USB-5681 Specifications

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Updated2025-06-23
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USB-5681 Specifications

These specifications apply to the USB-5681 .

All specifications are subject to change without notice.

Notice The protection provided by the USB-5681 can be impaired if it is used in a manner not described in this document.

Definitions

Warranted specifications describe the performance of a model under stated operating conditions and are covered by the model warranty.

Characteristics describe values that are relevant to the use of the model under stated operating conditions but are not covered by the model warranty.

Typical specifications describe the performance met by a majority of models.
Nominal specifications describe an attribute that is based on design, conformance testing, or supplemental testing.

Specifications are Typical unless otherwise noted.

Conditions

Minimum or maximum specifications are warranted under the following conditions unless otherwise noted.

1 hour warm-up time at ambient temperature
Calibration cycle maintained
Temperature 0 °C to 55 °C

USB-5681 Pinout

Use the pinout to connect to terminals on the USB-5681 .

The following figure shows both panels of the device.

Table 1. Information about the USB-5681 module back panel LED
LED	Indication
Green	The USB-5681 is connected to a computer or a chassis and is functioning properly.
Yellow	An error has occurred.
Off	The USB-5681 is not initialized.

Note The USB-5681 device has a USB 2.0 interface with a USB Type Mini-B port. You can remotely program the device using this USB interface. In addition to communication, the USB supplies power to the device. The interface is USB 2.0 and 1.1 compatible and operates with an interface speed of 12 Mb/s.

General

Frequency range

10 MHz to 18 GHz

Input range

- 40 dBm to +20 dBm

Input return loss
10 MHz to <150 MHz	>22.12 dB
150 MHz to 2 GHz	>24.94 dB
>2 GHz to 12 GHz	>20.08 dB
>12 GHz to 18 GHz	>19.08 dB

Figure 1. Power Meter Return Loss, Measured

Measurement range
Range 1	.+20 dBm to -7 dBm, typical
Range 2	-7 dBm to -40 dBm, typical

Signal-channel bandwidth

50 kHz

Uncertainty

Linearity

<3% (±0.13 dB)

Calibration factor^[1]¹ Expanded uncertainty with coverage factor K = 2 for absolute power measurements on a continuous wave (CW) signal at 0 dBm and calibration frequencies 10 MHz, 50 MHz, 100 MHz, 300 MHz, 500 MHz, and 1 GHz to 18 GHz, in 1 GHz increments.
10 MHz	<2.3% (±0.10 dB)
50 MHz to 18 GHz	<1.5% (±0.07 dB)

Noise^[2]² Expanded uncertainty with K = 2 after zero operation when measured with 1 average, and 20 ms aperture time for 5 minutes. Effect of noise can be reduced by increasing the number of averages and/or increasing the aperture time. Noise decreases at a rate equal to the square root of the number of averages and aperture time.
Measurement range 1	<8 μW (-21 dBm)
Measurement range 2	<40 nW (-44 dBm)

Zero set^[3]³ Expanded uncertainty with K = 2 after zero operation when measured with 1 average and 20 ms aperture time for 5 minutes.
Measurement range 1	<1 μW
Measurement range 2	<3 nW

Zero drift^[4]⁴ Expanded uncertainty with K = 2 after one hour warm-up and zero operation and one hour of operation, 1 average, 20 ms aperture time, and when keeping the temperature within ±1 ºC.
Measurement range 1	<0.5 μW
Measurement range 2	< 3 nW

Temperature compensation (0 °C to 50 °C)

<1.4% (±0.06 dB)

Effect of digital modulation^[5]⁵ Measurement error with reference to a CW signal of equal power and frequency at 25 ºC.
Power level ≥18 dBm	<1.4% (±0.06 dB)
Power level <18 dBm	<0.5% (±0.02 dB)

System

Measurement

Average power

Measurement resolution

0.01 dB

Offset range

-100 dB to +150 dB

Averaging

Averaging mode

Auto, repeat

Number of averages (repeat)^[6]⁶ Maximum number of averages allowed in Continuous mode and Time Slot mode is 40,000. In Scope mode, the maximum number of averages is equal to 8,231,936 divided by data points.

