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First impressions - Rigol DSA815TG spectrum analyzer

-July 06, 2012

If there’s been one spectrum analyzer that’s created buzz lately, it’s the Rigol DDSA815 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 am putting it through it’s paces in the next couple weeks. However, with all the discussion of this product lately, I thought I’d give a few first impressions.

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The Rigol DSA815TG (with tracking generator). Photo, courtesy, Rigol Electronics.

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 hit me was the weight of the unit for it’s size at 9.4 pounds. Obviously, there’s some shielding inside. The carry case is well made and nicely padded, but was originally designed for their oscilloscopes, so it’s a very tight fit for the wider analyzer width-wise. 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.

I loved the large color screen (800×480 WVGA). It was clear and easily readable. The controls are arranged in logical groupings, duplicating to a large degree that 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). A vertical row of soft keys select secondary functions. Down along the left side you’ll find a column of analyzer status icons. There’s also a “Help” key that will describe each control for you.

Major “banner” specs include:

  • All digital IF technology
  • 9 kHz to 1.5 GHz frequency range
  • Up to -135 dBm displayed average noise level (DANL)
  • Resolution bandwidth (100 Hz to 1 MHz)
  • -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)
  • VSWR measurement kit option (1 MHz to 2 GHz)
  • Connectivity: LAN (LXI standard), USB host, USB device, GPIB (option)
  • 8-inch WVGA (800×480) display
  • Advanced Measurement kit (option)
  • Ultra Spectrum (PC) software option (provides additional analysis, including a waterfall display)

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The DSA815 can automatically display the top ten emission peaks. Photo courtesy Rigol Electronics.

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. The most used controls are all one or two button-presses away.

The Advanced Measurement Kit is interesting in that it adds the following automated measurements: channel power, noise marker, N dB bandwidth, emission bandwidth, occupied bandwidth, third order intercept distortion, a frequency counter, harmonic distortion, carrier to noise ratio, time domain power and adjacent channel power.

It’s 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. It would be nice to be able to plug in a keyboard for that purpose, though.

I had a chance yesterday to use the analyzer for some actual troubleshooting at a local test house here in Colorado. I was evaluating a small bare-board CPU and some associated “wall wart” power supplies for radiated and conducted emissions. It was wonderful to be able to tune down to 9 kHz for assessing conducted emissions - something I can’t readily do with my Thurlby Thander PSA2701T analyzer. I connected the Rigol analyzer to a Solar 9252-50-R-24-BNC LISN, tuned the it to the first power supply harmonic of 247 kHz, narrowed the resolution bandwidth to 300 Hz (best I could do without the EMI option, which is coming in a few days) and there was a clear picture of the emission. From there, I could try different line filter topologies while monitoring the improvements. Once I determined the most cost-effective filter design, we took the power supply from failing miserably to passing handily in just a couple hours - a much longer task without the use of a portable analyzer.

One feature I use a lot is the display line and by setting it on the baseline emission reading, you can then proceed to try various fixes while monitoring your progress. Unfortunately, it’s somewhat buried in the menu structure. I tried a couple types of current probes and got a reasonably high signal of the USB and power supply cables. The built-in broadband preamp works well to bring signals out of the noise level and for most of my troubleshooting measurements, I left it on. I also like the fact you can easily change from dBm to dBuv (and several others). This setup (as well as about three dozen other settings) may be preserved by saving the instrument state with a user-definable preset.

One way I evaluate a user interface is whether I need to refer to the user manual, and for the most part, the Rigol DSA815 met the challenge. The only time I had to dip into the manual was to learn how to save screen captures to a memory stick (you press the Print button). I’ve not yet had a chance to use the tracking generator, but that will come with the full review in a couple weeks.

All in all, I was impressed with the quality, features and ease of use, and I haven’t even gotten to some of the good stuff yet!

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