signals are routed through different relay banks.
External cable-length differences can introduce additional skew. Use equal-length or phase-matched cables when phase and timing alignment are important.
Propagation Delay and Rise Time
The typical propagation delay is 1 ns, while the typical 10% to 90% rise time is 80 ps.
Propagation delay should be included in applications requiring precise timing alignment. The complete delay includes the relay, coaxial cables, adapters and fixture connections.
10 W RF Path Power
The maximum RF power through a selected channel-to-common path is 10 W. This rating is also limited by the maximum 30 V switching voltage and 0.5 A current.
The 10 W rating does not apply to the internal termination resistors. Terminated paths are limited to 1.5 W at 25°C or lower and require additional derating at higher temperatures.
30 V and 0.5 A Ratings
The PXI-2549 supports a maximum switching voltage of 30 V and maximum switching or carry current of 0.5 A per channel.
Voltage, current and RF power limits apply simultaneously. The module should not be used if any individual rating can be exceeded.
Switching Active RF Signals
NI recommends avoiding active RF switching whenever possible. During relay operation, the path is momentarily unterminated before the internal termination or alternate signal route is established.
This temporary mismatch can reflect energy toward the RF source. Reduce or disable RF output power before changing routes when required by the source documentation.
Switching active RF signals below 0 dBm may also reduce relay life and degrade signal integrity.
Latching Electromechanical Relays
The PXI-2549 uses latching electromechanical RF relays. Once commanded, the relay retains its position without requiring continuous coil power.
Latching operation reduces steady-state power consumption and internal heat. The application should explicitly initialize both relay banks when the PXI system starts.
Relay Operating Time
The maximum relay operating time is 10.4 ms. Some applications may require additional settling time before making an RF measurement.
Total test time also depends on RF source stabilization, analyzer acquisition time, DUT response and trigger configuration.
Relay Life and Count Tracking
The mechanical relay life is rated at up to one million operations. Expected electrical life is approximately 300,000 cycles when switching a 30 V, 10 mA resistive load.
Actual life depends on voltage, current, RF power and whether active signals are switched.
Onboard relay-count tracking helps maintenance teams identify heavily used paths, estimate remaining service life and reduce unexpected system downtime.
PXI Hardware Triggering
The PXI-2549 accepts input triggers from PXI trigger lines 0 through 7. With digital filtering enabled, the minimum input-trigger pulse width is 150 ns.
Output triggers can be routed to PXI trigger lines 0 through 7, with software-selectable pulse width from 1 µs to 62 µs.
Hardware triggering allows RF relay operations to be synchronized with signal generators, analyzers and other PXI instruments.
Typical PXI-2549 Applications
- Automated RF signal routing
- Protected RF source selection
- RF analyzer input selection
- Signal-path bypass switching
- Filter and amplifier insertion
- RF source protection
- DUT output termination
- Wireless device validation
- Receiver and transmitter testing
- Antenna-path switching
- RF component characterization
- Communications equipment testing
- Laboratory RF automation
Protected RF Source Selection
Each relay bank can select between two RF sources and route the selected source to one common output. The inactive source path receives an internal 50 Ω termination.
This helps reduce reflections and provides a defined load for the unselected source, provided its output power remains within the termination rating.
RF Analyzer Input Selection
The common connection can be routed between two DUT signals. The inactive DUT path is terminated to help control impedance and reduce reflections.
With two independent banks, the module can provide two separate analyzer, receiver or power-meter selection functions.
Filter and Amplifier Bypass Testing
A relay bank can route an RF signal through a filter or amplifier in one state and through a bypass path in the other.
This allows direct software-controlled comparison of gain, insertion loss, frequency response and other component characteristics.
DUT Output Termination
The integrated terminations can provide a defined load for an inactive DUT output. This can be important when the DUT must not operate into an open circuit.
Verify that the DUT output power remains below the termination’s temperature-dependent power rating.
RF Instrument Protection
Internal terminations help reduce severe reflections that may affect RF signal generators, amplifiers and DUT outputs. They are not a substitute for overvoltage, overpower or reverse-power protection.
The test system should still include suitable attenuators, limiters or external protection when the source can exceed the PXI-2549 ratings.
NI-SWITCH Software Support
The PXI-2549 is controlled through the NI-SWITCH instrument driver. NI-SWITCH provides functions for initializing the module, selecting relay routes, disconnecting paths and configuring hardware triggers.
The driver supports LabVIEW, LabWindows/CVI and compatible text-based programming environments. It can also be integrated into NI TestStand automated test sequences.
NI Switch Executive Integration
NI Switch Executive allows engineers to define meaningful route and route-group names instead of controlling physical relay connections directly in application code.
Named routes simplify systems containing multiple RF switches, sources, analyzers and DUT interfaces. Route validation can help prevent conflicting or invalid connections.
PXI Chassis Integration
The PXI-2549 occupies one slot in a compatible PXI or PXI hybrid-slot chassis. It can operate with RF generators, analyzers, digitizers and other NI PXI modules.
Before installation, verify chassis compatibility, controller communication, cooling, SMA cable clearance and the installed NI-SWITCH version.
PXI-2549 Troubleshooting
The PXI-2549 is not detected in NI MAX
Confirm that the module is fully installed in a compatible PXI slot. Check chassis power, controller communication and NI-SWITCH installation, then restart NI Measurement & Automation Explorer.
A relay bank does not switch between NC and NO
Verify the bank name and route command. Check the corresponding NC, NO and COM cables, connected instruments and external fixture wiring.
The internal termination becomes too warm
Check the RF power delivered to the inactive port and the ambient temperature. The 1.5 W termination rating applies only at 25°C or lower and must be derated at higher temperatures.
