Tired of static on your AM or shortwave radio? Do you struggle to hear distant stations? There is a simple fix. You can build a special antenna that makes radio signals much stronger. This guide shows you how to build a DIY active antenna. It is a fun project that can give you crystal-clear reception.
https://vu3dxr.in/simple-diy-active-antenna-for-crystal-clear-reception/
July 15, 2025 - The software-defined radio (SDR) community has a new contender as the HydraSDR RFOne emerges as a direct competitor to the popular Airspy R2, with detailed technical analysis from electronics expert VU3DXR highlighting both its potential and market implications.
The Software Defined Radio (SDR) landscape has recently been joined by the HydraSDR RFOne, a new receiver sparking interest in amateur radio and SDR enthusiasts. The HydraSDR RFOne is a USB software-defined radio receiver designed for professionals, researchers, and radio enthusiasts as a direct competitor to Airspy R2.
The device features impressive specifications including 10MHz instantaneous bandwidth sampling capability across 24MHz to 1800MHz, with expandable features and frequency coverage through extension modules. Built with a high-grade 7075 aerospace aluminum enclosure, the receiver targets professionals, researchers, and radio enthusiasts seeking advanced SDR capabilities.
The technical blog VU3DXR has provided comprehensive coverage of the HydraSDR RFOne through two detailed articles:
Created by Benjamin Vernoux, who also contributed to the original Airspy design, the HydraSDR RFOne represents both continuity and evolution in SDR technology. The device's deliberate positioning as an Airspy R2 competitor has generated significant discussion within the SDR community.
Key improvements over its predecessor include enhanced PCB layout, superior RF front end with better power and noise filtering, improved temperature dissipation, and more robust USB-C connectivity. The device also features an extensible design with open firmware, appealing to developers and researchers requiring customization capabilities.
The HydraSDR RFOne is now available through major electronic component distributors including DigiKey, marking its transition from development to commercial availability. The open-source nature of its firmware has been particularly well-received by the developer community.
Multiple references to the HydraSDR RFOne have appeared across various VU3DXR blog posts, indicating sustained interest from the technical community. The device has been consistently featured alongside other significant SDR developments on the VU3DXR electronics blog.
As the SDR market continues to evolve, the HydraSDR RFOne's introduction represents a significant development for professionals and enthusiasts seeking alternatives to established platforms. The detailed technical coverage from VU3DXR provides valuable insights for potential users evaluating this new hardware option.
The device's success will likely depend on its ability to deliver on its promised improvements while maintaining competitive pricing in an increasingly crowded SDR market.
For complete technical specifications and detailed analysis, visit the VU3DXR blog at vu3dxr.in for comprehensive coverage of the HydraSDR RFOne and other SDR developments.
A terminated antenna is a specialized antenna design that incorporates a resistive load or termination at one end to prevent signal reflections and improve performance characteristics. Unlike conventional antennas that rely on resonance, terminated antennas use controlled absorption to achieve broadband operation and consistent impedance matching across wide frequency ranges.
For more detailed technical analysis and practical implementations, read our comprehensive articles on terminated end-fed antennas at vu3dxr.in.
Terminated antennas offer several distinct advantages over traditional antenna designs. The primary benefit is their exceptional bandwidth capability, often spanning multiple octaves without significant performance degradation. This makes them ideal for applications requiring operation across diverse frequency bands.
The termination element, typically a resistor matched to the antenna's characteristic impedance, eliminates standing waves that commonly plague unterminated designs. This results in improved VSWR (Voltage Standing Wave Ratio) performance and more predictable radiation patterns.
Terminated antennas are extensively used in military communications, electronic warfare, and radar systems where broadband operation is critical. Their ability to maintain consistent performance across wide frequency ranges makes them valuable for frequency-hopping communications and broadband jamming applications.
RF test equipment manufacturers frequently incorporate terminated antennas in their designs to ensure accurate measurements across broad frequency spectrums. These antennas provide stable reference points for antenna analyzers, spectrum analyzers, and other measurement instruments.
In broadcasting applications, terminated antennas serve as backup systems or for specific coverage requirements where broadband performance outweighs efficiency considerations.
When selecting a terminated antenna, several factors must be evaluated. Power handling capability is crucial, as the termination resistor dissipates significant RF energy as heat. Proper thermal management ensures reliable operation and prevents component failure.
The termination impedance must be carefully matched to the antenna's characteristic impedance to achieve optimal performance. Most terminated antennas use 50-ohm terminations to match standard RF system impedances.
For detailed design guidelines and practical construction tips, check out our terminated end-fed antenna guides at vu3dxr.in.
