From Ettus Knowledge Base
Application Note Number
AN-881
Revision History
Date Author Details -05-01 Neel Pandeya
Abstract
This AN explores the USRP family at a high level, compares devices across several primary features, and walks the reader through the process of selecting a particular device for the their application.
USRP Product Selector
The USRP Product Selector will help you choose the Ettus Research USRP Software Defined Radio products that are the best fit for your application. Based on your answers to a series of questions, the USRP Product Selector will generate a PDF price quote and it to you. The Ettus Research sales team may follow up with you to answer any additional questions that you might have. If you would like a person to talk you through the USRP product selection process, please send an to .
Overview
This guide is provided by Ettus Research to help users select the most appropriate Universal Software Radio Peripheral (USRP&#;) for their specific application. In order to make the selection process as straightforward as possible, a table showing various features is provided as a basis for the selection process.
Understanding DSP Fundamentals
If you are new to the USRP family of products, software defined radio, or digital signal processing in general, it may be useful to perform some simulation of the signals you wish to manipulate before selecting USRP hardware. Simulating signals and algorithms in software frameworks such as GNU Radio or LabVIEW will ensure a proper understanding of various concepts, such as Nyquist theorem, ADC/DAC and limitations, for example. Understanding the basics of signal theory and digital signal processing is the first step towards understanding how to make the best use of an appropriate USRP model. The Suggested Reading page provides access to several resources that may be helpful in understanding the basics.
Common Applications
Table 1 shows USRP/daughterboard combinations commonly used in various application areas. While Table 1 can serve as a starting point for selecting a USRP device, Ettus Research recommends new users evaluate their application requirements against the specifications of the USRP devices. sections of this document will assist in the selection process.
USRP Device Characteristics
Table 2 shows the key characteristics of all USRP models available from Ettus Research. The table is useful for determining the interface type, bandwidth capabilities, and synchronization mechanisms specified for each USRP model. You can use this information, and the requirements for the application in question, to select a USRP radio.
10 GigE
153.6, 125, 122.88 2 16 153.6, 125, 122.88 14 153.6, 125, 122.88 Yes Yes Yes N310 1 GigE10 GigE
153.6, 125, 122.88 2 16 153.6, 125, 122.88 14 153.6, 125, 122.88 Yes Yes Yes B200mini USB 3.0 61.44 N/A 12 61.44 12 61.44 No No Yes B205mini USB 3.0 61.44 N/A 12 61.44 12 61.44 No No Yes B200 USB 3.0 61.44 N/A 12 61.44 12 61.44 No Yes Yes B210 USB 3.0 61.44 N/A 12 61.44 12 61.44 Yes Yes Yes X300 USB 3.01 GigE
10 GigE
PCIe
200 2 14 200 16 800 Yes Yes Yes X310 USB 3.01 GigE
10 GigE
PCIe
200 2 14 200 16 800 Yes Yes Yes E310 Embedded 61.44 N/A 12 61.44 12 61.44 Yes No Yes E312 Embedded 61.44 N/A 12 61.44 12 61.44 Yes No Yes E320 Embedded1 GigE
10 GigE
61.44 N/A 12 61.44 12 61.44 Yes Yes Yes Table 2 - USRP Characteristics by Model
The following sections cover frequently asked questions in choosing a USRP device that&#;s right for your application.
Do I want to perform processing on a host PC, or operate the USRP device in a standalone fashion?
This is an obvious differentiator of the USRP Embedded Series. If you need the USRP to operate a USRP radio without a host PC, the USRP E310/E312/E320 is the most appropriate. The USRP E310/E312/E320 is ideal for applications that might require mobile transceivers or distributed RF sensors. Unless the user has a clear requirement for embedded operation, Ettus Research recommends the USRP N200, N210, B200, B210, X300, X310, N300 or N310. Developing with a host-based platform typically involves less risk and will require less effort to optimize various pieces of the software radio.
