5 Game-Changing Upgrades for Your ATU 100 Antenna Tuner

As a ham radio enthusiast constantly looking to optimize my setup, I've discovered several modifications that dramatically improve the ATU 100's performance, durability, and usability. In this guide, I'll show you exactly how to upgrade your tuner from a basic unit to a showpiece of your ham radio station.

Whether you're a weekend operator or a serious DXer, these upgrades will help you get more reliable connections and better signal quality—all while giving your shack a more professional appearance.

Why the Stock ATU 100 Needs Upgrading

The ATU 100 automatic antenna tuner offers impressive functionality at its price point, but it comes with several limitations that can affect both performance and longevity:

• Inadequate RF shielding - The original plastic case provides virtually no protection against RF interference, which can affect tuning accuracy and potentially introduce noise into your signal path.
• Fragile SMA connectors - These small connectors weren't designed for frequent connect/disconnect cycles or heavier coaxial cables, making them a common failure point.
• Small display - The standard display is functional but difficult to read from a distance, requiring you to lean in close during operation.
• Basic button quality - The stock plastic button feels flimsy and doesn't match the quality of other ham radio equipment.
• Limited durability - Without proper protection, the internal components are vulnerable to damage from everyday handling and environmental factors.

After using the ATU 100 for several years, these limitations became increasingly apparent. Rather than replacing the entire unit, I decided to perform a series of targeted upgrades that would address each weakness while preserving the excellent core functionality.

Upgrade #1: Enhanced Metal Enclosure for Superior RF Shielding

The single most important upgrade you can make to your ATU 100 is replacing the original case with a metal enclosure. This modification delivers multiple benefits that directly impact performance:

I found an ideal metal case on AliExpress by searching for "aluminum project box." Look for dimensions of approximately 100mm × 100mm × 50mm to ensure adequate space for all components and upgrades. The aluminum construction offers an excellent balance of weight, strength, and RF shielding properties.

When transferring the circuit board to the new case, take care to use nylon standoffs to prevent any short circuits between the board and the metal case. This simple precaution will protect your investment and ensure reliable operation.

Upgrade #2: SO239 Connectors for Reliable Connections

The original SMA connectors are a significant weakness in the ATU 100 design, especially for permanent installations or when using standard-size coaxial cable. Upgrading to SO239 (UHF) connectors provides several advantages:

1. Remove the original SMA connectors using a soldering iron and desoldering pump or wick. Work carefully to avoid damaging the circuit board traces.
2. Prepare the case by drilling appropriately sized holes for the SO239 connectors. Use a step drill bit for clean, precise holes.
3. Mount the SO239 connectors securely to the case using the included nuts and lock washers.
4. Connect to the circuit board using 16-18 AWG solid copper wire, keeping the leads as short as possible to maintain impedance characteristics.
5. Establish a solid ground connection between each connector's flange and the circuit board ground plane. This is critical for proper RF performance.

This upgrade eliminates the need for SMA adapters, reduces connection losses, and provides a much more robust mechanical connection. The SO239 connectors are designed to handle the physical stress of repeated connections and disconnections, making them ideal for active ham operators.

Upgrade #3: 2.4-inch OLED Display for Enhanced Readability

The standard display on the ATU 100 works well enough but lacks visibility, especially in low light conditions or when operating from a distance. Upgrading to a larger 2.4-inch I2C OLED display dramatically improves the user experience:

I recommend the HiLetgo 2.42" OLED display module, which offers excellent brightness, contrast, and viewing angles. The white-on-black display is particularly easy to read in all lighting conditions, and the I2C interface makes connection straightforward with just four wires.

To install the new display:

1. Carefully measure and mark the display cutout on your new enclosure
2. Use a Dremel tool with a cutting wheel to create the opening
3. Clean the edges with a file and test-fit the display
4. Connect the display to the I2C pins on the ATU 100 board (SDA, SCL, VCC, and GND)
5. Secure the display with small screws or adhesive standoffs

For a professional finish, consider adding a thin clear acrylic cover or 3D-printed bezel around the display opening. This not only improves appearance but also protects the display from damage.

Upgrade #4: Premium Aluminum Tuning Button

The original plastic button on the ATU 100 feels out of place alongside more premium ham radio equipment. Replacing it with a high-quality aluminum button improves both aesthetics and functionality:

Look for a momentary push button with a metal finish that complements your enclosure. The ideal replacement has a positive tactile feel and requires just enough pressure to prevent accidental activation without being difficult to press.

This seemingly small upgrade has a surprisingly significant impact on the overall user experience. The solid feel of a quality button provides tactile feedback during operation and contributes to the professional appearance of your modified tuner.

Upgrade #5: Improved Grounding for Enhanced Performance

A proper grounding system is crucial for optimal tuner performance yet often overlooked. When rebuilding your ATU 100 in the new enclosure, take the opportunity to implement comprehensive grounding:

• Create a direct ground connection between the SO239 connector flanges and the metal case
• Add copper braid straps between the circuit board ground plane and the case
• Ensure all mounting screws make good electrical contact with the case by removing paint or anodizing at contact points
• Add a dedicated external ground lug connected directly to the case for station grounding

These grounding improvements reduce common-mode currents, minimize RF feedback, and generally result in cleaner, more reliable tuning performance. The difference is often most noticeable when operating at higher power levels or on challenging bands like 160 meters.