Advantages:
Limitations:
Proper installation of terminated antennas requires attention to mechanical support and thermal considerations. The termination resistor generates heat during operation, necessitating adequate ventilation or heat sinking in high-power applications.
Regular inspection of termination components is essential for maintaining optimal performance. Resistor degradation due to thermal stress can affect antenna characteristics and should be monitored.
Advanced terminated antenna designs are incorporating active termination circuits and smart materials to enhance performance and reduce limitations. These innovations promise improved efficiency while maintaining the broadband advantages that make terminated antennas valuable in modern RF systems.
Terminated antennas represent a crucial technology for applications requiring broadband operation and consistent performance across wide frequency ranges. While they sacrifice some efficiency compared to resonant designs, their unique characteristics make them indispensable for many specialized applications in communications, testing, and defense systems.
Understanding the principles and applications of terminated antennas enables engineers to make informed decisions when selecting antenna solutions for challenging RF requirements.
For more in-depth technical analysis and measurement data on terminated end-fed antennas, visit our detailed articles at vu3dxr.in. Our blog regularly features comprehensive antenna studies, measurement methodologies, and real-world implementation examples that can help advance your RF engineering projects.
The world of compact shortwave radio receivers has been revolutionized by the introduction of Silicon Labs' SI4732 chip, which powers two popular budget-friendly options: the ATS Mini and ATS20+. These portable DSP (Digital Signal Processing) receivers have gained significant traction among radio enthusiasts, amateur radio operators, and shortwave listening (SWL) communities worldwide. This comprehensive guide examines both devices, their technical specifications, performance characteristics, and real-world applications.
Both the ATS Mini and ATS20+ are built around the Silicon Labs SI4732 chip, which serves as the core of their radio reception capabilities. The comprehensive SI4732 technical analysis on VU3DXR.in details how the SI4732 provides comprehensive frequency coverage including AM/MW (520 kHz to 1710 kHz), LW (153 kHz to 279 kHz), SW (2.3 MHz to 26.1 MHz), and FM (64 MHz to 108 MHz) with RDS support.
The chip's advanced DSP features include automatic gain control (AGC), bandwidth filtering with selectable options, beat frequency oscillator (BFO) for SSB demodulation, and signal strength indication (RSSI). However, as noted in critical reviews, "the Si4732 chip brings inherent limitations that no amount of clever implementation can fully overcome."
The ATS Mini represents a sophisticated approach to portable radio design, leveraging the powerful ESP32-S3 microcontroller platform. According to technical documentation, the device features the Espressif ESP32-S3-WROOM-1-N16R8 module, which provides:
The device incorporates a 1.9-inch ST7789 IPS display with 170 × 320 pixel resolution, providing comprehensive user interface functionality including frequency readout, operating mode display, signal strength meter, and battery status indicator.
The ATS Mini's audio subsystem consists of digital audio processing through the SI4732 chip, with the ESP32-S3 handling additional audio processing and volume control. The system includes a built-in 1511 series speaker (8 ohms, 1W) and 3.5mm headphone jack for private listening.
User reviews from the Spanish trip documentation indicate that "the speaker may sound a touch better, but good headphones made a big difference," suggesting that while the built-in speaker is adequate, the device performs optimally with quality headphones.
The ATS Mini utilizes a lithium-ion 603040 battery with 800 mAh capacity, providing approximately 10+ hours of continuous operation. However, recent technical reviews have identified significant power management issues, particularly with newer firmware versions.
Critical analysis from VU3DXR.in's detailed power management review reveals that "recent ATS Mini variants suffer from a critical battery discharge problem that renders the receiver nearly unusable," with excessive standby current draw often exceeding 50mA even when the unit appears to be "off." This has resulted in fully charged batteries draining completely within 24-48 hours of non-use.
The ATS Mini runs on open-source firmware developed by the radio enthusiast community, based on Ralph Xavier's ESP32 OLED_ALL_IN_ONE sketch. The device supports multiple programming and customization options through Arduino IDE and PlatformIO compatibility.
Recent firmware updates have introduced innovative features such as EiBi integration, which provides station information cycling at the bottom of the screen during frequency tuning. As noted in VU3DXR.in's firmware update coverage, "The EiBi integration is a wonderful addition! I've been enjoying it for the last few days."
For users looking to customize their ATS Mini experience, VU3DXR.in provides comprehensive firmware flashing guides that detail the process for updating and customizing the device.
The ATS20+ represents an upgraded version of the ATS-20, featuring a 0.96-inch OLED display and pre-configured commercial and ham radio bands. Unlike the ATS Mini's experimental approach, the ATS20+ is marketed as a full-band receiver with comprehensive DSP and SDR capabilities.