In many cases it may be easier to develop with a USRP B200/B210 or USRP N200/N210, then port the code to the USRP E310/E312/E320. The UHD (USRP Hardware Driver) enables this portability. You must also consider the different processing capabilities of the host machine and ARM processor used on the USRP E310/E312/E320.
Do I Need Synchronization and/or MIMO Capability?
Table 3 summarizes the synchronization features of each USRP device. Table 4 shows recommended solutions for MIMO systems of various sizes.
If you need MIMO capability for your application, Ettus Research recommends the USRP N200/N210, X300/X310, N300/N310 or E320. These units can be synchronized by providing a common time and frequency reference. Two USRP N200/N210s can be synchronized for MIMO operation with an Ettus Research MIMO cable. Alternatively, external 10 MHz reference and 1 PPS signals can be distributed to multiple USRP radios. With proper consideration for interface issues, it is possible to create MIMO system of arbitrary size with the USRP N200/N210, X300/X310, N300/N310 and E320.
The USRP B210, N300, E310/E312/E320 can serve a 2x2 MIMO capability because it has two integrated RF channels. When using the USRP B210 the available bandwidth is limited dependent upon the USB controller, and selected MIMO configuration. The USRP E310/E312's streaming bandwidth is limited to the 1 GigE interface to the ARM CPU. The USRP E320 supports streaming at full rate of 61.44 MS/s (SISO) or 30.72 MS/s (MIMO) via the 10 Gb interface. The USRP N300 supports streaming at 153.6 MS/s (SISO) and 125 MS/s (MIMO) via the 10Gb interface.
What Are My Bandwidth Requirements?
Many Bandwidth requirements can also be used to narrow down the USRP selection. As seen in the table, the USRP N200/N210 is capable of streaming up to 50 MS/s in each direction in 8-bit mode, and 25 MS/s in 16-bit mode. The USRP B200 is capable of streaming up to 61.44MS/s total in 16-bit, 12-bit or 8-bit modes. The USRP E320 is capable of streaming up to 61.44 MS/s in 16-bit mode. The X300/X310 is capable of streaming up to 200 MS/s per channel (400 MS/s total) with 160 MHz of usable bandwidth per channel. The N300/N310 is capable of streaming up 122.88, 125 or 153.6 MS/s per channel. The N300/N310 is limited to 2x2 operation when using a 153.6 MS/s sample rate.
However, if there is interest in transmit and/or receiving larger bandwidth signals such as 802.11, the USRP N200/N210, X300/X310, N300/N310 or E320 would be appropriate. Note these limitations are based on the data throughput provided by the corresponding interfaces. It is important to consider the performance of the processing platform, and the computational intensity of the application. The constraints of the processing platform are independent of the full capability of the Ettus Research USRP radio and UHD.
What interface do I prefer to work with?
Assuming you have narrowed the viable devices down based on bandwidth, MIMO and channel count requirements, it is possible to select a USRP device based on the interface.
In general, USB 3.0 ports are more plentiful on computers. This makes the USRP B200/B210/B200mini/B205mini slightly more usable at short ranges. The USRP N200/N210 requires a Gigabit Ethernet port and a PC typically only provides one such port. If internet access is required, the user will also need to plan for an additional network adapter. The USRP X300/X310, N300/N310 and USRP E320 all support streaming via either a 1 GigE or 10 GigE interface.
The Gigabit Ethernet interface of the USRP N200/N210 can operate over significantly longer ranges (typically up to 100ft) compared to the USB interface of the USRP B2xx. This makes it possible to operate the USRP radio it more remote locations further from the host computer. The GigE interface can be accessed via a Gigabit Ethernet switch, allowing access to multiple devices. However, Ettus Research recommends a homogeneous network without other devices, such as network routers attached.
The 10 Gigabit Ethernet interfaces of the USRP N300/N310, X300/X310 and E320 can be operated using multimode fiber optic cables with appropriate adapters which increases the distance from the host computer.
