Software-defined radios (SDRs) are multi-purpose devices with the potential to work with any electronic communication system. The technology was mainstreamed thanks to low-cost radio receivers and free open-source software. Today, users of embedded systems and single-board computers now have new options that are smaller and lighter than previous SDR generations.
As part of a new digital receiver project, I tested the Nooelec NESDR Nano 3 and the NESDR Nano 2+, which I purchased as part of Nooelec Inc.’s Stratux ADS-B Bundle.
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To recap, software-defined radios are modern alternatives to traditional hardware-based radios. Radio transmitters normally start with a fixed frequency (the carrier frequency) that will be slightly altered or modulated by an outgoing message. Radio receivers reverse this process through demodulation.
More info: What is Software Defined Radio? (Unboxing Tomorrow)
To support numerous modulation schemes, a hardware-based radio would need separate hardware sub-systems dedicated to each modulation type.
Software-defined radios side-step this problem by leaving the bulk of its signal processing to software. Consequentially, SDR devices have low component counts and yet have the potential to work with any type of modulation, encoding, or encryption.
RTL-SDR Chipset Features
The SDR chipset I have featured most often is the Realtek SDR (RTL-SDR). But loosely speaking, RTL-SDR is a class of USB-based SDR receivers produced by many manufacturers other than Realtek.
The rtl-sdr moniker can also refer to a free, open-source software package for Linux; which is usually printed in lowercase. Among other things, rtl-sdr includes the test application: rtl_test and other utilities that are optimized for most RTL-SDR receivers on the market.
Generic RTL-SDR Receivers dominated the market soon after 2012, but other manufacturers such as Nooelec Inc. began producing newer units with improved capabilities. According to the official Nooelec website, its smallest Nooelec SDRs (NESDRs) fall within its Nano series.
NESDR Nano 2+ vs. Nano 3 Comparison
The Nano 2 and Nano 2+ both have plastic enclosures, compared to aluminum for the Nano 3. And the Nano 2+ and Nano 3 both have vastly improved stability over both the Nano 2 and the larger, generic variety.
Using the rtl_test utility, you can easily characterize your system by entering “rtl_test” in the terminal…
This test revealed one of the NESDR’s biggest advantages: unique serial numbers.
The generic RTL-SDR style can use arbitrary serial numbers. Devices become indistinguishable if they share common serial numbers like “00000000” or “00000001.” You can re-assign the serial number using rtl_eeprom, however doing so incorrectly may render your device unusable. The NESDR series avoids this by assigning unique values that require no such adjustment.
Affiliate: This project was made possible thanks to TorGuard Online Privacy Protection Services.
Operationally, the greatest improvement over the generic RTL-SDR is the improved frequency stability. In normal operation, self-heating will cause the intended frequency to drift by up to 50 parts per million (ppm), or 50 Hz/MHz. The Nano 2+ and Nano 3 use temperature-compensated crystal oscillators (TXCOs) that are self-accurized to 0.5 Hz/MHz or better. If you’re dealing with narrowband signals, this can make all the difference.
Table 1: Comparison: Generic RTL-SDR vs. NESDR Nano 2+ vs. NESDR Nano 3
| Generic RTL-SDR | NESDR Nano 2+ | NESDR Nano 3 | |
| Demodulator | Generic RTL2832U OEM | Generic RTL2832U OEM | Generic RTL2832U |
| Tuner | Rafael Micro R820T | Rafael Micro R820T | Rafael Micro R820T |
| Tuner IC | R820T2 | R820T2 | R820T2 |
| Range (approximate) | 25 MHz to 1700 MHz | 25 MHz to 1700 MHz | 25 MHz to 1700 MHz |
| Antenna Connector | PAL | MCX, female | MCX, female |
| Connector Impedance | 75 Ω | 50 Ω | 50 Ω |
| Gain Setting (min) | +0 dB | +0 dB | +0 dB |
| Gain Setting (max) | +49.6 dB | +49.6 dB | +49.6 dB |
| Total Gain Levels | 29 | 29 | 29 |
| Timing Source | Quartz | TCXO | TCXO |
| Stability | ±50 PPM | ±0.5 PPM | ±0.5 PPM |
| Dimensions | 90 mm x 28 mm x 18 mm | 24mm x 21mm x 8mm | 17mm x 8mm x 20mm |
| ESD Suppression | *varies* | YES | YES |
| Enclosure Material | Plastic | Plastic | Aluminum |
Closing Remarks
The only difficulty I had with either unit was the female MCX antenna connector. My inventory favors the larger female subminiature type A (SMA) connector. Fortunately, this was a trivial matter, since the Nano 3 shipped with a right-angle male MCX to female SMA adapter, and the ADS-B kit included even more options. While these adapters do have a small amount of insertion loss, it was not noticeable during any of my projects here. Your application will probably not be affected unless you are hunting for very weak signals close to the receivers’ noise floor.
You should also know the Nano 3’s aluminum body acts as a heat sink for the internal radio amplifier. In a room temperature environment, my Nano 3 surface temperature was about 10 °C above ambient even when the system was not in use. The exact surface temperatures for various gain settings are included in Table 2 below. You should be prepared for higher temperatures if you operate at higher frequencies or in direct sunlight. The Nano 3 does come with an optional heatsink.
Table 2: NESDR Observed Surface Temperatures
| GAIN (dB) | SURFACE TEMPERATURE ° (C) |
| 0 | 32 |
| 22.9 | 44 |
| 49.6 | 47 |
Overall, the NESDR Nano 2+ and Nano 3 are probably my preferred platforms now for general-purpose SDR work below 1.7 GHz.
The Nano 3’s small size on a Raspberry Pi 4’s USB ports was a pleasant surprise that makes it slightly more desirable than others. And considering that each device had a unique serial number (something the generic RTL-SDR options often lack), these are an easy entry point for anyone needing to use multiple dongles at once.
References
| [1] | B. R. Mayes, “Unboxing the RTL-SDR.com Software Defined Radio,” Voxidyne Media, 10 Nov. 2019. [Online]. Available: https://unboxing-tomorrow.com/unboxing-the-rtl-sdr-com-software-defined-radio/. [Accessed 10 July 2021]. |
| [2] | B. R. Mayes, “What is Software Defined Radio?,” Voxidyne Media, 2 Nov. 2019. [Online]. Available: https://unboxing-tomorrow.com/what-is-software-defined-radio/. [Accessed 10 July 2021]. |
| [3] | “NESDR Nano Series-Nooelec,” Nooelec, Inc., 5 Jan 2021. [Online]. Available: https://support.nooelec.com/hc/en-us/articles/360005889913-NESDR-Nano-Series. [Accessed 10 July 2021]. |
| [4] | Rafael Micro, “R820T High Performance Low Power Advanced Digital TV Silicon Tuner Datasheet – Preliminary Version,” Rafael Microelectronics, Inc., 2011. [Online]. Available: https://rtl-sdr.com/wp-content/uploads/2013/04/R820T_datasheet-Non_R-20111130_unlocked.pdf. [Accessed 10 July 2021]. |
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