TerraBooster: High-CMRR Active Loop for Urban HF Reception
The TerraBooster is an advanced active loop antenna system designed to deliver uncompromised HF reception performance in high-interference urban environments. Electrically, it shares the same proven push-pull amplifier core as the OctaLoop, but its defining feature lies in the physical scale and feed architecture.
Massive Loop Geometry
At the heart of the TerraBooster is a 56-meter shielded loop configured in a square formation and fed in one corner. This large perimeter gives the loop high magnetic sensitivity, low effective height loss, and a significant advantage in signal pickup over smaller loops.
Shielded Coaxial Receiving Element
The loop is built entirely from shielded coaxial cable, with the shield itself acting as a Faraday cage. To mitigate the elevated risk of common-mode pickup over such an extended shield length, the coax shield is terminated to ground via an RC network at the feedpoint. This acts as a broadband drain path for any residual shield currents without shorting RF signals of interest.
The result is a significant reduction in common-mode coupled noise, particularly from switching supplies, PLC emissions, and household EMI, which are prevalent in densely populated areas.
Architecture and Amplifier
- Loop Geometry: Square loop, 56 m circumference
- Amplifier Core: Dual MMIC in true push-pull
- Transformer: Center-tapped 1:1.5 for balanced input
- Power Injection: Via common-mode filtered coax (two-stage)
- Output Balun: High Impedance choke with balanced output
Performance Characteristics
| Parameter | Value |
|---|---|
| Frequency Range | 100 kHz – 30 MHz |
| Loop Perimeter | 56 meters |
| Amplifier Architecture | Push-pull, differential |
| Shielding Effectiveness | > 60 dB |
| Common Mode Suppression | Enhanced via shield RC grounding |
| Output IP3 (OIP3) | +41 to +43 dBm (depends on receive element) |
| P1dB | > +19.5 dBm |
| Noise Figure | ~1.7 dB |
| Supply Current | ~160 mA |
| Output Impedance | 50 ohms |
Urban Optimization: Beyond Standard CMRR
Traditional loop antennas already enjoy inherent common-mode rejection due to their differential geometry. The TerraBooster, however, goes further:
- Its sheer physical scale increases exposure to unwanted electric fields and EMI
- The coax shield over the full 56-meter length would normally act as a pickup for conducted interference
- This is countered by the grounded RC drain on the shield, which bleeds off common-mode energy across a broad frequency range
This is not just CMRR at the amplifier level, but whole-system common-mode suppression — from loop geometry to shield termination, to balanced-to-unbalanced transformation.
Use Cases
The TerraBooster is ideal for:
- Urban and suburban installations with high QRM
- DXing across 160m to 10m with minimal E-field contamination
- Long-term monitoring or recording systems requiring stable, quiet HF input
- Applications where antenna placement is close to buildings, power lines, or digital infrastructure
- Good companion for our PolarFlip (LHCP and RHCP for HF)
Conclusion
The TerraBooster brings the high-dynamic range architecture of the OctaLoop to a grander scale, enhancing reception with improved CMR, physical loop gain, and shielding strategy. If you're battling urban noise but have the space for a large perimeter loop, the TerraBooster is your best defense against HF pollution.
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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.