Will I develop custom IP for the USRP device&#;s FPGA?
While most users deploy their USRP devices in a stock configuration, many others customize the FPGA with their own functionality. For example, you may want to offload modulation, demodulation, or other PHY/ MAC operations to the FPGA. This reduces host processing requirements, and may allow data reduction before passing data over the host interface. A summary of the FPGAs used on each USRP model are shown in Table 5.
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Model FPGA Vendor FPGA Series FPGA Part Number System Gates Logic Elements Logic Cells Slices DSP48's BRAM DCM's Free Tools? N200 Xilinx Spartan 3A DSP XC3SDA k - 37,440 16,640 84 260k 8 Yes N210 Xilinx Spartan 3A DSP XC3SDA k - 53,714 23,872 126 373k 8 No B200mini Xilinx Spartan-6 XC6SLX75 - - 74,637 93,296 132 3,096k 12 Yes B205mini Xilinx Spartan-6 XC6SLX150 - - 147,443 184,304 180 4,824k 12 No B200 Xilinx Spartan 6 XC6SLX75 - - 74,637 93,296 132 3,096k 12 Yes B210 Xilinx Spartan 6 XC6SLX150 - - 147,443 184,304 180 4,824k 12 No X300 Xilinx Kintex-7 XC7K325T - - 321k 407,600 840 16,020k - No X310 Xilinx Kintex-7 XC7K410T - - 406k 508,400 28,620k - No E310 Xilinx Zynq- XC7Z020 - - 85k 106,400 220 560k - Yes E312 Xilinx Zynq- XC7Z020 - - 85k 106,400 220 560k - Yes E320 Xilinx Zynq- XC7Z045 - - 350k 437,200 900 19.2 Mb - No N300 Xilinx Zynq- XC7Z035 - - 275k 343,800 900 17.6 Mb - No N310 Xilinx Zynq- XC7Z100 - - 444K 554,800 26.5 Mb - No Table 5 - FPGA Resources
The USRP N200 and USRP N210 are great, generic platforms to experiment with FPGA development. However, the important difference between these two is the FPGA size, and requirements for Xilinx development tools. The USRP N200 includes a Xilinx Spartan XC3SDA FPGA. This FPGA is optimized for DSP capability, and the logic can be modified with free Xilinx ISE tools. The USRP N210 includes a Xilinx Spartan XC3DA FPGA. This FPGA provides nearly twice the resources, but requires a licensed seat of the Xilinx development tools for development.
Do I need flexible sample clock frequencies?
Some applications may benefit from a flexible sample clock frequency. The USRP E310/E312/E320 and USRP B200/B210/B200mini/B205mini include a flexible frequency clocking solution. This flexibility allows ideal sample clock frequencies to be used for various communications standards. For example, the GSM implementations commonly use a 52 MHz sample clock.
Do I want or need a rack-mountable solution?
Generally speaking, the selection of the USRP is based on performance requirements of the electrical components. However, the convenience of a rack-mounted solution may be an attractive feature that drives your decision. The USRP N200/N210, X300/X310 and N300/N310 can all be mounted in Ettus Research rack chassis. Up to four N200/N210 USRP devices can be mounted in the 3U chassis. Up to two X300/X310 or N300/N310 USRP devices can be mounted in the 1U chassis.
Will my requirements become more demanding as I learn more about the USRP and RF systems?
One final thing to consider is how your requirements will change over time. While a lower-cost USRP device, such as the USRP B200/B200mini, may meet your immediate requirements, it is possible that the USRP N200/N210, N300/N310 or E320 would be a more appropriate platform as you continue to develop more advanced RF systems. Key improvements to note in the higher-end USRP N200/N210/X300/X310/N300/N310/E320 is the increased bandwidth, increased dynamic range, and MIMO capability.
