Discovery Drive is an automatic antenna rotator that is designed to be used with our Discovery Dish product, as well as similarly sized antennas such as Wi-Fi grid and Yagi antennas.
Discovery Drive with Discovery Dish Mounted
A motorized rotator allows you to use a satellite dish or directional antenna to track and receive signals from polar orbiting satellites, which quickly move across the sky. It also lets you switch swiftly between geostationary satellites without manually realigning the dish.
Examples of polar-orbiting weather satellites that you can track include NOAA POES, METEOR-M2, METOP, and FENGYUN. Depending on your location, you may also have access to other interesting satellites that dump data over specific regions. Amateur radio operators can also use Discovery Drive to track amateur radio satellites with Yagi antennas.
Discovery Drive
Discovery Dish is designed to be easy to set up and use. Unlike many other rotators on the market, no external controllers are required. Discovery Drive has a built-in ESP32 controller, and control can be commanded over WiFi or serial from rotctl-compatible software such as SatDump, GPredict, and Look4Sat on Android.
Features and Specifications
Up to 125 kgcm (12.25 Nm) of torque
ESP32 control board
± 1.5° of accuracy
-360° to +360° Azimuth range, 0° - 90° elevation range
1.5 RPM Azimuth speed, 0.25 RPM elevation speed
12 V power input (either barrel jack or USB Type-C Power Delivery)
Wi-Fi connectivity with browser-based web UI
Serial over USB data connectivity or Wi-Fi data connectivity
Low power draw (< 10 W, can be powered with PoE+ supplies and still have power left over for powering a single board computer and RTL-SDR)
Robust worm gear-locked output drives
Direct rotctl compatibility over Wi-Fi (compatible with programs that implement the rotctl protocol, such as SatDump, GPredict, and Look4Sat on Android)
A recently published CVE (Common Vulnerabilities and Exposures) states that a software-defined radio can be used to remotely send a brake command signal to the End-Of-Train wirelessly linked control box.
Security researcher Neil Smith reported the vulnerability. Neil explains more in X, explicitly noting that he has been trying to get this published for 12 years and how no one from the American Association of Railroads (AAR) seems to consider this vulnerability a significant issue.
US trains use wireless RF communications devices, called "End-of-Train" (EoT) and "Head-of-Train" (HoT), to enable data communication between the head and end of the train. The two systems interface with the train's braking and control system, allowing the engineer to view information from both sides of the train, and command systems at ends of a long train instantaneously. Such signals can easily be received with an RTL-SDR and the softEOT decoder, or the PyEOT decoder.
The vulnerability stems from the fact that a software-defined radio can easily be used to replicate an EoT RF signal that can command braking. The signal could be transmitted over a long distance with an appropriate amplifier and antenna. Unexpected braking could cause derailment, amongst other problems.
As of right now, the vulnerability is still unpatched, but AAR have noted that they intend to replace the system with the 802.16t standard. However, in the X thread, Neil notes that this replacement won't be in place until 2027 in the best-case scenario.
Thank you to Lincoln Boggs (KF8DPW) for submitting his open source RTL-SDR Blog V3 shield footprint PCB design, which is available on GitHub.
This PCB serves as a bare-bones starter design that precisely matches the footprint of the RTL-SDR Blog V3, allowing you to develop custom addon boards. The current layout provides connections to GPIO, I2C, CLK, and several other pins on the RTL-SDR Blog V3 that are exposed for experimental and bespoke projects. As Lincoln explains:
Recently in my spare time I have been looking into developing an open-source project for the RTL-SDR blog dongles, more specifically an addon board system similar to RPi hats and arduino shields through the I2C pins.
So far, I've gotten a board footprint published on GitHub for the V3's pins.
The idea is to allow easy addition of modules like external clocks, sensors, controller boards, or even something like a LoRa chip all with minimal soldering and easy swap-ability. I also plan to design 3D models of cases for the SDR to allow it to look cleaner or be more portable in different senses.
Thank you to Nagy István for writing in and sharing with us his video showing how he uses a home-made backfire helix antenna and the JAERO software to receive and decode Inmarsat Aero at 1545 MHz. AERO messages are a form of satellite ACARS, typically containing short messages from aircraft, and some channels also support digital voice communications.
The backfire helix is an antenna design that consists of a helically wound wire, typically wound around a 3D-printed frame, attached to a large backplane. Recently, a similar design called a 'heliocone' has become popular for use with 1.7 GHz polar orbiting satellites.
