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

Why Analog RF over Fiber is the Superior Feedline for RX Chains Below 10 MHz (Even at Short Distances)

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 and 80 m. Even relatively short coaxial runs to remote antennas can 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 distances up to 10 meters using plastic optical fiber (POF), without bringing QRM along for the ride.

aRFoF vs. Coax at 10 Meters: A Focus on Low Bands

Let’s compare a typical RG6 coaxial cable with a plastic optical fiber–based aRFoF link for the 1–10 MHz range:

Parameter	RG6 Coax (75 Ω)	aRFoF (1 mm POF, analog)
Frequency range	Up to 3 GHz	1 – 10 MHz
Signal type	Analog RF	Analog RF
Attenuation @ 10 m	~0.26 dB @ 7 MHz	< 0.1 dB (optical + electronics)
EMI susceptibility	High	None
Ground loop risk	High	None (fully isolated)
Common-mode pickup	Significant	None
Capacitance loading	Moderate	Negligible
Line cost per meter	€0.30–0.50	~€1.00–1.50
Return loss/SWR	Present	None (impedance decoupled)
Maintenance	Minimal	Requires clean optics

🔎 Key takeaway: Even at 10 meters, aRFoF outperforms coax for noise-sensitive RX work—especially on the low bands, where common-mode rejection becomes harder to achieve.

QRM Immunity: Fiber Solves the Root Problem

Unlike coax, which is vulnerable to:

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

POF is completely dielectric and immune to all of these. No conducted noise. No induced signals. No common-mode currents. It's the perfect invisible link between your antenna and receiver.

This matters most when working with:

• Active antennas (EchoTracer, E-probe, Octaloop, etc.)
• Remote receive elements in compact phased arrays
• Low-band DXing where man-made noise dominates

How aRFoF Works at 1–10 MHz

A complete aRFoF RX chain looks like this:

• Antenna (passive or active) captures the RF signal
• aRFoF TX module converts analog RF into intensity-modulated light
• Plastic optical fiber (POF) carries the signal (up to 10 m)
• aRFoF RX module restores the analog RF for direct receiver input
• Receiver (SDR, analog, or spectrum analyzer) processes a clean signal

Unlike digital links, aRFoF preserves real-time amplitude and phase — essential for beamforming, phasing, and signal purity.

Hybrid Deployment: Combining RG6 and POF for 300m RX Links

In situations where a receive site is located several hundred meters away (e.g., a forested area 300 m from the shack), a hybrid feedline approach can offer the best of both worlds:

• Use RG6 coax for the first 200–300 meters to bring RF back toward the shack. Loss is manageable (~1.6 dB at 7 MHz over 200 m), especially if preceded by a low-noise amplifier.
• Just outside the shack, transition to aRFoF over a 10 m POF link to eliminate common-mode pickup and local QRM.

By placing the aRFoF transmitter in a shielded outdoor utility box, you can run a 10 m coaxial cable (for DC power) and a 10 m POF cable in a single conduit to the shack. This removes the need for long coax runs through QRM-heavy environments, and keeps the sensitive fiber run short and effective.

This hybrid solution:

• Leverages coaxial cable's long-range practicality
• Preserves aRFoF's excellent noise immunity near the operating position
• Simplifies deployment using common conduit layouts

Ideal Use Cases at Short Range

Even if you’re only isolating an antenna 5–10 m from your shack, aRFoF solves key problems:

• QRM immunity for low-band RX
• No coaxial pickup or common-mode
• Galvanic isolation, removing ground loops
• Low-loss analog path for high-SNR reception

A Real-World Comparison

Using 10 meters of RG6 coax to connect an active antenna like the EchoTracer?
Expect 0.2–0.3 dB of signal loss — and much worse, the coax may carry in noise from:

• Your shack’s Ethernet switch
• A noisy USB wall wart
• Ground current between your gear and antenna ground

Replace it with a 10 m aRFoF link, and:

• Signal-to-noise improves instantly
• Weak signals on 160 m or 80 m become copyable
• No choke placement or balun experimentation needed

Coming Soon from RF.Guru

We're actively developing compact analog aRFoF modules optimized for the 1–10 MHz RX band. These plug-and-play units will feature:

• Full analog bandwidth from 100 kHz to 10 MHz
• Designed for use with 1 mm POF (plastic optical fiber)
• Optimized for active antennas and low-signal work
• Extremely low noise floor with optional gain control
• Powered over coax or local bias-T

📡 Target availability: Q4 2026
Want to beta test the modules? Let us know at https://rf.guru

Final Thoughts

For serious low-band receive work — especially in high-QRM environments — coaxial cable is often more of a liability than a solution.

Even over just 10 meters, analog RF over fiber delivers:

• Clean signal paths
• Zero common-mode currents
• No EMI pickup
• Lossless performance from antenna to receiver

By combining coax for long-haul transmission and fiber for final-stage isolation, operators can now build 300 m noise-free RX paths that preserve signal integrity all the way to the shack.

RF.Guru’s aRFoF modules will soon let you deploy professional-grade, noise-immune receive paths — even in the noisiest of shack environments.

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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.