Unlocking NVIS Performance with the PolarFlip: Circular Beats Linear
The TerraBooster active loop-on-ground system is well-known for low-noise performance on the lower HF bands. But for NVIS (Near Vertical Incidence Skywave) work, its true potential is unlocked with our phasing hybrid: the PolarFlip.
What Is the PolarFlip?
Each TerraBooster provides a linear output from its shielded loop. Used alone, that already gives a clean, quiet signal with excellent CMRR. Place two loops side by side, connect them through the PolarFlip hybrid, and you unlock true circular polarization — selectable as LHCP or RHCP.
The PolarFlip is optimized for 1–8 MHz low-band work, covering 160 m through 30 m.
Outputs:
ANT1 – Linear output of loop 1
ANT2 – Linear output of loop 2
LHCP – Left-hand circular
RHCP – Right-hand circular
ANT1 and ANT2 are mainly for reference or for hunting down noise/QRM.
Why Circular Polarization Matters for NVIS
In NVIS, signals depart nearly vertically, reflect from the ionosphere, and return steeply. Faraday rotation scrambles polarization en route. A linear-only receiver suffers deep fades when polarization misaligns. PolarFlip solves this by letting you pick LHCP or RHCP instantly.
Benefits:
• Improved SNR: up to 6–12 dB simply by choosing the right hand
• Deep rejection: >10 dB suppression of opposite hand
• Consistent copy: less fading during rapid rotation
NVIS Optimization Tip: Research shows that in the northern hemisphere, RHCP often dominates from sunset to midnight. In the southern hemisphere, LHCP is more common. PolarFlip lets you flip instantly to follow it.
Rejecting Local Noise
Most man-made HF noise is linearly polarized. Combining loops in quadrature naturally rejects that linear interference, while enhancing circular skywave signals.
Real-World Results
• Biggest SNR gains on 160 m and 80 m
• Signals remain copyable even under strong QRM
• NVIS contacts 300–800 km away become much easier
Conclusion
The PolarFlip is more than a phase box — it’s a signal-to-noise weapon. Whether paired with TerraBooster, OctaLoop, or SkyTracer, two units plus a PolarFlip deliver circular reception and linear noise rejection for serious low-band NVIS.
Mini-FAQ
- Do I need two loops? — Yes. PolarFlip requires two matched loops for circular operation.
- Will it work on all HF bands? — No. It’s optimized for 1–8 MHz (160 m–30 m).
- Does it help for DX? — It’s aimed at NVIS, but can improve SNR in high-angle DX openings.
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