Fortunately, UHD allows the user to develop a single application compatible with all USRP models. Within certain limitations, the code you develop to work on a USRP B2xx will generally work on any other USRP. You must still consider variables such as sample rate, host interface bandwidth, and synchronization features to ensure compatibility.
Conclusion
This application note presents the functional specifications of each USRP device sold by Ettus Research. The data from this document can be used to make an educated selection of the most appropriate USRP device for a particular user or application. If you have any additional questions, do not hesitate to contact us at .
We've recently been testing methods to help budding amateur radio astronomers get into the hobby cheaply and easily. We have found that a low cost 2.4 GHz 100 cm x 60 cm parabolic WiFi grid antenna, combined with an RTL-SDR and LNA is sufficient to detect the hydrogen line peak and doppler shifts of the galactic plane. This means that you can create backyard hydrogen line radio telescope for less than US$200, with no complicated construction required.
If you don't know what the hydrogen line is, we'll explain it here. Hydrogen atoms randomly emit photons at a wavelength of 21cm (. MHz). Normally a single hydrogen atom will only very rarely emit a photon, but the galaxy and even empty space is filled with many hydrogen atoms, so the average effect is an observable RF power spike at ~. MHz. By pointing a radio telescope at the night sky and averaging the RF power over time, a power spike indicating the hydrogen line can be observed in a frequency spectrum plot. This can be used for some interesting experiments, for example you could measure the size and shape of our galaxy. Thicker areas of the galaxy will have more hydrogen and thus a larger spike, whereas the spike will be significantly smaller when pointing at empty space. You can also measure the rotational speed of our galaxy by noting the frequency doppler shift.
The 2.4 GHz parabolic WiFi grid dishes can be found for a cheap at US$49.99 on eBay and for around US$75 on Amazon. Outside of the USA they are typically carried by local wireless communications stores or the local eBay/Amazon equivalent. If you're buying one, be sure to get the 2.4 GHz version and NOT the 5 GHz version. If you can find 1.9 GHz parabolic grid dish, then this is also a good choice. Although we haven't tested it, this larger 2.4 GHz grid dish would probably also work and give slightly better results. WiFi grid antennas have been commonly used for GOES and GK-2A geosynchronous weather satellite reception at 2.4 GHz with RTL-SDRs as well and we have a tutorial on that available on our previous post.
These dishes are linearly polarized but that is okay as hydrogen line emissions are randomly polarized. Ideally we would have a dual polarization (NOT circular polarized) feed, but linear appears to be enough and is much simpler. In addition, the 2.4 GHz feed is obviously not designed for MHz, but just like with GOES at 1.7 GHz the SWR is low enough that it still works.
The animation below shows a hydrogen line "drift" scan performed with the 2.4 GHz WiFi dish, an RTL-SDR Blog V3 and a NooElec SAWBird H1 LNA. The scan is performed over one day, and we simply let the rotation of the earth allow the Milky Way to drift over the antenna. The Stellarium software on the left shows the movement of the Milky Way/galactic plane over the course of a day for our location. The dish antenna points straight up into the sky, and we have set Stellarium to look straight up too, so Stellarium sees exactly what our dish antenna is seeing.
You can clearly see that there is a lump in the radio spectrum at around .40 MHz that grows when parts of the Milky Way pass over the antenna. This lump is the hydrogen line being detected. As our Milky Way galaxy is filled with significantly more hydrogen than empty space, we see a larger lump when the antenna points at the Milky Way, and only a very small lump when it points away.
It's important to ignore the very narrowband spikes in the spectrum. These narrowband spikes are simply radio interference from electronics from neighbors - probably TVs or monitors as we note that most of the interference occurs during the day. There is also a large constant spike which appears to be an artifact of the LNA. The LNA we used has a MHz filter built in, but LCD TVs and other electronics in today's suburban environment spew noise all across the spectrum, even at MHz.
