In the HackRF Pro specifications we’ve mentioned improved RF performance compared to HackRF One. Now that we’ve finalized any last tweaks to the RF front-end and production is well underway, we’d like to share some more details about the improvements.

One key metric for radio systems is sensitivity, which measures the minimum signal strength that a receiver can detect. However, for software defined radio hardware, sensitivity is difficult to define in a useful way as it changes depending on the modulation scheme in use and even the software implementation.

Instead we can look at noise figure: this measures the degradation in signal-to-noise ratio caused by components in the RF signal chain, so it gives a good representation of the hardware’s contribution to achievable sensitivity. The higher the noise figure of the hardware, the more noise and/or loss it contributes, so we would like the noise figure to be as low as possible.

We’ve been using noise figure measurements throughout HackRF Pro development to optimize the RF front-end and the tuning algorithm that picks LO/IF frequencies. We do this by using a switchable wide-band noise source that generates a known level of noise (HP 346B) along with SDRAngel’s noise figure measurement plugin.

Below is a comparison between HackRF One and a final prototype of HackRF Pro:

This shows typical expected values, measured from single HackRF One and HackRF Pro prototype units; there may be small changes from unit to unit and also if we make further changes to the tuning algorithm. The measurement is also quite susceptible to external interference, so the result can be affected by ambient RF signals in the lab.

The plot shows a solid improvement across almost the whole tuning range, with significant improvement at higher frequencies. In particular the extra tuning range above 6 GHz is now more useful. The plot is also much smoother, thanks to better PCB layout and signal integrity and an improved tuning algorithm.

I wanted to do some extra testing to demonstrate how this plays out in a real-world example, so I set up a head-to-head comparison between HackRF One and HackRF Pro receiving ADS-B location data from planes. I set both of them up in a window in a fairly challenging location with limited sky view and no view of the horizon, so most signals would be reflected off buildings and be pretty weak. They each used a simple dipole tuned for 1090 MHz attached directly to the HackRF, so no extra amplification or filtering.

The plot below shows maximum observed coverage after collecting data for a few hours, with HackRF One in red and HackRF Pro in blue:

In this test the HackRF Pro generally got around 15 to 50 km extra maximum range, and also received double the number of valid messages.

Then to see how well it could do in good conditions, I took the HackRF Pro up a hill with almost 360° horizon view, and received some positions out to almost 400 km!

I was really impressed to see that sort of reception range with just an antenna directly attached. These ADS-B observations have made it clear that our hard work to reduce HackRF Pro’s noise figure resulted in improved receive sensitivity in the real world, and we’re excited to see what interesting applications people have for it.

Great Scott Gadgets is committed to supporting the open source community. One way we give back to the community is by giving away Free Stuff! If you or your community organization would like Free Stuff from Great Scott Gadgets, please fill out our Free Stuff Application to the best of your ability.

Our team judges applications based on community impact and clarity of project description, so please be detailed. Please know that this program is focused on supporting communities and requires your project be open source. We send hardware out to people looking to spread education, support community projects, or contribute to open source projects or research. We are not interested in sending hardware out to companies or to individuals for strictly personal use at this time.

Still have questions or need some advice? Here’s a basic walkthrough of the application!

Demographics

These questions help us get to know about you or your community organization and the projects you do. Information from this portion of the application is also essential for posts for the Great Scott Gadgets Free Stuff blog posts - we want to make sure all of our information is correct!

Please tell us your:

Full name (and group name if you are applying as a group or organization!)

Email address (so you may be contacted if your application is selected)

Country

Pronouns (she/her, he/him, they/them, etc.) - Please note that failure to answer this question in a respectful manner is grounds for automatic disqualification! If you need help with this question, feel free to ask. Note: if applying for multiple people, it is okay to put they/them to refer to the collective group, or the pronouns of each individual member applying.

Social media accounts where you share your project work, if applicable

Project Details

These questions help us determine the eligibility of your project for our Free Stuff Program. Applications that are accepted are usually as detailed as possible and give us a good idea of how one of our products will be incorporated into a project.