In the video, Nagy shows two designs, one of his own and the other by Digitalelektro, and the good SNR that he's achieved with them in JAERO.
Thank yoy to Viol Tailer for submitting news about the release of his new software called "uAVD - Analog Video Decoder". uAVD is capable of demodulating the following:
AM (broadcast analog television - NTSC, PAL, SECAM)
FM (FPV drone video links)
RAW (composite output from VHS, camcorders, game consoles)
The software uses the uSDR software as a host, and it passes the IQ passband stream to the uAVD via a uSDR-TCP link. uSDR is a lightweight general purpose multimode software defined radio receiver Windows application that we have posted about on the blog in the past. Currently, it supports RTL-SDR, AirSpy, BladeRF, HackRF, FobosSDR, and LimeSDR devices.
The software supports full color and grayscale modes. With a wideband receiver, it will be possible to receive full-color video. With the reduced bandwidth available with an RTL-SDR, only grayscale will be available.
The image below shows it being used to receive video from a camcorder composite video output. A FobosSDR used in direct sampling mode is used to receive the signal.
uAVD Receiving Camcorder Composite Video via the Direct Sampling Input in FobosSDR
Below is a video from a user of the software demonstrating it in action.
Thank you to Craig Giles for writing in and sharing with us news about a club for teens that he's organizing called "Waveband Hack Club YSWS" for RTL-SDR dongles. Craig writes in his email:
Hack Club is a 501(c)(3) nonprofit that aims to teach teenagers how to code by building projects. Hack Club runs a variety of programs called YSWSs, or “You Ship, We Ships”, which are programs in which a teen works on a themed project and gets rewarded with a prize following the theme.
Waveband is a YSWS about RTL-SDR dongles, where teens make a computer program that uses an RTL-SDR dongle, and they get a V4 dongle and antenna kit in return. We are aiming to get more teens involved in SDR and give them the hardware to do so through this program.
The club has a clever interactive website that interested teens can go to to learn more. Currently, it appears that the club is running the program for a limited time from June 11 to July 11. During this time, teens can log on to the website and get a free RTL-SDR dongle if they submit a program they've written that uses an RTL-SDR in a unique way.
HydraSDR is a soon to be released software-defined radio based on the same design as the popular Airspy R2 SDR. However, compared to Airspy, HydraSDR claims to have "Enhanced PCB layout and RF front end with superior power/noise filtering, improved temperature dissipation and peak temperature management," as well as various other improvements. HydraSDR also has the distinction of being made in the USA, whereas Airspy is made in China.
Recently, Benjamin Vernoux, creator of HydraSDR and former collaborator on the Airspy R2 project, sent us a review unit of the HydraSDR. This post is a review of the HydraSDR. However, because the HydraSDR is based on the Airspy R2 and competes directly with it, the two units will be heavily compared.
The design of the HydraSDR is very similar to the Airspy R2, which is already known to be a high-performing SDR. Both are based on the LPC4370 microcontroller and its built-in ADC, and they both use similar firmware. The circuit layout, from the top and bottom views, is also almost identical. Benjamin notes that the internal layout has been improved and that several components, such as LDOs, have been upgraded to better ones with reduced noise.
One larger change is that HydraSDR uses a Rafael R828D tuner, instead of the Rafael R860T tuner that the Airspy uses. Both tuners are very similar in terms of operation and performance as they are based on the same design and technology. The R828D has two additional RF input pins; however, on the HydraSDR, they are unused but are routed to two uFL connectors on the bottom of the PCB for advanced users.
Airspy (Top) and HydraSDR (Bottom) PCB Top SideAirspy (Top) and HydraSDR (Bottom) PCB Bottom Side
Both the HydraSDR and Airspy come in a black anodized aluminum extruded enclosure. The Airspy's enclosure is more compact, but the HydraSDR enclosure is purposely oversized to accommodate up to three HydraSDR PCBs.
However, additional holes for two extra SMA ports and two extra USB-C ports have not been pre-drilled, so we assume the 3x unit may be a separate product coming out in the future. The HydraSDR also utilizes an SMA port for the optional CLK-IN port, unlike the MCX port on the Airspy.
Airspy (Left) and HydraSDR (Right) Side Profile
A major win for the HydraSDR is its use of a USB-C connector, whereas the Airspy R2 still uses a micro USB connector. (We note that it is a USB-C connector, but not USB3.0, it is still USB2.0).