You can also note that the hydrogen line peak is moving around in frequency as different parts of the galaxy pass overhead. This indicates the doppler shift of the part of the galaxy being observed. Because the arms of the galaxy and the hydrogen in it is rotating at significant speeds, the frequency is doppler shifted relative to us.
Using the power and doppler shift data of the hydrogen line is how astronomers first determined the properties of our galaxy like shape, size and rotational speed. If we continued to scan the sky over a few months, we could eventually build up a full map of our galaxy, like what CCERA have done as explained in this previous post.
Total cost (not including the PC): US$179.40, and probably less if you already have some parts or find similar items priced cheaper elsewhere.
The recommended setup is simple. Antenna pointed straight up -> LNA -> RTL-SDR -> USB Cable -> PC.
Detailed instructions below:
It may also be wise to waterproof your LNA and RTL-SDR if kept outdoors. This can be as simple as putting it in a plastic bag, or old coke bottle sealed with some putty.
In order to detect the hydrogen line we need to use software capable of integrating/averaging many FFT samples over time. Averaging the samples reduces the SDRs quantization noise, allowing the weak hydrogen line peak to be seen. Because the galaxy is moving fairly slowly in the sky, we can safely average for 5-10 minutes at a time.
For Linux, there are various programs that can be used. PICTOR, and rtl-obs are some good choices, but are a little more complicated to set up. But they have some good features like the ability to properly calibrate the results, and some interesting algorithms that could increase the SNR of the hydrogen line detection.
For this tutorial we will keep it as simple as possible, and we will use Windows, with SDR# and a SDR# plugin called "IF Average". We will also use a free astronomy program called Stellarium for tracking the Milky Way's galactic plane across the sky.
By clicking on an object within the Milky Way or behind it, you can find out the Galactic coordinates of where in the Galaxy you are pointing. This could be useful for comparing with already known results like those shown here. Right click to remove the info text about that object.
You can download the SDR# Program with IF Average plugin preinstalled at this Dropbox link. This is provided by Dr Daniel Kaminski, author of the IF Average plugin. If you download this zip, simply unzip it to a folder on your PC and open SDRsharp.exe. If you complete this step, you can skip directly to step 4. Alternatively, start from step 1 and download and install SDR# and the IF Average Plugin manually.
Download the IF average plugin. Daniel's GitHub contains the latest files.
To Download from GitHub, click the Green "Code" button, and the click "Download Zip"
Open the Zip file and go into the SDR_AVE_new-master\Release folder. Then copy the following files into your SDR# plugins folder from Daniel's Releases GitHub folder:
MonoGame.Framework.dll
SDRSharp.Average.dll
SharpDX.DXGI.dll
SharpDX.Direct3D11.dll
SharpDX.dll
Download and copy the following files from the main SDR_AVE_new-master folder into the main SDR# directory.
ft2.xnb
NOTE: If the above is not working, you should try installing the plugin on an older version of SDR#. Older versions of SDR# can be downloaded from https://www.iz3mez.it/software/SDRSharp. We tested the old plugin with SDRSharp v and it worked well.
For older version of SDR# Daniel's website contains the older version here (called AVE for SDR#).
Alternatively, if there is some problem with the plugin website, the older version of his plugin is still available on his Dropbox. Go to Download->Direct Download to download it to your PC. We have also decided to mirror the plugin here on the blog server just in case the Dropbox file goes offline. You will need to use an older version of SDR# for these files.
At this stage, you now need to wait for the Milky Way to enter your antennas beamwidth and watch for the H-line peak. The software will continually average the spectrum.
If you want to create a timelapse like the gif shown at the top of the post we can recommend a program called "Chronolapse", which takes a screenshot every X minutes. You can then convert those images into a movie or gif. The IF average plugin can also output data files which could be used for further analysis.
If you do not do the calibration at all, your spectrum will appear quite wavy. Be sure to not confuse those waves with the hydrogen line peak.
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