The ATS Mini series represents one of the most innovative developments in pocket-sized DSP receivers for shortwave enthusiasts and ham radio operators. Built around the Silicon Labs SI4732 DSP chip and ESP32 microcontroller, these tiny radios pack remarkable functionality into an incredibly compact form factor. Let’s explore the technical evolution across all versions, from the original V1 to the latest V4. Built around the Si4732 chip and powered by an ESP32, each iteration has addressed hardware bottlenecks, from audio quality to RF interference.
ATS Mini Core Architecture: The Foundation
Before diving into version-specific differences, it’s essential to understand the shared DNA across all ATS Mini variants:
- DSP Chip: Silicon Labs SI4732 – provides excellent signal processing and reception
- Microcontroller: ESP32-S3 (varies by version) – handles user interface, control logic, and additional features
- Display: 1.9-inch IPS color screen with adjustable brightness
- Battery: 800mAh rechargeable lithium battery (USB-C charging)
- Frequency Coverage:
- LW/MW: 150kHz – 1710kHz
- SW: 1711kHz – 30MHz
- FM: 64-108MHz
- Modes: AM, FM, LSB, USB (SSB), with later firmware supporting CW and RTTY decoding
- Form Factor: Approximately 76mm × 36mm × 20mm (3″ × 1.4″ × 0.8″)
ATS MiniVersion 1 (V1): The Pioneer
The original ATS Mini V1 established the fundamental architecture that would define the entire product line.
Hardware:
- Basic SI4732 + ESP32 implementation
- Standard 50-ohm antenna input impedance
- Integrated speaker and basic audio output jack
- Plastic ABS casing
- Single rotary encoder with push-button for navigation
Performance:
- Sensitivity comparable to established portable receivers like the Tecsun PL-330
- Clean reception with the SI4732’s excellent DSP capabilities
- Limited headphone volume output due to lack of dedicated amplifier
Limitations:
- Low headphone volume – a common complaint among users
- No impedance matching for high-Z antennas
- Basic audio circuit design
- Battery drain issues in some units
Firmware:The V1 ran early firmware versions based on the open-source SI4732 libraries developed by PU2CLR (Ricardo Caratti) and other contributors. Basic functionality included manual tuning, station memory, and AGC control.
ATS MiniVersion 2 (V2): The Transitional Model
V2 was a relatively minor revision that addressed some manufacturing and design issues while maintaining the core V1 architecture.
Notable Changes
- Refined PCB layout for improved manufacturability
- Some exterior design modifications
- Firmware optimizations for better seek sensitivity
- Introduction of the AMNVOLT branding on genuine units
Production Note: V2 had a shorter production run, and AMNVOLT officially discontinued it relatively quickly. Some V2 units retained V1 exterior designs, making visual identification challenging. The manufacturer now recommends verifying version through the AMNVOLT branding and internal hardware inspection.
ATS MiniVersion 3 (V3): The Game Changer
V3 represented the first major hardware overhaul and addressed the most significant user complaints from V1/V2.
Major Hardware Improvements
1. Hi-Z Circuit IntegrationThe most significant upgrade was the addition of high-impedance antenna input circuitry. This modification involved:
- Integration of a JFET-based impedance matching circuit
- Support for wire antennas and other high-impedance sources
- Dramatically improved sensitivity with long wire and random wire antennas
However, early V3 units suffered from a critical design flaw: the JFET was connected directly to the battery voltage (Vcc_Bat) rather than the regulated radio voltage (Vcc_Radio), causing:
- Increased background noise and “birdies” (spurious signals)
- Excessive battery drain when the radio was off
- Units arriving completely discharged
2. Independent Headphone Amplifier
- Dedicated amplification circuit for the 3.5mm audio jack
- Significantly increased headphone volume
- Clearer audio output with better dynamic range
3. Antenna Input Protection
- Added diode protection circuitry at the antenna input
- Protection against static discharge and overvoltage
4. PCB Refinements
- Improved component layout
- Better power distribution
- Enhanced thermal management
Firmware Advancements
V3 introduced firmware version 2.28+ with substantial feature additions:
- WiFi Integration: Ability to connect to WiFi networks
- EiBi Schedule Database: Download shortwave broadcast schedules from EiBiSpace.de
- Enhanced Seek Sensitivity: Improved automatic station scanning
- RDS Support: FM Radio Data System information display
- Bandwidth Adjustment: Configurable IF bandwidth for improved selectivity
- AGC/ATT Control: Automatic Gain Control and Attenuator settings
- Soft Mute: Noise reduction during weak signal conditions
V3 Technical Specifications
- Audio Output: 1W speaker, amplified headphone jack
- Battery Life: ~10 hours typical use
- Casing: ABS plastic (improved rigidity over V1)
- PSRAM Support: Depending on specific board revision (QSPI or OSPI)
ATS MiniVersion 3S (V3S): The Refinement
The V3S was released as a stopgap to address the critical battery drain issue plaguing early V3 units.