Key features include:
Technical comparisons reveal that the ATS20+ demonstrates superior sensitivity across AM, FM, and SW bands. Users report successful reception of major broadcasters like China Radio International and Voice of Greece, as well as utility stations like HF VOLMET. The device performs particularly well with external antennas, such as 16-foot wire configurations.
However, the ATS20+ can overload easily with strong signals, requiring AGC adjustments or shorter antennas to mitigate interference. FM reception is notably strong, with fast RDS display capabilities.
The ATS20+ offers decent SSB reception with independent LSB/USB modes and variable BFO control. Firmware updates, particularly those from community developers, enhance SSB accuracy by allowing BFO calibration to correct frequency offsets.
Despite these improvements, SSB audio can suffer from overload and AGC clipping with strong signals, and the BFO offset exhibits non-linear characteristics (450 Hz at low HF to 1.9 kHz at high HF).
The build quality comparison reveals significant differences between the two platforms. According to VU3DXR.in's detailed build quality analysis, the ATS Mini suffers from quality control issues, with multiple vendors producing different versions without standardization. Units often ship with improperly soldered components and inconsistent build quality.
In contrast, the ATS20+ features an aluminum alloy case that provides better durability and heat dissipation, though the design can trap heat during extended use. The button layout is more refined, though still somewhat cramped.
Technical testing, as documented in VU3DXR.in's comprehensive sensitivity comparison, indicates that "the ATS20+ edges out the ATS Mini in sensitivity, offering better performance for SW and MW reception, especially with external antennas." The ATS Mini's performance varies significantly between versions, with the V3 showing improvements over earlier variants but still falling short for weak signal detection.
For detailed performance metrics and real-world testing scenarios, VU3DXR.in provides extensive coverage of both devices under various operating conditions.
The SSB performance comparison strongly favors the ATS20+. While the ATS Mini struggles with SSB clarity due to limited BFO control and coarse tuning steps, the ATS20+ provides better audio clarity, tunable BFO, and firmware upgrade potential.
VU3DXR.in's detailed SSB analysis provides comprehensive testing results showing that "the ATS20+ significantly outperforms the ATS Mini in SSB reception, offering better audio clarity, tunable BFO, and firmware upgrade potential. The ATS Mini is not a viable option for serious SSB listening."
Both devices occupy the bottom tier of the market, with the ATS20+ priced around $33-41 and the ATS Mini typically $20-30. According to VU3DXR.in's market analysis, "the rock-bottom pricing reflects severely compromised performance, poor build quality, and limited longevity." This pricing strategy allows entry-level access to DSP radio technology but comes with significant trade-offs in performance and reliability.
The ATS Mini benefits from an active open-source development community. The official firmware releases are available through GitHub repositories, with both OSPI and QSPI variants depending on the specific ESP32-S3 PSRAM type. Firmware flashing guides detail the process for updating and customizing the device.
Alternative firmware options include contributions from developers like G8PTN and community-driven projects that build upon Ricardo Caratti's (PU2CLR) comprehensive Arduino library for the SI47XX family.
The ATS20+ also benefits from community-driven firmware development, with updates that improve ergonomics, SSB calibration, and band coverage. The comprehensive firmware flashing guide on VU3DXR.in involves transferring new firmware files to the microcontroller's memory, typically requiring a Micro USB connection and appropriate flashing tools.
Additional firmware resources and troubleshooting guides are available through VU3DXR.in's ATS20+ section, providing users with step-by-step instructions for firmware updates and customization.
Both devices serve the amateur radio community, though with different strengths. The ATS20+ proves more suitable for SSB monitoring and amateur band reception, while the ATS Mini appeals to experimenters and developers interested in custom firmware development.
For dedicated shortwave listening, both devices provide basic functionality but with significant limitations compared to higher-end receivers. The ATS20+ offers better overall performance for casual SWL activities, while the ATS Mini's customization potential appeals to technically-minded users.
Both devices can serve emergency preparedness roles, though their limited battery life and build quality concerns may affect reliability in critical situations. The ATS Mini's power management issues make it particularly unsuitable for emergency use without frequent charging.
Both devices inherit the fundamental limitations of the SI4732 chip, including built-in noise and limited dynamic range. VU3DXR.in's technical analysis reveals that "the chip's built-in noise and limited dynamic range affect both models equally, setting a performance ceiling that traditional analog receivers often exceed."
Neither device excels in AGC performance, with both exhibiting overly aggressive AGC behavior that can raise background noise during SSB reception. The ATS20+ provides more control options and benefits from firmware improvements, giving it a slight advantage over the ATS Mini's basic AGC implementation.