1 to 40,000

Auto-averaging
Resolution^[7]⁷ Averaging resolution of 0.001 dB is not available with the NI-568x SFP. This feature is only available when using the NI-568x instrument driver. Averaging resolution is defined as the place after the decimal to which the reading becomes stable.	1 dB, 0.1 dB, 0.01 dB, 0.001 dB
Source	Time Slot mode: 1 to 128 slots; Scope mode: 1 to 1,024 data points

Continuous Mode

Duty cycle correction	0.01% to 100%
Aperture time	0.01 ms to 300 ms
Measurement time^[8]⁸ Times based on benchmark results. Performance may vary based on your system.	(Number of Averages × a) + b, where a and b depend on the aperture time, as shown in the following table.

Table 2. Measurement Time Variables
Aperture Time	a (ms)	b (ms)
0.01	2	6.5
0.1	2.3	6.5
1	5.4	7.1
10	35.8	20.5
100	331	164

Scope Mode

Capture time	0.01 ms to 300 ms
Data points	1 to 1,024
Resolution	0.01 ms
Measurement time^[9]⁹ Times based on benchmark results. Performance may vary based on your system. Formula assumes averaging is set to 1, and trigger source is set to Immediate.	(Capture Time × 6.69) + (Data Points × 0.36 ms) + 13.6 ms

Time Slot Mode

Maximum number of slots

128

Slot width

0.01 ms to 100 m

Maximum capture time

300 ms (Slot Width × Number of Slots)

Resolution

0.01 ms

Exclusion periods^[10]¹⁰ The start exclusion time plus the end exclusion time must be less than the slot width.
Start exclusion	0 ms to 100 ms
End exclusion	0 ms to 100 ms

Trigger

Source^[11]¹¹ Software trigger not available in the NI-568x SFP. This feature is only available when using the NI-568x instrument driver. Internal and external triggers are not available when using Continuous acquisition mode.

Immediate, external, internal, software

Internal Trigger

Range	-20 dBm to +20 dBm
Level accuracy	±0.5 dB, typical
Slope	Positive or negative
Delay range	-5 ms to 10 s
Delay resolution	10 μs

External Trigger

Impedance	100 kΩ
Type	TTL/CMOS
Slope	Positive or negative
Delay range	-5 ms to 10 s
Delay resolution	10 μs
Voltage high threshold	2.0 V, typical
Voltage low threshold	1.2 V, typical
Hysteresis	0.8 V, typical
Maximum voltage	±20 V
Minimum pulse width	7.5 μs^[12]¹² The external trigger source is sampled approximately every 7.5 μs.

Maximum Damage Levels

Maximum DC voltage at RF port	±20 V
Absolute power	+30 dBm

DC Power Requirements (5 V) from Host USB

Typical current

450 mA

Caution You can impair the protection provided by the USB-5681 if you use it in a manner not described in this document.

Calibration

Interval

1 year; calibration interval starts with the date the product is put into service by the customer

Physical Characteristics

Dimensions	25 mm × 45 mm × 110 mm, excluding RF connector and silicone cover
Weight	230 g (0.51 lb)

Environmental

Specifications in this document are guaranteed under the following specified environmental conditions unless otherwise stated.

Maximum altitude	4,600 m (at 25 °C ambient temperature)
Pollution Degree	2

Indoor use only.

Operating Environment

Ambient temperature range

0 to 50 °C (Tested in accordance with MIL-PRF-28800F (Class 3).)

Relative humidity range^[13]¹³ Tested in accordance with MIL-PRF-28800F (Class 3). (noncondensing)
At 50 °C	45%
At 40 °C	75%
At 30 °C	95%

Storage Environment

Ambient temperature range	-40 °C to +71 °C (Tested in accordance with MIL-PRF-28800F (Class 3).)
Relative humidity range	5% to 95%, noncondensing (Tested in accordance with MIL-PRF-28800F (Class 3).)

Shock and Vibration

Operating Shock

30 g peak, half-sine, 11 ms pulse (Tested in accordance with MIL-PRF-28800F.)

Random Vibration
Random vibration nonoperating	10 Hz to 500 Hz, Power spectral density 0.03 g²/Hz (Tested in accordance with MIL-PRF-28800F.)

Compliance and Certifications

Safety Compliance Standards

This product is designed to meet the requirements of the following electrical equipment safety standards for measurement, control, and laboratory use:

IEC 61010-1, EN 61010-1
UL 61010-1, CSA C22.2 No. 61010-1

Note For safety certifications, refer to the product label or the Product Certifications and Declarations section.