Please tell us:

• What Free Stuff would you like to receive? Please note that we typically only send out one device to a recipient, unless otherwise appropriate.

Please describe the project you will be using the requested device for. Please note that applications that are accepted are usually 200+ words, so please be as descriptive as you can! A good start to an application can look like…

• ”We are a student-run hardware design lab at a university looking to give students access to tools they may not typically be able to afford or find in maker spaces. We offer workshops and have a planned curriculum planned to incorporate a HackRF One into a series of lessons on software-defined radio, wireless security testing, and digital signal analysis.”

• ”I am a university student seeking a HackRF One to implement into my thesis project where I will be building a digital radio receiver for decoding NOAA weather signals with open source software.”

• ”I’m an educational content creator looking to create a series of videos covering advanced RF projects that users at home can follow along with, backed up by open source documentation.”

While applications that typically get rejected look like…

• ”It’s my birthday and I want a Cynthion”

• ”I think it would be cool to have a HackRF One”

• ”I want to learn about SDR”

• What work have you already completed on your project? (Please include a link to an open source repository if you’ve got one).

• Why is the device you requested the right one for the project you are working on?

• What open source licensing are you using on your project? Examples of this can include MIT License, GNU Licenses, and Apache License, and more. Reminder that we typically require candidates’ projects to be open source.

Please do not submit any content that has been created or altered by a large language model or similar technology, including but not limited to ChatGPT, CoPilot, and Gemini.

Please note that Free Stuff Program applications remain valid through each calendar year. If you are not selected by the end of the year, your application will be considered void, but we encourage you to apply again when the next round of applications opens! If you have any questions about the application process, the status of your application, or the Free Stuff Program in general, you can email freestuff@greatscottgadgets for assistance.

We advertise 100 kHz as the lower edge of HackRF Pro’s operating frequency range, but that isn’t a hard limit. While working on the design, I realized that it should work fairly well to pick up longwave time signals such as WWVB, broadcast at 60 kHz from Colorado, USA.

WWVB provides a stable frequency reference and time code. If you have a radio-controlled clock in North America, it probably uses the signal from WWVB to maintain the correct time. WWVB can also be used to discipline a laboratory frequency standard, eliminating the need for a local atomic clock in many cases.

Why use WWVB?

Nearly every electronic device contains some sort of oscillator or clock. HackRF Pro, for example, contains a temperature-compensated crystal oscillator (TCXO) which is better than the crystal oscillator (XO) used in HackRF One. Having a better internal clock means that radio frequencies received or transmitted by the device are more accurate. If I receive a radio signal at 1 GHz with HackRF One, I can’t be sure if the signal over the air is at exactly 1 GHz. The received frequency as detected by HackRF One might be 10 or 20 kHz off. With HackRF Pro the frequency uncertainty is an order of magnitude smaller, thanks to the built-in TCXO. I would be confident that any inaccuracy at 1 GHz is no more than about 1 or 2 kHz, even without performing any calibration.

I need to use an even better clock in my lab to be certain that the oscillators in our products perform as expected. I could use a HackRF Pro to measure the frequency error of a HackRF One, but how do I know I can trust the HackRF Pro? I would need a more trustworthy frequency reference such as an atomic clock. A good alternative to an expensive atomic clock would be an oven-controlled crystal oscillator (OCXO) that has been recently calibrated or that is disciplined by a remote atomic clock.

One such remote frequency reference is WWVB which has several orders of magnitude less frequency uncertainty than the TCXO in HackRF Pro. WWVB also provides a digital time code indicating the time of day.

Why not a GPSDO?

Folks like me who need a lab frequency standard typically turn to a GPS disciplined oscillator (GPSDO). I could purchase an off-the-shelf GPSDO that disciplines an internal OCXO with a signal received from GPS (or other GNSS) satellites. Such a device would cost a few hundred dollars, much less than the thousands of dollars required to buy a small atomic clock.