The microUSB connector on the Airspy R2 is less robust and can easily disconnect if bumped, even with brand-new cables. The connection on the HydraSDR is rock solid, and no amount of reasonable bumping of the cable can disconnect it.
The HydraSDR spec sheet also mentions its suitability for phase-coherent applications, such as radar. However, although you can run all three from the same clock, from what we can see, specialized firmware, software, and external signal and/or noise source hardware would still be required for sample and phase alignment, as the system can not be naturally coherent. We're unsure whether the company will be directly supporting coherent use cases or if coherence is left as an exercise for the customer.
Software
Both Airspy and HydraSDR use the same USB VID/PID identifiers, so most software should recognize them as the same device.
We decided to see if it would run in SDR#, the official software of Airspy. Upon selecting the device as an Airspy R2 in SDR#, we were able to see it work and operate just like a genuine Airspy R2. We want to note that Youssef has mentioned that, in his view, using non-Airspy products like the HydraSDR with the Airspy source would be in violation of SDR# terms, but we will use it in this review for comparison purposes.
HydraSDR Running in SDR# as an Airspy R2 Device
This is interesting because in SDR++, the software recommended by HydraSDR, selecting Airspy R2 as the device results in the device being unable to connect. Currently, SDR++ does not support HydraSDR in its latest releases; however, support is being developed.
For now, until SDR++ officially supports HydraSDR, Benjamin has released a custom fork of SDR++ that will be available on the HydraSDR website.
HydraSDR Running in SDR++ (HydraSDR Fork)
We note a few differences between SDR++ and SDR#. SDR# restricts the visible bandwidth of Airspy devices to 8 MHz, as this hides the edges, which contain aliased signals. SDR++ does not hide the sides. SDR# also has an 'HDR' (high dynamic range) mode for Airspy devices, whereas SDR++ does not. More on HDR mode is discussed under the testing heading.
When HDR mode was turned OFF, no differences in performance between SDR# and SDR++ were noticed.
We are also aware that HydraSDR is now supported by gr-osmosdr (GNU Radio source block), SatDump (satellite decoding software), and URH (Universal Radio Hacker).
We also found that HydraSDR runs as an Airspy in SDR-Console V3. Official Airspy software, such as SpyServer and adsb_spy, also work with HydraSDR. We suspect that most software that supports the Airspy will be compatible.
Testing
No Antenna Test
In this test, we connected each SDR to a dummy load and used SDR# to look for signals. If the SDR is shielded well, no signals should be received.
We noticed that the HydraSDR has excellent shielding and is very well protected against signals entering through paths other than the antenna. The Airspy was able to receive a strong TV channel without any antenna, indicating that it has shielding issues.
HydraSDR (Left) Airspy (Right) No Antenna Connected
Across the spectrum, the HydraSDR also has a cleaner spectrum with lower power levels on most internal spurs.
Real World SNR Tests
In this test, we received real-world signals with each SDR connected to a roof-mounted Discone, which was in turn connected to a splitter. We increased the gain settings to optimize each SDR for best SNR, which is typically just before it overloads and creates images.
We noticed that the gain distribution on the HydraSDR was slightly different from that of the Airspy, as the HydraSDR would overload on a lower gain setting compared to the Airspy. When optimizing for SNR we found that a gain setting 1-3 notches higher on the Airspy was required.
Once optimized, we found that results were very similar, with a slight 0.5 - 1 dB sensitivity edge going to the HydraSDR; however, this may be within chip-to-chip variances, so we can't say for certain if one is more sensitive than the other.
HydraSDR (Left), Airspy (Right). Same SNR on BCFM in SDR#HydraSDR (Left), Airspy (Right). Same SNR on BCFM in SDR++HydraSDR (Left), Airspy (Right). Slightly better SNR for the HydraSDR at 457 MHz.
Real World Comparison SDR++ vs SDR# 1921
HydraSDR recommends using SDR++, whereas Airspy recommends using the Airspy native software SDR#. While HydraSDR currently works on SDR#, we're not sure if this will continue, as SDR# could possibly block the use of clones and spinoffs. So, it seems fair to compare HydraSDR with SDR++ and Airspy with SDR#.
Under normal operation, with moderate strength signals, both programs appear to give nearly identical performance in terms of audio quality and signal SNR.
However, Youssef has pointed out that SDR# (and SDR-Console) has a special mode called HDR (high dynamic range) available for Airspy products. HDR mode works by optimizing the DSP chain specifically for the Airspy hardware whenever decimation is used. With HDR mode on, we can push the gain setting much higher than we would have otherwise without experiencing overload, resulting in a better SNR.
