The Future of RX: aRFoF vs Coax in QRM-Challenged Environments

Why Analog RF over Fiber is the Superior Feedline for Long-Distance RX Chains Below 50 MHz

In today’s RF landscape, high levels of man-made noise (QRM) make it increasingly difficult to maintain clean receive paths—especially on the low bands like 160 m, 80 m, and 40 m. Long coaxial runs to remote antennas often become part of the noise problem, not the solution.

Enter analog Radio Frequency over Fiber (aRFoF): a modern, noise-immune alternative to coax that delivers pristine analog RF signals over 100+ meter distances without the QRM baggage.

Loss and Performance Comparison Over 100 Meters

Let’s compare RG6 coaxial cable with 50/125 µm multimode fiber using an aRFoF link, focusing on the sub-50 MHz range:

Parameter RG6 Coax (75 Ω) aRFoF (50/125 µm MM Fiber)
Frequency range 1 – 3 GHz 1 – 50 MHz
Signal type Analog RF Analog RF
Attenuation over 100 m ~2.6 dB @ 30 MHz < 0.3 dB (optical + electronics)
EMI susceptibility High None
Ground loop risk High None (galvanic isolation)
Common-mode pickup Significant None
Capacitance loading Medium–high Negligible
Line cost per meter €0.30–0.50 ~€1.50–2.00
System complexity Low Moderate (requires optoelectronics)
Return loss/SWR effects Present None (impedance decoupled)
Maintenance Minimal Requires clean optics

💡 Key takeaway: aRFoF outperforms coax in every metric for long-distance RX—especially in noisy environments.

QRM Immunity: Fiber Changes the Game

Unlike coax, which is susceptible to:

  • Radiated EMI from Ethernet, switch-mode PSUs, LED lighting
  • Conducted RF noise from power systems
  • Ground loops and potential differences

Fiber is completely dielectric and immune to all of the above. No conducted noise. No induced signals. No common-mode currents. It’s the ultimate “invisible link” between your antenna and receiver.

This is particularly critical when working with:

  • Active antennas (e.g., EchoTracer, E-probe designs)
  • Remote loop or vertical arrays
  • Low-band DXing, where QRM often dominates weak signals

How aRFoF Works

Here’s a typical receive chain using aRFoF:

  • Antenna (passive or active) captures the RF signal
  • aRFoF Transmitter Module converts the analog RF into modulated light
  • Multimode Fiber Cable transports the signal over 100–500+ meters
  • aRFoF Receiver Module demodulates the light back to analog RF
  • Receiver (SDR, analog RX, spectrum analyzer) processes the clean signal

📌 aRFoF preserves real-time analog phase and amplitude information — essential for direction finding, diversity RX, and beamforming systems.

Ideal Applications for aRFoF

  • Remote RX antennas 100+ meters from the shack
  • QRM-heavy environments where coax picks up unwanted noise
  • Receive-only phased arrays
  • Shared receive sites between operators or RX farms
  • Active antenna deployments, where common-mode rejection is critical

A Real-World Example

Using RG6 for a 120-meter run to a low-noise vertical on 160 m? Expect up to 3–4 dB of loss and significant QRM ingress unless heavily choked and shielded.

Replace that link with an aRFoF chain, and:

  • Signal-to-noise improves drastically
  • Band edges become clean
  • QSB and weak DX become more discernible

All without touching the antenna.

Soon Available from RF.Guru

aRFoF modules are currently under development at RF.Guru, tailored for sub-50 MHz analog RX applications. These compact modules will feature:

  • Bandwidth from 100 kHz to 50 MHz
  • Optimized for active antennas and low-level RX signals
  • Low-noise design with adjustable gain
  • Compatible with standard 50/125 µm multimode fiber
  • Powered via coax or local bias-T

Whether you're building a remote phased array or isolating an EchoTracer from shack noise, these modules will offer a plug-and-play path to fiber-fed receive excellence.

📡 ETA: Q2 2026. Interested in beta testing? Contact us at RF.Guru.

Conclusion

As QRM continues to rise and RX antennas are pushed farther from the shack, coax becomes more of a liability than a solution. For serious RX work below 50 MHz, analog RF over fiber is the new standard.

With RF.Guru’s upcoming aRFoF modules, you'll soon be able to deploy ultra-clean, QRM-immune RX chains without the noise headaches of coaxial feedlines.

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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.