Before GPSDOs became available, some test equipment manufacturers sold WWVB disciplined oscillators, but these products are no longer made. They had already become unpopular before the broadcast format of WWVB was changed in 2012 with the introduction of phase modulation that broke compatibility with commercial oscillators. There is no reason that a new WWVB disciplined oscillator could not be made. In fact, many hobbyists have made their own or have modified older oscillators to make them compatible with the new phase modulation.

I like the idea of having my own WWVB disciplined oscillator, partly because a GPS receiver needs an active antenna placed somewhere with a view of the sky whereas a WWVB receiver can be located indoors. I like that a WWVB receiver can have a relatively simple design and does not need to constantly track multiple moving satellites. I like that WWVB is stable and will not be adversely affected by Kessler syndrome.

I like that a WWVB receiver implementation with HackRF Pro can be used to directly measure the frequency error of the HackRF Pro itself by simply measuring how far off from 60 kHz WWVB appears to be. I don’t even need to build a whole WWVB disciplined oscillator to do this. (In theory I could do the same thing with GPS, but it would require significantly more complex software.)

Most of all, I think that receiving WWVB is a fun project!

An active antenna for 60 kHz

Radio antennas are generally sized in proportion to wavelength, and the wavelength at 60 kHz is very long, about 5000 m. A vertically polarized quarter-wave monopole antenna for 60 kHz would be the tallest structure in the world! To avoid such an impractical construction, the WWVB transmit antenna has a more complex design. Although small compared to the wavelength, the broadcast antenna is comprised of hundreds of meters of cable and multiple towers.

WWVB receivers use small loop antennas which detect changes in the magnetic field. Several amateur radio operators have constructed air core loop antennas for WWVB with diameters of one to two meters while radio-controlled clocks use much smaller ferrite core (“loopstick”) antennas. I thought it would be fun to build a small active loopstick antenna that is compatible with HackRF Pro.

For my initial experiment, I pieced together a few RF amplifier and filter test PCBs and connected them to a loopstick antenna pulled from an AM radio kit. I used a VNA to tune the antenna for 60 kHz with a parallel capacitor. With two amplifier ICs (which I had previously tested for the URTI project) and a low-pass filter, I was barely able to detect a faint signal at 60 kHz one afternoon using a HackRF Pro. Later that evening the signal was stronger and easily identifiable as WWVB. I live in Ontario, Canada, over a thousand miles away from WWVB, and I think it’s pretty nifty that I could pick up the signal from such a long distance on my first attempt!

Based on this success, I designed Teewee, an active loopstick antenna named for (the popular name of) the similarly shaped Tetris block. Teewee consists of a small PCB that performs amplification and filtering, a hand-wound ferrite core, and a 3D-printed enclosure. While my initial experiment required an external power supply, Teewee is powered by HackRF Pro’s built-in bias tee.

Inspired by an older design, I used an instrumentation amplifier for Teewee’s first stage. The purpose of this is to isolate the magnetic field (which is seen by the amplifier as a differential signal) from the electric field (which is seen as a common-mode signal). Instrumentation amplifiers have high common-mode rejection, eliminating much of the electric field noise that likely originates locally.

My first test with Teewee was disappointing. I detected WWVB not at all, instead picking up pulses of broadband noise. After a frustrating couple of days, I decided to reproduce my original setup and found that it had the same poor result! The reason was that I had recently rearranged my lab and had placed my PC tower on my desktop, close to the antenna test area. While Teewee is designed to reject electric field interference, it is highly sensitive to magnetic interference, something my PC evidently produces quite a bit of. Fortunately, I was able to eliminate this near-field interference by moving the antenna just half a meter farther away from the PC.

After solving the near-field problem, I found that Teewee actually performed quite well. While my original setup was useful only during periods of favorable ionospheric propagation at night, I was able to pick up WWVB at any time of day with Teewee.