JFET Power Routing Correction: The V3S corrected the JFET connection from the noisy, unregulated battery voltage to the clean, regulated Vcc_Radio rail. This single change resulted in:
- Elimination of the battery drain problem
- Reduced noise floor and fewer spurious signals
- Units shipping with charged batteries
- Improved overall receiver performance
- Through-hole mounting points corrected on PCB
- More robust assembly quality
- Same feature set as late-production V3 units
Important Note: Even V3S units benefited from the community-discovered modification to reroute the JFET power supply if they still exhibited the old connection pattern on certain board revisions.
ATS Mini Version 4 (V4): The Professional Grade Upgrade
Released in late 2025, the V4 represents the most comprehensive redesign of the ATS Mini platform.
Revolutionary Hardware Changes
1. Metal Alloy Casing
- Shift from plastic to metal (aluminum alloy) construction
- Internal RF shielding compartments
- Dramatically improved EMI/RFI immunity
- Better structural rigidity and premium feel
- Reduced susceptibility to interference from the ESP32’s digital circuits
2. Advanced PCB Design
- Complete board redesign with optimized RF sections
- Improved power supply filtering and regulation
- Better separation of analog and digital circuits
- Enhanced grounding scheme
3. Enhanced Audio System
- Improved headphone amplifier with even higher output
- Optimized speaker driver circuit
- Stereo channel support in some configurations
- Better frequency response and lower distortion
4. FM Earphone Antenna Mode When listening to FM, the V4 can use the connected earphones as an antenna, improving reception without requiring the telescopic whip antenna.
ATS Mini Version 4 :Advanced Features
Digital Modes Support:
- FT8 Decoding: Real-time decoding of FT8 digital mode transmissions
- FT4 Support: Faster variant of FT8
- CW Decoder: Morse code decoding and display
- RTTY Decoder: Radio teletype decoding
H.J. Berndt Firmware Support:The V4 hardware natively supports the advanced H.J. Berndt dual-core decoder firmware without requiring hardware modifications or soldering. This firmware provides:
- Multi-mode digital decoding
- Advanced DSP algorithms
- Enhanced user interface options
- Spectrum display features
ATS Mini V4 hardware revisions
The ATS Mini V4 family went through rapid hardware iteration, resulting in three closely spaced revisions: V4, V4a, and V4b. These versions are not clearly marked on the enclosure and can only be identified by inspecting the PCB, which has caused some confusion among users and reviewers. The original V4 and the intermediate V4a both suffered from a noticeable “theremin effect” in SSB mode, where touching or approaching the telescopic antenna caused audible frequency pulling due to PLL correction. This behavior was finally and properly cured in the V4b through improved grounding and RF layout.
Another change concerns the so-called “headphone antenna” function. In the first V4, the headphone cable could unintentionally act as an antenna and inject interference. The V4b redesign reduced this problem and added a small removable coaxial link at the headphone jack, allowing users to completely disable this feature if it proves troublesome in high-RF environments.
Finally, V4a and V4b introduced a routed connection from the Si4732 audio output to the microcontroller’s ADC (IO11), without requiring user modification. This hardware path is now used by the firmware for built-in CW and RTTY decoding and opens the door for additional digital modes in future updates. (Source – Peter Neufeld)
ATS Mini : Sensitivity Comparison
Independent testing by radio enthusiasts has shown:
V1 vs V3 (with MLA-30+ loop antenna): No discernible difference in sensitivity – the Hi-Z circuit provides no benefit with 50-ohm antennas, as expected.
V3 vs PL-330 (professional comparison baseline): The V3 achieves comparable sensitivity to the respected Tecsun PL-330, particularly on shortwave bands. This confirms the ATS Mini’s legitimacy as a serious receiver despite its tiny size.
V4 Performance: Reports indicate the V4’s shielded metal case and improved RF design provide:
- Reduced digital noise from the ESP32
- Fewer internally-generated spurious signals
- Better strong-signal handling
- Improved selectivity in crowded band conditions
Performance Comparison: Does the Metal Case Matter?
In side-by-side testing, the V4 outperforms the V3S in “noisy” environments. If you are using the radio near a computer or inside a house with lots of WiFi/LED interference, the V4’s metal shielding provides a significantly cleaner signal.
However, if you are out in a “quiet” field with a long-wire antenna, the V3S remains a powerful, budget-friendly champion that holds its own against professional receivers like the Tecsun PL-330.
The Future: V5 and Beyond
As of January 2025, AMNVOLT has officially stated that V5 is not in development. The team considers V4 to be sufficiently complete and plans to continue supporting it for at least 6-12 months before considering a V5. Any claims of V5 availability are fraudulent.
Possible future directions could include:
- Larger display options
- Integrated GPS for time synchronization
- Built-in signal strength logging
- Enhanced battery capacity
- Additional digital mode support
The ATS Mini series demonstrates how open-source hardware and active community involvement can drive rapid innovation. From the basic but capable V1 through the refined V3/V3S to the professional-grade V4, each iteration has addressed user feedback and pushed the boundaries of what’s possible in a pocket-sized receiver.
For most users in 2025, the V3S represents the sweet spot of features, performance, and value, while the V4 offers a premium experience for those who want the absolute best. Both versions benefit from excellent firmware support, active communities, and remarkable versatility in a package small enough to fit in a shirt pocket.
Whether you’re a shortwave listener, ham radio operator, or just curious about radio communications, the ATS Mini series proves that great things can indeed come in very small packages.
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