Comparison of Active RX Antennas
In the world of receiving antennas, active designs are becoming increasingly important. They provide compact solutions with excellent performance, especially in environments with limited space or high noise levels. This article compares the active RX antennas currently available or in development within the RF.Guru lineup. The focus is on their frequency range, technical characteristics, and optimal applications.
Overview of the Antennas
| Antenna | Type | Frequency Range | Polarization | Coupling | Features |
|---|---|---|---|---|---|
| TerraBooster Maxi (release in 2025) | Shielded Loop | 160-80M | Horizontal | Magnetic Field | Balanced design, DC-grounded shield for extreme noise reduction |
| TerraBooster Medi (release in 2025) | Shielded Loop | 80-40M | Horizontal | Magnetic Field | Optimized for 80-40M, DC-grounded shield for noise reduction |
| TerraBooster Mini (release in 2025) | Shielded Loop | 40-20M | Horizontal | Magnetic Field | Smaller version for higher HF bands, DC-grounded shield for noise reduction |
| SkyScraper (release in 2025) | Active dipole (capacitively loaded) | 160-40M | Horizontal | Electric Field | 50cm dipole legs with 15cm capacitive disks at the ends, low-noise design with deep nulls |
| SkyScraper Maxi (release in 2025) | Active dipole | 40-10M | Horizontal | Electric Field | Wider design with 1m dipole legs, loses capacitive loading for higher frequencies |
| OctaLoop | Shielded Active Loop | 160M-30M | Horizontal | Magnetic Field | 1.2m diameter, shielded for noise reduction, excellent for lower HF bands |
| OctaLoop Mini (release in 2025) | Shielded Active Loop | 30-10M | Horizontal | Magnetic Field | 60cm diameter, shielded design for low-noise operation in higher HF bands |
| OctaLoop SubWave | Shielded Active Loop | 2200-600M | Horizontal | Magnetic Field | Specialized for VLF, 10-500 kHz range, shielded for noise rejection |
| EchoTracer | Active E-probe | 160-10M | Vertical | Electric Field | Height above ground determines band prominence, versatile across HF depending on mounting height |
| EchoTracer UltraWave | Active E-probe | 100MHz-1GHz | Vertical | Electric Field | Optimized for VHF, UHF, and SHF bands |
| Vertical Vortex (release in 2025) | Active E-probe | 160-80M | Vertical | Electric Field | Ground-mounted, 6m whip for enhanced low-band reception |
| GroundWeaver | Shielded Active Beverage-on-Ground | 160-10M | Horizontal | Electric Field | Highly directional, shielded for noise reduction, band depends on wire length |
Technical Comparison
Low RFI Performance
One of the biggest challenges in modern HF reception is radio frequency interference (RFI) from household electronics, power lines, and urban environments. Some antenna designs are inherently better at rejecting noise and minimizing external interference. The shielded loop antennas, such as the TerraBooster and OctaLoop series, excel in this regard. Their closed-loop design and shielding significantly reduce pickup of local noise, making them ideal for noisy urban or suburban locations. Similarly, the GroundWeaver uses a shielded Beverage-on-Ground concept, which also offers strong immunity to common-mode noise.
The shortened dipole design of the SkyScraper series, while balanced, is still prone to RFI due to its electric field coupling. The balanced nature helps in reducing common-mode noise but does not eliminate its sensitivity to environmental interference. Proper installation, orientation, and filtering techniques can mitigate these effects, but in high-noise environments, shielded loops remain the best choice for quiet and stable reception.
In contrast, E-field probes like the EchoTracer are more sensitive to environmental noise but compensate with their wideband coverage and compact size. When properly mounted away from noise sources and at optimized heights, they can still provide excellent results. For operators dealing with high RFI, shielded loops remain the best choice for quiet and stable reception.
Applications
- Longwave and VLF (10-500 kHz): OctaLoop SubWave
- Low HF bands (160-80M): TerraBooster Maxi, SkyScraper, GroundWeaver, OctaLoop, EchoTracer (low mounting), Vertical Vortex
- Mid HF bands (80-40M): TerraBooster Medi, SkyScraper, OctaLoop, EchoTracer (medium mounting)
- High HF bands (40-10M): TerraBooster Mini, SkyScraper Maxi, OctaLoop Mini, EchoTracer (high mounting)
- Lower HF bands (160M-30M): OctaLoop (standard 1.2m version)
- VLF and MF (2200-600M): OctaLoop SubWave
- VHF, UHF, and SHF (100 MHz - 1 GHz): EchoTracer UltraWave
NVIS and DX Performance
Different antennas excel in different operational modes. Near Vertical Incidence Skywave (NVIS) propagation is useful for regional communication, while low-angle reception is crucial for DX (long-distance) operation. The table below summarizes the optimal mounting height and performance of each antenna for NVIS and DX applications.
| Antenna | Best for NVIS (High-angle) | Height for NVIS | Short Skip DX | Height for Short Skip DX | Long Skip DX | Height for Long Skip DX |
|---|---|---|---|---|---|---|
| TerraBooster Maxi | Excellent | Near-ground | Good | Near-ground | Excellent | Near-ground |
| TerraBooster Medi | Excellent | Near-ground | Good | Near-ground | Excellent | Near-ground |
| TerraBooster Mini | Good | Near-ground | Moderate | Near-ground | Excellent | Near-ground |
| SkyScraper | Good | 10-12m | Moderate | 6-8m | Good | 8-10m |
| SkyScraper Maxi | Moderate | 10-12m | Moderate | 6-10m | Good | 8-12m |
| OctaLoop | Excellent | 2-5m | Good | 5-7m | Moderate | 6-8m |
| OctaLoop Mini | Good | 3-6m | Good | 6-8m | Moderate | 8-10m |
| OctaLoop SubWave | Not applicable | N/A | Not applicable | N/A | Not applicable | N/A |
| EchoTracer | Good (if low mounted) | 2-4m | Excellent (if medium height) | 4-6m | Excellent (if high mounted) | 8-12m |
| EchoTracer UltraWave | Not applicable | N/A | Not applicable | N/A | Not applicable | N/A |
| Vertical Vortex | Moderate | Ground-mounted | Good | 1-2m | Excellent | Ground-mounted |
| GroundWeaver | Excellent | Near-ground | Excellent | 10-15m wire length | Excellent | 20m+ wire length |
Conclusion
With this diverse range of active receiving antennas, operators can select the best solution for their operating conditions, whether for low-band DXing, noise mitigation, or wideband reception. Each antenna has unique advantages:
- Shielded loops ( OctaLoop, TerraBooster) excel in high-RFI environments and perform well for NVIS at low heights.
- GroundWeaver is ideal for both NVIS and DX, depending on the wire length.
- EchoTracer is highly flexible, especially when two units are used to cover the full HF range, making it effective for both NVIS (low height) and DX (high mounting).
- Vertical Vortex enhances DX operation, leveraging its 6m whip for better low-angle reception.
- SkyScraper dipoles, while balanced, remain more prone to RFI due to their electric field coupling but can still perform well with proper filtering and mounting height.
- SkyScraper Maxi is specialized for DX operation at higher HF bands.
Choosing the right antenna depends on the available space, noise conditions, and target frequency range.
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.