Observing the WWVB signal

A distinguishing characteristic of WWVB is that the very precise carrier frequency of 60 kHz turns off and back on once per second with varying pulse duration. With most receivers it looks like on-off keying (OOK), but it is actually amplitude-shift keying (ASK) where the “off” periods are 17 dB lower power than the “on” periods. At times when propagation is good, I can barely detect the signal during the “off” periods with Teewee.

Pulse width modulation (PWM) carries time of day and other status information in 60-second data frames. The falling edge of each pulse occurs at the start of each second. Once every ten seconds there is an extra-long “off” period. This pattern makes it easy to identify the signal when there is sufficient signal-to-noise ratio to observe the modulation.

Since 2012 the phase of each pulse carries a second data stream. The last time I experimented with WWVB was prior to 2012, so I hadn’t observed the phase modulation before. The phase modulation is binary phase-shift keying (BPSK) at one bit per second with the phase transition happening 0.1 seconds into the “off” period. Using a derived phase plot in inspectrum I was able to see the phase abruptly change from one pulse to the next.

In theory, the BPSK modulation makes it possible to implement a receiver capable of detecting a weaker signal than can be achieved with an ASK receiver, particularly once per hour when the BPSK stream carries an extended symbol sequence that lasts 6 minutes and includes a fixed 106-bit synchronization word. I think it would be interesting to try detecting this “medium mode” from farther away, maybe even on another continent.

When using WWVB as a frequency reference, the digital modulation can be ignored except that the detector (software, in my case) must be designed to tolerate BPSK.

Measuring Doppler shift with WWVB

Shortly after getting Teewee working, I traveled to British Columbia, so I decided to try picking up WWVB on my flight across Canada, hoping that I would be able to see the Doppler shift from the motion of the aircraft relative to the transmitter. I found that I was unable to detect the signal with the antenna at my seat in the aircraft but that I could pick it up by placing Teewee in a window, connected to a HackRF Pro by an SMA cable. I captured the signal from WWVB for a full hour while the aircraft headed west, starting from a point roughly north of the transmitter.

I analyzed the hour-long capture and found that the Doppler shift was, in fact, evident when plotting the received WWVB frequency over time. About halfway through the capture, the aircraft changed course, and this caused an abrupt change of frequency that clearly confirmed that I really was seeing the Doppler effect.

As further confirmation, I later downloaded ADSB flight data and used it to plot the expected Doppler shift. This correlated quite well with the WWVB observations. Apart from some blips due to interference, the primary discrepancy between the expected and observed Doppler shift was an offset of 15 mHz due to the HackRF Pro TCXO being 250 ppb slow. (This TCXO was better than average. I typically see frequency error of approximately 1 ppm.)

I had hoped to acquire an even longer capture on the return flight to Ontario, but there was too much interference, perhaps from avionics or from a jet engine. This was on a smaller aircraft, and I was seated at the front edge of the wing, adjacent to an engine.

Try it yourself

I’ve published the Teewee design for anyone who would like to build their own. Teewee is intended for use with HackRF Pro, but I’ve also had some limited success with HackRF One even though it has significantly worse 60 kHz performance than HackRF Pro.

Since our previous timeline update, we have encountered additional unexpected delays in our production progress. These delays are the result of a necessary hardware revision to account for MacOS users. During late stage testing, our team encountered issues with USB signaling on Mac devices, and while able to find potential workarounds, agreed that the next step would be to modify the PCB design to address this issue. HackRF Pro will ship as r1.2.1, our final revision. We decided that this revision was imperative to ensure that all users could have an equal user experience with HackRF Pro, regardless of operating system.

As a result, our new projected shipping window is December 2025.

We appreciate the patience and support we have received during this exciting transition period for Great Scott Gadgets. While another board revision was not in our original plans, we are confident in our decision to prioritize quality and user experience over meeting our original deadline.

Learn More:

Visit the HackRF Pro product page for full specs and reseller pre-order links. The open source design, migration guide, and user documentation will be published prior to initial shipment. We invite you to join the discussion in the #hackrf channel on our Discord server!

