SD9-400

The SD9-400 is an ultra-high-performance TETRA Band Stacked Dipole Array engineered for elite base station applications in the 380–420 MHz range. Featuring eight vertically stacked folded dipoles, this heavy-duty array is designed for highly populated radio sites that demand long-haul coverage and high-power handling. With its unique field-adjustable radiation pattern, the SD9-400 provides a versatile solution for TETRA, repeater, and paging systems, ensuring constant gain and low VSWR across its entire 40 MHz bandwidth.

Design: Field-Adjustable Radiation Patterns

The SD9-400 offers unparalleled flexibility with a radiation pattern that can be reconfigured in the field using standard hand tools. When the eight dipoles are arranged 90 degrees apart around the central mast, the system produces a powerful 9 dBd omni-directional pattern. Alternatively, by aligning all eight dipoles collinearly in a single direction, the array achieves a 12 dBd offset radiation pattern for targeted long-distance coverage. This "null-filling" capability ensures that signal gaps are eliminated, providing consistent, high-quality audio and data transmission throughout the coverage area.

Construction: Engineered for Site Longevity

Built to withstand the harshest environmental stressors, the SD9-400 is constructed from 6063T6 architectural anodized aluminum. Each of the eight folded dipoles is fed in phase via a specially designed center-fed phasing harness. To prevent weather-related degradation and RF inter-modulation, all cable connections and dipole ends are sealed in high-grade epoxy. The phasing harness features molded power splitter joints to minimize signal loss, while the molded N-Female termination ensures complete waterproofing for the primary feed point.

Reliability: High-Power Tactical Protection

With a massive 500 Watt RF power handling capacity, the SD9-400 is ideal for high-traffic network hubs. The antenna is designed for ultimate lightning protection, operating at D.C. ground to provide a low-resistance discharge path through its high-strength aluminum tubular boom. For logistical ease, the 6-meter central mast is shipped in two 3-meter sections. All fasteners are made of Type 316 marine-grade stainless steel, ensuring that the array remains structural and functional during extreme weather events and wind speeds up to 200 Km/Hr.

Technical Features

• Adjustable Gain Configuration: Switch between 9 dBd Omni-directional or 12 dBd Offset patterns depending on site requirements.
• Eight-Element Stacked Array: Precision-engineered vertical stacking delivers a tight 9-degree vertical beamwidth for maximum horizon reach.
• Ultra-Wide 40 MHz Bandwidth: Maintains constant gain and VSWR across the entire 380–420 MHz TETRA spectrum.
• 500W High-Power Capacity: Heavy-duty electrical design supports high-duty cycle transmissions for repeaters and multi-channel hubs.
• Molded Phasing Harness: Eliminates connectors and adapters within the harness to minimize loss and prevent moisture ingress.
• 6063T6 Anodized Aluminum: High-strength architectural alloy provides superior corrosion resistance in industrial environments.
• Integrated Lightning Protection: D.C. ground design protects sensitive base station electronics from atmospheric discharges.
• Modular 6-Meter Mast: Shipped in two sections for simplified handling and lower shipping costs.
• Marine Grade SS Fasteners: All hardware is made of 316 stainless steel for maximum longevity in coastal or humid regions.
• Field Configurable: Allows for pattern adjustment on-site without the need for specialized factory equipment.

Stacked Dipole Array Configuration Guide: Omni-Directional vs. Offset Patterns

The SD9-400 is a versatile "pattern-shaping" antenna. Unlike fixed-radome collinear antennas, a stacked dipole array allows the installer to physically manipulate the orientation of the elements to match the specific geographic needs of the radio site.

1. The Omni-Directional Configuration (9 dBd Gain)

When the eight dipoles are arranged in a cloverleaf pattern (staggered 90 degrees apart around the central mast), the antenna produces a balanced, circular radiation pattern.

• Best For: Centrally located base stations in urban areas, industrial campuses, or flat plains where users are scattered in all directions (360-degree coverage).
• The 9 dBd Advantage: By spreading the energy evenly, you ensure no "blind spots" exist within the network. The vertical stacking of eight elements still provides a very tight 9-degree vertical beamwidth, ensuring the energy is pushed toward the horizon rather than wasted on the sky or the ground.

2. The Offset/Directional Configuration (12 dBd Gain)

By aligning all eight dipoles collinearly (pointing them all in the same direction), the array transforms into a high-intensity directional antenna.

• Best For: Corridor coverage (highways, railways, or pipelines), coastal sites looking inland, or "edge-of-network" base stations that need to push signals deep into a specific territory.
• The 12 dBd Advantage: This configuration yields an additional 3 dB of gain over the omni pattern—effectively doubling the perceived signal strength in the favored direction. It creates a broad forward lobe that covers roughly 160–180 degrees horizontally while significantly suppressing radiation to the rear.

3. Center-Fed Phasing & Signal Integrity

The "brain" of the SD9-400 is its center-fed phasing harness. In many stacked arrays, signal delay (phasing error) can cause the beam to "tilt" or "squint" away from the horizon.

• In-Phase Distribution: The SD9-400 harness ensures that the RF signal reaches all eight dipoles at the exact same microsecond. This forces the eight individual waves to merge into a single, powerful wave front that stays perfectly parallel to the ground.
• Molded Reliability: Because the power splitters are molded and sealed, there are no internal connectors to vibrate loose or allow moisture ingress, which is the #1 cause of "crackle" (PIM) and signal degradation in older dipole arrays.

4. Mechanical Stability & Lightning Hardening

At 6 meters (19.7 feet) in length, the SD9-400 is a significant structure.

• Lightning Path: Every dipole is directly clamped to the high-strength 6063T6 aluminum mast. In the event of a strike, the mast acts as a massive lightning rod, shunting the current directly to the tower ground and bypassing the delicate phasing harness and base station electronics.
• Wind Shedding: The "open" design of a dipole array allows wind to pass through the structure with much less resistance than a solid fiberglass radome of the same height. This reduces the "overturning moment" on the tower, which is critical for sites prone to high-velocity wind gusts.

Installation & Optimization Checklist

• Mast Verticality: With a 9-degree vertical beamwidth, a mast that is only 3 degrees out of plumb will shoot the signal into the ground on one side and into the sky on the other. Use a professional transit or high-precision level.
• Side-Mount Offset: If mounting to the side of a large tower, use the 1.35-meter horizontal arms. Mounting the dipoles too close to a wide steel tower will cause the metal to act as an unintended reflector, distorting your omni-directional pattern.
• Torque & Sealing: While the phasing harness is molded, the primary N-Female input must be hand-tightened and then sealed with a professional weatherproofing kit (butyl and vinyl tape) to prevent moisture wicking.
• Field Reconfiguration: If the site's requirements change (e.g., a new station opens nearby and you no longer need 360-degree coverage), you can simply loosen the U-bolts and re-align the dipoles into the 12 dBd Offset position without removing the mast from the tower.