Constant Wave

2-D Visualization of S-Parameters

2011-03-22T07:46:00.002-06:00

Visualizing s-parameters in the joint time-frequency domain is extremely powerful. For example, here is some S11 data that shows an initial reflection from a connector and then another reflection from the DUT:

While typical time domain software will only show a trace at a single frequency (many engineers do not know this, and do not know which frequency is selected), Spectro VNA LIte allows the engineer to select different frequencies to view (just by clicking directly on the plot). This is important so that they can see the response at their operating frequencies, rather than one selected by the VNA software.

At 20.97 GHz, the S11 of the connector is greater than the S11 of the DUT:

At 15.13 GHz, the situation is reversed. Now the S11 of the DUT is higher:

At 3.25 GHz, S11 remains below -20 dB for the entire plot:

As seen above, the reflections are very different at different frequencies.

The Real Goal of Visual Thinking

2011-03-14T10:03:00.000-06:00

In Dan Roam's excellent book The Back of the Napkin: Solving Problems and Selling Ideas with Pictures, he states that "The real goal of visual thinking is to make the complex understandable by making it visible--not by making it simple."

This is precisely the point of the visual workspaces in Constant Wave's software for vector network analyzers, vector signal analyzers, and oscilloscopes. Communication standards and devices are increasing in complexity. Masking this complexity via over simplification does not help engineers. Making the complex understandable does.

For example, according to Wikipedia, a Zadoff-Chu sequence is defined as:

The complex value at each position (n) of each root Zadoff–Chu sequence (u) given by






The Zadoff-Chu sequence stands out in the following LTE signal, captured using Spectro VSA:

The image shows that the Zadoff-Chu sequence is a series of tones sweeping the bandwidth of the signal, thereby making a complicated mathematical formula understandable.

Is Your Vector Network Analyzer Lying To You?

2011-02-27T12:09:00.000-07:00

The following image depicts a typical time domain plot from a vector network analyzer (VNA):

This plot shows the magnitude of S11 as a function of time, but at what frequency? All frequencies? Your frequency?

The answer is that it represents S11 at a single frequency. The frequency chosen depends on the VNA and the type of time domain processing performed. If that frequency is the frequency that you are interested in, then you are in luck.

But what if you need to understand the behavior of your system at a different frequency? Or multiple frequencies?

As shown in the following image, Spectro VNA from Constant Wave allows you to see S-parameters as a function of both time and frequency simultaneously. The color represents magnitude, where red is a higher magnitude and blue is lower.

While much insight can be gained from viewing this plot, it is also a workspace, where specific values can be determined with a click of the mouse. One may also select individual frequencies to see a traditional time domain plot at a frequency of interest, instead of the frequency chosen by the VNA.

So, while your VNA with traditional time domain processing isn't lying to you, it isn't telling you the whole truth either.

FCC Launches Remake Of Radio Spectrum Technology

2010-12-10T16:28:00.001-07:00

Interesting post over at CommLawBlog: FCC Launches Remake Of Radio Spectrum Technology

As more and more users are packed into the same bandwidth, the demand for joint time-frequency domain processing will continue to increase. Spectrograms are useful for finding open space, detecting and identifying interference, and monitoring your own signals to ensure that they don't interfere with others.

The Sweet Spot for Mobile Broadband

2010-09-30T11:54:00.000-06:00

According to The Great Radio Spectrum Famine in the IEEE Spectrum magazine, the sweet spot for mobile broadband is 300 MHz to 3500 MHz:

Every application of radio works best within a certain range of frequencies, and mobile broadband is no exception. Its sweet spot is relatively narrow, roughly in the range of 300 to 3500 megahertz. That's because radio waves that are much above 3500 MHz (shorter than about 9 centimeters) do not penetrate well into buildings or through rugged terrain, leading to frustrating dead spots. Lower frequencies are better in this regard, but they require awkwardly large antennas for efficient transmission; 300 MHz is roughly the lowest frequency compatible with a reasonably efficient antenna that's small enough to fit in a handheld device.

Joint Time-Frequency Domain for Vector Network Analyzers

2010-09-29T18:07:00.001-06:00

Our unique spectrographic analysis allows engineers to see the characteristics of reflections in both time and frequency simultaneously. Standard VNA software shows magnitude as a function of frequency, but includes all reflections. Traditional time domain packages show individual reflections, but obscure what is happening in the frequency domain.

In this image of the joint time-frequency domain, time is displayed along the x-axis and frequency is displayed along the y-axis. The color indicates the magnitude of S11, with warmer colors indicating higher magnitude (red and orange) and cooler colors indicating lower magnitude (blue, purple, and black). The expected reflection occurs at 4 ns. It can be readily determined from the image that the magnitude of S11 is increasing with frequency for all of the reflections.

A discontinuity is generating a reflection at 2 ns. The effect of this discontinuity can be removed using Time Domain Substitution.

Time Domain Substitution

2010-09-28T12:33:00.000-06:00

Time Domain Substitution makes it easy to calibrate vector network analyzers (VNAs) where they need to be calibrated--near the device under test. Most VNAs can be easily calibrated at the ends of coaxial cables using automated calibrators. But in today’s world, many measurements must be made beyond the reach of coaxial cables. Making calibration easier, but at the wrong reference plane, is not an acceptable solution. Post-processing methods, such as port extension and frequency gated by time, are only approximate solutions.

The patent pending technology of Time Domain Substitution allows the user to set the reference plane by merely creating a temporary short circuit at the desired location. No expensive custom calibration standards are required.

Time Domain Substitution is available in Spectro VNA™ Vector Network Analyzer software and Spectro TDS™ Toolkit.