The belated June 2025 recipient for the Great Scott Gadgets Free Stuff Program is Ashen Chathuranga, a university student from Sri Lanka. He is working on a project involving the development of an open source satellite monitoring station and requested a HackRF One to conduct his research. He will also be researching radio wave penetrating materials for his university. Being able to assist students in need of equipment for academic research and goals is one of our primary goals for our Free Stuff Program, so we are happy we were able to help Ashen out!

The belated July 2025 recipient for the Great Scott Gadgets Free Stuff Program is Murat Sever, a professor from Turkey who teaches at TOBB ETU University and recently ran a workshop titled “Simple Replay Attack Demo with GNU Radio.” In this workshop, Murat utilized several open-source software and hardware tools to demonstrate how to receive and transmit RF signals. Workshop participants then used SDR and GNU Radio to perform replay attacks with the captured radio signals. We sent a handful of HackRF Ones to Murat for participants to learn and experiment with in this workshop. He has also informed us that the HackRF Ones will be put to use in the course he is teaching this fall on SDR applications! We are glad that we could continue to support Murat’s efforts to educate others about the capabilities of software defined radio and wish him and his students best of luck with their fall term!

The belated June 2025 recipient for the Great Scott Gadgets Free Stuff Program is Joe Caton from the United States! Joe has requested a HackRF One for his senior project. He has the opportunity to work with a local wildlife preserve and assist them in an ongoing project to track and study the behavior of the large population of eastern box turtles nearby. Joe will be aiding the nature center in developing quality, low cost alternatives to their current tracking technology. He plans to refine their current VFH tracking modules and implement HackRF One into a more compact system that will enable image recognition capability in the field to identify specific turtles. He hopes that this could lead to similar systems being replicated for other wildlife preserves and contribute to an open source repository so foundations with less funding can have access to accurate and successful DIY monitoring systems. We are looking forward to hearing about the progress and outcome of Joe’s project and excited to assist in this unique application of our hardware!

The belated May 2025 recipient for the Great Scott Gadgets Free Stuff Program is Nagamani C Gunjal, a university student who has requested a HackRF One for an academic project that involves research and demonstration of real-world vulnerabilities in consumer and commercial drones by analyzing and manipulating radio communication protocols. Her focus is on ethical hacking and the security testing of drones that operate using RF signals, specifically targeting control signals transmitted between the radio transmitter and onboard radio receiver module of the drone. This project is part of a broader study on UAV (Unmanned Aerial Vehicle) security with an ultimate goal of proposing and implementing improved countermeasures for secure UAV communication. She has told us that the requested device will be essential for capturing, decoding, and replaying drone communication signals in controlled environments for testing purposes!

The belated April 2025 recipient for the Great Scott Gadgets Free Stuff Program is Ashen Chathuranga from Sri Lanka! Ashen is a university student who plans to use the HackRF One we are sending him for multiple academic projects, including an open source satellite monitoring station and researching radio wave penetration. We are glad we could provide Ashen with equipment to further his education and support his academic journey!

The belated March 2025 recipient for the Great Scott Gadgets Free Stuff Program is Mrinal Kumar from India! Mrinal is currently running a small, free cybersecurity learning group for young adults aged 18-21 who come from financially limited backgrounds. Currently, there are about 15 students who actively participate in regular meetings to study the fundamentals of cybersecurity, ethical hacking, and responsible digital security practices.

We will be sending Mrinal and his students a HackRF One so he can introduce them to software-based cybersecurity and the world of wireless and RF security. He tells us that they will explore signals, learn about vulnerabilities in everyday wireless systems, and will safely demonstrate examples of real world attack and defense scenarios. His vision of providing accessible, hands-on learning for students who would not otherwise have an opportunity to dive into the world of open source hardware and software defined radio aligns pretty perfectly with ours! We are excited to see what Mrinal and his students accomplish and discover with their new equipment.