The internal termination is damaged
Disconnect the RF source and verify that terminated-path power did not exceed the applicable limit. The internal termination cannot withstand the full 10 W channel-to-common rating.
Insertion loss is higher than expected
Inspect SMA connectors, cables and adapters for damage, contamination or incorrect torque. Include all external cable and fixture losses in the system calculation.
VSWR is too high
Verify that the complete signal path uses 50 Ω components. Check SMA connector torque, cable condition, source impedance and the condition of the internal termination.
Isolation is lower than expected
Review external cable separation, shielding and grounding. Check whether RF energy is coupling through connected instruments, fixtures or DUT wiring.
The RF source becomes unstable during switching
Reduce or disable RF output before changing relay states. The path is momentarily unterminated during relay operation and may reflect energy toward the source.
Measurements differ between the two banks
Compare cable length, connector condition and external fixture design. Apply path-specific insertion-loss correction when necessary.
A relay becomes intermittent
Inspect the SMA connector and cable first. Review relay-count information and measure the path resistance to determine whether the internal relay requires service.
PXI-2549 Comparison with Similar RF Switch Modules
| Model | Primary Configuration | Best Suited For |
|---|---|---|
| PXI-2545 | Terminated 4×1 RF multiplexer | Routing four RF channels to one terminated common path |
| PXI-2546 | Dual 4×1 RF multiplexer | Routing two independent groups of four RF signals |
| PXI-2547 | 2.7 GHz, 50 Ω, 8×1 RF multiplexer | Connecting eight RF signals to one shared instrument |
| PXI-2548 | Four independent nonterminated SPDT relays | Maximum flexibility for four two-way RF paths |
| PXI-2549 | Two independent terminated SPDT relays | Two-way RF switching with protected inactive paths |
PXI-2549 vs PXI-2548
The PXI-2549 provides two terminated SPDT relay banks, while the PXI-2548 provides four nonterminated SPDT banks.
Choose the PXI-2549 when internal 50 Ω termination and source protection are important. Choose the PXI-2548 when four independent paths are needed and external termination can be used where required.
PXI-2549 vs PXI-2545
Both modules provide internally terminated RF paths. The PXI-2549 contains two independent SPDT banks, while the PXI-2545 provides a fixed terminated 4×1 multiplexer topology.
Choose the PXI-2549 for two separate changeover paths. Choose the PXI-2545 when four RF channels must share one common connection.
PXI-2549 vs PXI-2547
The PXI-2549 provides two terminated SPDT banks, while the PXI-2547 provides one nonterminated 8×1 multiplexer.
Choose the PXI-2549 for protected two-way switching. Choose the PXI-2547 when maximum multiplexer channel count is more important than internal termination.
Recommended Related Products
- PXI-2545 Terminated 4×1 RF Multiplexer Module
- PXI-2546 Dual 4×1 RF Multiplexer Module
- PXI-2547 2.7 GHz 8×1 RF Multiplexer Module
- PXI-2548 Quad SPDT RF Relay Module
- View More NI PXI and PXI Express Modules
Selecting the Right PXI RF Switch
Choose the PXI-2549 when the application requires two independent SPDT RF paths, DC-to-2.7 GHz coverage, 50 Ω impedance and internal terminations for inactive ports.
Choose the PXI-2548 when four independent nonterminated SPDT paths are required, or select a fixed RF multiplexer when several channels must share one common instrument.
Why Choose the PXI-2549?
- Provides two independent terminated SPDT relay banks
- Routes RF signals from DC through 2.7 GHz
- Maintains 50 Ω characteristic impedance
- Terminates inactive paths to reduce reflections
- Helps protect RF sources and DUT outputs
- Offers low insertion loss and controlled VSWR
- Provides greater than 45 dB typical isolation at 2.7 GHz
- Uses six gold-plated SMA connectors
- Includes onboard relay-count tracking
- Supports PXI hardware triggering
- Integrates with NI-SWITCH and NI Switch Executive
Frequently Asked Questions
What is the PXI-2549?
The PXI-2549 is a 2.7 GHz, 50 Ω PXI RF relay module containing two independent terminated SPDT switching banks.
What is the PXI-2549 topology?
It provides two terminated SPDT relays. Each bank has normally closed, normally open and common connections.
What frequency range does the PXI-2549 support?
The module routes signals from DC through 2.7 GHz.
Does the PXI-2549 terminate inactive paths?
Yes. Integrated 50 Ω termination resistors provide a defined load for the unselected paths.
What is the internal termination power rating?
Each termination can dissipate up to 1.5 W continuously at an ambient temperature of 25°C or lower. The rating must be reduced at higher temperatures.
Can the internal termination handle 10 W?
No. The 10 W rating applies to the selected channel-to-common path. The internal termination has a lower power rating.
What is the insertion loss at 2.7 GHz?
Insertion loss is specified below 1.5 dB through 2.7 GHz, with a typical value below 1.35 dB.
What is the VSWR at 2.7 GHz?
Channel-to-common VSWR is specified below 1.5 through 2.7 GHz, with a typical value below 1.4.
How many SMA connectors are provided?
The module provides six gold-plated SMA female connectors: three for each terminated SPDT bank.
Should active RF signals be switched?
NI recommends avoiding active RF switching when possible because the path is momentarily unterminated during relay operation.
Which software controls the PXI-2549?
The module is controlled through NI-SWITCH and can be integrated into named-route applications using NI Switch Executive.
What is the PXI-2549 part number?
The standard NI part number for the PXI-2549 is 778572-49.
Request a Quote for the PXI-2549
Contact us for current availability, lead time and project pricing for the PXI-2549 2.7 GHz Dual-Terminated SPDT PXI RF Relay Module. We can also help identify compatible SMA cables, adapters, PXI chassis and related NI RF switch modules for your automated test system.