What is a Spectrogram?

2009-10-22T13:00:00.000-06:00

A spectrogram displays the power of a signal as a function of both time and frequency simultaneously. Many engineers are familiar with time domain (power vs. time) and frequency domain (power vs. frequency) plots. While somewhat useful, each plot only tells half the story. A time domain plot will tell you "when" something happened, but it won't tell you "what" happened. A frequency domain plot will tell you "what" the signal looks like, but it won't tell you when it occurred. In order to see the full picture, what is happening and when it is happening, it is necessary to view the signal in joint time-frequency space, i.e., a spectrogram. For more information, please visit our web site.

Constant Wave Publishes LTE Waveform Generation Source Code

2009-10-12T06:52:00.000-06:00

COLORADO SPRINGS – October 9, 2009 – Constant Wave, a developer of innovative RF signal processing software, has published source code for LTE waveform generation on its web site at http://www.ConstantWave.com/lte_source_code.aspx . Releasing C++ source code to the public domain can simplify the implementation of this challenging standard. In addition, it allows users of Constant Wave’s Spectro LTE Gen software to examine the core algorithms that construct LTE signals. This is a key issue for standards which are still evolving, such as LTE.
Although users of the source code are encouraged to submit comments and improvements to Constant Wave, they are under no obligation to do so. The source code is being released to the public domain, so users are free to use and modify the code as they wish with no requirements for attribution or republishing, as is common with open source licensing.

Some users only want algorithms; others need a complete solution
While the release of source code used in proprietary software is not common, it addresses the requirements of two distinct groups. “Some users only want algorithms; others need a complete solution”, explains Dr. Don Metzger, Chief Technology Officer for Constant Wave. “Both groups are served by releasing source code. Those interested in algorithms get a working code base which they can modify as desired. Those interested in a complete solution get visibility into the implementation of LTE. These users need software that can interface with hardware, work with multiple file formats and display the results of their work, requirements met with Spectro LTE Gen.”

Capabilities
Both the source code being released, and Constant Wave’s complete solution, Spectro LTE Gen, create LTE uplink (PUSCH) waveforms for use in testing LTE compliant devices and systems. They include support for 1.4, 3, 5, 10, 15, and 20 MHz bandwidths and both normal and extended cyclic prefixes. QPSK, 16-QAM, and 64-QAM modulations are supported.
To help users better characterize their devices, Spectro LTE Gen can create modified signals that exhibit desired properties. Users may apply pulse shaping to limit the frequency spectrum, add time and frequency offsets, add broadband noise, and adjust the output sample rate.
In addition to generating waveforms, Spectro LTE Gen allows users to see the EVM and symbol constellation for the generated data, create waveforms with known values of EVM, and view the waveforms in the joint time-frequency space with Constant Wave’s high definition spectrogram display.

Software as a Service (SaaS)
Spectro LTE Gen software is available on the Constant Wave web site using the Software as a Service (SaaS) model. SaaS allows users to rent the software on a monthly subscription basis at a price far below the standard purchase price. The SaaS model allows users to fit their expense to their need. They can avoid the expense of a perpetual license, a particularly desirable feature if the duration or quantity of licenses is varied or uncertain. Consultants working on short projects can benefit from this model, as can production environments where demand can ramp up and down quickly. Purchasing departments appreciate the fact that they can tailor their payments to fit their financial situation: capitalization or expense, lump sum or pay as you go.

About Constant Wave
Constant Wave is a developer of innovative RF signal processing software using the Software as a Service (SaaS) model. Other products include Spectro VNA, which introduced the biggest advance in time domain processing for vector network analyzers in 20 years, Spectro VSA, and Spectro Scope. The common theme in all of the products is to help engineers visualize their signals so that they can be more effective. As communication standards continue to evolve, traditional methods of analyzing data make it easy to miss important information in a captured signal. Additional information about Constant Wave, including white papers and product briefs, can be found at http://www.constantwave.com .

New White Paper Available

2008-10-17T00:51:00.000-06:00

A new white paper on Spectro VSA titled "Using Spectrograms to Find Signal Anomalies" is now available on the web site on the white papers page and the Spectro VSA page.

1.5.14.0 Now Available

2008-10-15T22:10:00.001-06:00

This update offers Agilent ENA compatibility for Spectro VNA. It also adds the feature of remembering the LAN settings for communications with instruments for both Spectro VNA and Spectro VSA.

1.5.13.0 Now Available

2008-10-15T22:08:00.000-06:00

This version adds the “Axes Limits” dialog to all 2D plots. This dialog can be accessed by right clicking on a plot and choosing “Axes Limits…” from the context menu.

Spectro VSA is now in beta!

2008-10-10T10:42:00.000-06:00

If you would like to help beta test Spectro VSA, please email us at concierge@constantwave.com for a free trial activation code.

1.5.12.0 Now Available

2008-10-05T17:36:00.000-06:00

There is a new version of VSA on the website, 1.5.12. We added units buttons to the Pre-processing dialog for the skip, limit, pre-pend and append items. These are a new type of units button which cycle through points and time. This allows the user to choose those items either in terms of time units or points.

1.5.11.0 Now Available

2008-10-01T09:57:00.000-06:00

Version 1.5.11.0 of Spectro VSA and Spectro VNA is now available for download on the web site. The verification data provided upon program start has been expanded.

1.5.10.0 Now Available

2008-10-01T09:56:00.000-06:00

Version 1.5.10.0 of Spectro VSA and Spectro VNA is now available for download on the web site. Both programs now provide information on when your current subscription will expire and how long your grace period lasts. As always, if you have any questions, please contact us at concierge@constantwave.com.