We are currently aware that only SDR# and SDR-Console V3 implement the Airspy HDR mode tweaks, and SDR++ does not.
Comparing performance between two different programs can be a bit tricky because each uses a slightly different FFT algorithm, resulting in different SNR values being calculated. SDR++ consistently calculates a somewhat higher SNR for the same signal.
To illustrate the effect of the Airspy HDR mode, we will use two SDR# instances and disable HDR mode for the HydraSDR, simulating the effect of using it in SDR++, which does not have HDR mode.
HydraSDR with HDR Mode OFF (Left), Airspy (Right) HDR Mode ON
This test showed a rather dramatic +7 dB improvement with HDR mode on. With HDR mode on we were able to increase the gain much further without overload. In the screenshot we increased the gain as far as possible to optimize the SNR on each receiver as much as possible.
For an audio comparison that directly compares Airspy on SDR# vs HydraSDR on SDR++, here is an audio file of the Airspy running SDR# with HDR mode ON, 16x decimation, receiving a weak signal sandwiched between strong signals.
And here is the audio file of SDR++ with 16x decimation receiving the same signal.
Both signals were optimized for the best SNR possible which was just before the SDRs overloaded and displayed intermodulation products. There is a clear difference in audio quality that can be heard, with SDR # emerging as the winner. Note that these HDR improvements may only be seen in a high dynamic range environment (when strong signals are mixed with weak signals) and when decimation is used .
Conclusion
With the Airspy R2 starting to feel a bit dated, the HydraSDR looks to be a great addition to the choice of available SDRs. However, we consider it to be essentially a spinoff of the Airspy with some minor changes made to improve performance and usability. The improved shielding and USB-C port are particularly notable enhancements that we love. Compared against the Airspy, HydraSDR is clearly the better hardware choice.
But if you already have an Airspy R2, there are not enough improvements here to consider the HydraSDR as a next-generation upgrade worth purchasing. That said, if you're looking for a new SDR made in the USA, the HydraSDR should be on your radar.
The Airspy maintains some software advantages, such as official software support and compatibility with SDR#’s and SDR-Consoles HDR mode, which excels in strong signal environments. However, the HydraSDR is directly compatible with the Airspy and currently functions as one in SDR#, allowing it to benefit from HDR mode as well. But this compatibility relies on SDR# not actively blocking it. It's also important to note that Youssef has mentioned that, in his view, using the HyraSDR in SDR# would be in violation of the SDR# licensing agreement, as would loading the HDR enhancements in SDR-Console V3 with HydraSDR (note that we have not verified the legality of this claim).
We also note that Benjamin wants to emphasize that HydraSDR is not designed for use with SDR#, and only SDR++ and other HydraSDR software should be used with it.
Disclaimer
We have no financial interests in either Airspy or HydraSDR (apart from reselling the YouLoop). The Airspy R2 used in this review was provided to us back in 2015 as a free review unit, and HydraSDR was provided to us recently as a free review unit. Transparency note: Certain parties have claimed that we gave an unfair review to the HydraSDR because they claim that we take referral credit from sales of Airspy units. This is not true. Several years ago, when Airspy was the main recommended upgrade to the RTL-SDR, we briefly trialled a referral program with Airspy, but that program ended many years ago. Any leftover referral links from old blog posts are no longer active. The only Airspy product we sell on our store is the YouLoop antenna, which is unrelated to the SDRs themselves. Some parties have also pointed out that parts of the original review have been removed, and they claim a lack of transparency. In a previous iteration of the review, we mentioned our thoughts and speculation regarding IP law, but removed these sections due to legal threats.
Airspy has just announced the start of its yearly summer sale, offering 20% off all Airspy products from June 27 to June 30, 2025. The summer sale has historically only been 15% off, so this year there is an extra discount.
Airspy R2:US$169.00 US$135.20
Airspy Mini:US$99.00 US$79.20
Airspy HF+ Discovery:US$169.00 US$135.20
Airspy SpyVerter R2:US$49.00 US$39.20
YouLoop Antenna:US$39.95 US$31.96
The sale is active at all participating resellers, which includes our own store, where we have the YouLoop on sale for US$31.96, including free shipping to most countries worldwide (excluding tariffs!).
We also note that recently, iTead, Airspy's manufacturing partner in China has opened a US warehouse, which means that US customers ordering from their store will not experience high tariffs. iTead sells all Airspy products, except for the YouLoop.