The ATS Mini faces particular challenges from vendor proliferation, with multiple manufacturers producing units labeled as "ATS Mini" but featuring different PCB layouts, component quality, and firmware versions. VU3DXR.in's vendor analysis highlights how "this vendor proliferation makes it nearly impossible to know what you're actually buying, with no standardization or quality assurance between sellers."
Both devices benefit from active open-source development communities that continue to improve firmware, add features, and address technical limitations. The collaborative nature of development ensures ongoing improvements and customization options.
The ATS Mini platform shows potential for hardware evolution, with different versions (V1, V3) demonstrating improvements in antenna impedance adjustments and audio amplification. However, the lack of standardization between vendors complicates upgrade paths.
The ATS Mini and ATS20+ represent different approaches to budget shortwave reception, each with distinct advantages and limitations. Based on VU3DXR.in's comprehensive testing and analysis, the ATS20+ provides more consistent performance and better build quality, making it suitable for users seeking reliable basic shortwave reception. The ATS Mini appeals to experimenters and developers interested in customization potential, though recent power management issues and vendor proliferation problems significantly impact its practicality.
For users prioritizing reliability and ease of use, the ATS20+ emerges as the better choice despite its limitations. Those interested in experimental platforms and custom firmware development may find the ATS Mini appealing, but should be prepared for potential compatibility and power management challenges.
Both devices serve as entry points into digital shortwave reception rather than replacements for higher-quality receivers. They demonstrate the potential and limitations of modern silicon radio technology when implemented at budget price points, serving as functional tools for basic radio reception while highlighting the continued value of well-designed analog circuits for serious radio applications.
For detailed technical specifications, firmware updates, and community discussions, readers can explore the comprehensive coverage at VU3DXR.in, which provides in-depth analysis and user experiences with both platforms. The site features extensive ATS Mini coverage, ATS20+ reviews, and comparative analysis to help users make informed decisions.
The ongoing development of these platforms ensures that both devices will continue to evolve, potentially addressing current limitations while maintaining their accessibility to the broader radio community. For the latest updates, firmware releases, and technical insights, VU3DXR.in remains the definitive resource for ATS Mini and ATS20+ information.
This is the first time that a revolutionary device for which we are organising a joint crowd-funding campaign with Lime Microsystems is made public. The #SoDeRa is the cheapest software defined radio you can buy. The #SoDeRa will have an app store and will be able to provide any type of (bi-directional) radio communication going from LTE, Lora, WiFi, GPS, Bluetooth, radar, radio-controlled toys/robots/drone, digital radio, digital TV to even MRI scanners, satellite and air traffic communications by just installing an app. The #SoDeRa is the Arduino of the Telecom and Radio Engineer.
The SoDeRa is powerful enough to be a full MiMo LTE base station with long range coverage, provided you add the right antenna. You can via apps put other wireless communication protocols like LoRaWAN, Bluetooth, Zigbee, Z-Wave, GPS, Galileo, Airspace protocols, radar, MRI scanning RF, TV/Radio, any toy/robot/drone control, White Space, etc. But most importantly because of its price and ease of adding more protocols, the SoDeRa will enable anybody to define competing wireless communication protocols and put them into Github. Developers don’t like closed standards like LTE or complex standards like Bluetooth & Zigbee. The future will allow developers to compete against corporations and standardization bodies if they think current standards can be improved upon. The Internet has shown that this dynamic brought us easier standards through adoption like JSON and Yaml vs XML and EDI. Wireless, RF and telecom engineers never had an Arduino like the electronics engineers. The SoDeRa will plug this hole.
Including #SoDeRa in any type of smart device will greatly reduce the cost of deploying a mobile base station network because by open sourcing the hardware design it will become commodity. By including software defined radio in lots of devices, often with a completely different purpose, will allow these devices to become a smart cell via installing an extra app. In the future, support for software defined radio will likely be embedded directly in Intel and ARM chips. The foundational steps are already happening. This will likely reshape the telecom industry. Not only from a cost perspective but also from a perspective of who runs the network. Telecom operators that don’t deliver value will see their monopoly positions being put in danger. As soon as spectrum can be licensed on a per hour basis, just like any other resource in the cloud, any type of ad-hoc network can be setup. The question is not if but when. Open sourcing and crowdfunding will make that “when” be sooner than later. Smart operators that align with the innovators will win because they will get the app revenue, enormous cost reductions, sell surplus spectrum by the hour and lots of innovation. Other operators that don’t move or try to stop it will be disrupted. What do you want to be?
I am willing to pay for 1 unit
- $50 – $99 (lead time 9 months)
- $100 – $199 (lead time 6 months)
- $200 – $299 (lead time 3 months)
- $300 – $399 (lead time 2 months)
- $400 – $500 (lead time 1 month)
