Design Con 2015

Product review: Rigol DSA815TG spectrum analyzer

-October 19, 2012

If there's been one spectrum analyzer that's created buzz lately, it's the recently announced Rigol DSA815 budget ($1,295) spectrum analyzer, which tunes from 9 kHz to 1.5 GHz. A tracking generator option will run an extra $200 and the EMI option, which provides quasi-peak detection and the three EMI bandwidths (and especially excites us EMC engineers), is an extra $600. There are a number of other options available. I was able to get my hands on a review unit and have put it through its paces during some recent EMC seminars and client projects.


Figure 1 - The Rigol DSA815TG (with tracking generator).

General
Upon opening the box, the first thing that struck me was the small size of the unit and the apparent quality of the enclosure and controls. There's no skimping there. It's no larger than some of the smaller-size budget oscilloscopes with dimensions of 14" wide by 7" tall by just 5" deep. This is one compact spectrum analyzer!

The second thing that struck me was the weight of the unit for its size at 9.4 pounds. Obviously, there's some shielding inside. One minor thing I couldn’t help noticing was that the carry handle, while mounted with metal pins (comforting), wasn’t mounted at the center of mass, so the unit tilts slightly forward when carried.

The carry case is well made and nicely padded, but was originally designed for their 1000-series oscilloscopes, so it's a very tight fit for the wider analyzer and the “hold-down” straps don’t fit all the way across the top. I also noticed (painfully) the front snap-clips that hold the cover closed will pinch your fingers, if held on the sides while snapping them closed. Better to grasp it front and rear. The front pouch is large enough to carry an assortment of cables and adapters and the rear compartment fits the line cord nicely. I do love the rounded “lunchbox” style case. It rather reminds me of the old-time doctor’s kits when they used to make house calls. Yes, I am that old! I’m hoping Rigol will supply us a proper case in the future.

The Quick Guide brochure explained how to adjust the front legs, connect it to power, do an initial self-calibration, and the layout of the controls and ports, but little else. However, the actual user guide is supplied on CD or available as a download from their web site. I added the guide to my iPad for easy reference.

Even better, the table of contents and index are all hot-linked to their corresponding sections of the user guide. The “key points” throughout the manual were welcome aids to my understanding.

The controls are arranged in logical groupings, duplicating to a large degree those found on Agilent spectrum analyzers. Besides the usual frequency, span and amplitude buttons, major groupings include control, marker, measure, utility and Edit (numeric and text input). I loved the large color screen (800x480 WVGA). It was clear and easily readable. A vertical row of soft-keys are used to select secondary functions. Down along the left side of the display you'll find a column of analyzer status icons. There's also a "Help" key that will describe each control for you. The most used controls are all one or two button-presses away.

There is a USB-B 2.0 port on the front and USB-A 2.0 (printer) and Ethernet (10/100 Base-T) ports on the rear. In addition, there are rear BNC ports for Trigger In, 10 MHz Out and 10 MHz In. It also includes a Kensington® security slot. The line power is universal and can take 100 to 240 VAC at 45 to 440 Hz.

Specifications
Major "banner" specs include:
•    All digital IF technology
•    LXI compliant
•    9 kHz to 1.5 GHz frequency range
•    Up to -135 dBm displayed average noise level (DANL)
•    Resolution bandwidth (100 Hz to 1 MHz at -3 dB)
•    Video bandwidth (1 Hz to 3 MHz at -3 dB)
•    -80 dBc/Hz at 10 kHz offset phase noise
•    Total amplitude uncertainty of <1.5 dB
•    100 Hz minimum resolution bandwidth
•    1.5 GHz tracking generator option (-20 to 0 dBm)
•    EMI filter and quasi-peak detector option (200 Hz, 120 kHz and 1 MHz BWs at -6 dB)
•    VSWR measurement kit option (1 MHz to 2 GHz)
•    Connectivity: LAN (LXI standard), USB host, USB device, GPIB (option)
•    8-inch WVGA (800x480) display (600 pixel waveform resolution)
•    Advanced Measurement kit (option)
•    Ultra Spectrum (PC) software option (provides additional analysis, including a waterfall display)

I compared some of the most important DSA815 specs with Agilent Technologies most comparable analyzer (but at 10X the cost) - the model N9000A CXA (9 kHz to 3 GHz). In all cases, I tried to compare specs for the Agilent up to an upper frequency of 1.5 GHz. As you can see, the Agilent beat the Rigol technically (as expected) in all areas.

Table 1 – Comparison of the Rigol DSA815 with the Agilent N9000A CXA analyzer.

Boot-up time is just 17 seconds, much faster than Windows-based instruments. The cooling fan is audible but not distracting.

Detectors
The DSA815 has a number of detectors. These include positive peak, negative peak, sample, normal (the default), RMS average, voltage average and quasi-peak (optional). The quasi-peak detector is described more fully in the EMI option below. Rigol has a downloadable app-note describing the purpose of each in more detail.


Although advertised at "up to -135 dBm displayed average noise level (DANL)", in practical use, it was more on the order of -60 to -90 dBm, depending on the frequency span and resolution bandwidths invoked.

File and Screen Captures
It's relatively easy to save screen captures and save/recall instrument setups. The method for naming files is somewhat like entering text on regular (non-"smart") mobile phones and is fairly quick once you get the hang of it. It would be nice to be able to plug in a keyboard for that purpose, though. One other improvement might be to define the local language in an overall user setup. This would avoid having to rotate through English and Chinese mode every time you went to enter a file name. To save screen captures (.bmp format), plug in a memory stick to the front USB port and press the “Print” button on the left side of the display. Instrument setups and screen captures may be saved to either an external memory stick or internal memory. There are six user-defined front panel instrument presets, in addition to the unlimited ones saved to memory.

>>Hands On Testing: Putting it through its Paces
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