N6831A VLF-HF Wideband Receiver

Digital Wideband Acquisition System

Background

Keysight has a significant history in the development of HF receivers, delivering the industry’s firstever revolutionary digital wideband HF acquisition system in the late 1990s. The HP (and following Agilent) E3238S system came to market at that time with a proprietary 23-bit analog-to-digital converter (ADC) coupled with a unique software solution providing users with a comprehensive signals development capability that required no coding. These systems saw use globally in many settings and applications and were used extensively to fill gaps in the capabilities of existing systems operating in various regions of the world.

Keysight’s new HF receiver provides benefits in size, weight, and power, and includes the features of the original N6830A VXI receiver module, along with some key enhancements. Further, E3238S users made significant investments in the software (in terms of funding), and in the development of signal detectors (in terms of time and effort). This new receiver provides a path forward for those users, offering software and hardware updates that make the most of what has already been invested.

General Description

The N6831A receiver will communicate with the N6820ES Surveyor 4D software on a VITA-49 streaming interface, also making it compatible with other software packages capable of processing that form of data.  It will need to be paired with an appropriate server to support the applications. The built-in GPS receiver (L1) provides frequency and time references for accurate time stamping to support precision timedependent applications.

This receiver is designed to process the full VLF-HF band (9 kHz to 32 MHz) with 16-bit resolution making use of a 1-million-point FFT for remarkable speed and resolution. Several thoughtfully placed preselection filters optimize the sensitivity and integrity of the spectral content. The user manually controls these filters.  Additionally, 128 DDC channels provide a robust narrowband signal processing capability to classify signal candidates, make recordings, tip, and source data to other systems.

An important design goal was to match the sampling rates of the N6830A VXI receiver to make previously created USD (Universal Signal Detector) wideband detectors work properly with the new N6831A hardware. This detail may save significant effort in updating existing E3238S systems. Another important design goal was to satisfy the frequency ranges called out in Recommendation ITU-R SM.377 and 378 for frequency and bandwidth measurement in the VLF through HF spectrums.

As shown in Figure 1, the system has two basic inputs – the HF antenna, and the GPS antenna. The 10 MHz and 1PPS references on the HF receiver can come from either the embedded GPS receiver or from external references. There are two network connections between the HF receiver and the measurement server – the Gigabit Ethernet carries command and control, and the high-speed SFP+ connection carries the data output, including FFT spectral, and DDC narrowband streaming data. The interfaces are compliant with VITA 49.2.

Specifications

This section lists the specifications and supplemental information that applies to the N6831A HF receiver. The measurement hardware consists of a 1U standard rack-mounted unit. The specifications are based on 10 separate tests on 10 different units at room temperature.

VITA-49 Radio Access (VRA)

The N6831A is controlled through a comprehensive API referred to as the VITA Radio Access (VRA). The purchase of the receiver includes the VRA.