Electromagnetic Compatibility

This product meets the requirements of the following EMC standards for electrical equipment for measurement, control, and laboratory use:

EN 61326-1 (IEC 61326-1): Class A emissions; Basic immunity
EN 55011 (CISPR 11): Group 1, Class A emissions
EN 55022 (CISPR 22): Class A emissions
EN 55024 (CISPR 24): Immunity
AS/NZS CISPR 11: Group 1, Class A emissions
AS/NZS CISPR 22: Class A emissions
FCC 47 CFR Part 15B: Class A emissions
ICES-001: Class A emissions

Note In the United States (per FCC 47 CFR), Class A equipment is intended for use in commercial, light-industrial, and heavy-industrial locations. In Europe, Canada, Australia, and New Zealand (per CISPR 11), Class A equipment is intended for use only in heavy-industrial locations.

Note Group 1 equipment (per CISPR 11) is any industrial, scientific, or medical equipment that does not intentionally generate radio frequency energy for the treatment of material or inspection/analysis purposes.

Note For EMC declarations, certifications, and additional information, refer to the Product Certifications and Declarations section.

CE Compliance

This product meets the essential requirements of applicable European Directives, as follows:

2014/35/EU; Low-Voltage Directive (safety)
2014/30/EU; Electromagnetic Compatibility Directive (EMC)
2011/65/EU; Restriction of Hazardous Substances (RoHS)
2014/53/EU; Radio Equipment Directive (RED)
2014/34/EU; Potentially Explosive Atmospheres (ATEX)

Product Certifications and Declarations

Refer to the product Declaration of Conformity (DoC) for additional regulatory compliance information. To obtain product certifications and the DoC for NI products, visit ni.com/product-certifications, search by model number, and click the appropriate link.

Environmental Management

NI is committed to designing and manufacturing products in an environmentally responsible manner. NI recognizes that eliminating certain hazardous substances from our products is beneficial to the environment and to NI customers.

For additional environmental information, refer to the Engineering a Healthy Planet web page at ni.com/environment. This page contains the environmental regulations and directives with which NI complies, as well as other environmental information not included in this document.

EU and UK Customers

Waste Electrical and Electronic Equipment (WEEE)—At the end of the product life cycle, all NI products must be disposed of according to local laws and regulations. For more information about how to recycle NI products in your region, visit ni.com/environment/weee.

电子信息产品污染控制管理办法（中国RoHS）

中国RoHS— NI符合中国电子信息产品中限制使用某些有害物质指令(RoHS)。关于NI中国RoHS合规性信息，请登录 ni.com/environment/rohs_china。(For information about China RoHS compliance, go to ni.com/environment/rohs_china.)

¹ Expanded uncertainty with coverage factor K = 2 for absolute power measurements on a continuous wave (CW) signal at 0 dBm and calibration frequencies 10 MHz, 50 MHz, 100 MHz, 300 MHz, 500 MHz, and 1 GHz to 18 GHz, in 1 GHz increments.

² Expanded uncertainty with K = 2 after zero operation when measured with 1 average, and 20 ms aperture time for 5 minutes. Effect of noise can be reduced by increasing the number of averages and/or increasing the aperture time. Noise decreases at a rate equal to the square root of the number of averages and aperture time.

³ Expanded uncertainty with K = 2 after zero operation when measured with 1 average and 20 ms aperture time for 5 minutes.

⁴ Expanded uncertainty with K = 2 after one hour warm-up and zero operation and one hour of operation, 1 average, 20 ms aperture time, and when keeping the temperature within ±1 ºC.

⁵ Measurement error with reference to a CW signal of equal power and frequency at 25 ºC.

⁶ Maximum number of averages allowed in Continuous mode and Time Slot mode is 40,000. In Scope mode, the maximum number of averages is equal to 8,231,936 divided by data points.

⁷ Averaging resolution of 0.001 dB is not available with the NI-568x SFP. This feature is only available when using the NI-568x instrument driver. Averaging resolution is defined as the place after the decimal to which the reading becomes stable.

⁸ Times based on benchmark results. Performance may vary based on your system.

⁹ Times based on benchmark results. Performance may vary based on your system. Formula assumes averaging is set to 1, and trigger source is set to Immediate.

¹⁰ The start exclusion time plus the end exclusion time must be less than the slot width.

¹¹ Software trigger not available in the NI-568x SFP. This feature is only available when using the NI-568x instrument driver. Internal and external triggers are not available when using Continuous acquisition mode.

¹² The external trigger source is sampled approximately every 7.5 μs.

¹³ Tested in accordance with MIL-PRF-28800F (Class 3).