• RX 75Ω 1 kHz - 150 mHz +30dB CMR Optimized Line Isolator
  • RX 75Ω 1 kHz - 150 mHz +30dB CMR Optimized Line Isolator
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RF Guru

RX 75Ω or RX 50Ω 1 MHz - 30 MHz +50dB CMR Optimized Line Isolator

RX 75Ω or RX 50Ω 1 MHz - 30 MHz +50dB CMR Optimized Line Isolator

€197,00 EUR
€197,00 EUR
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Tax included.
Connector
Complementary: Stainless Steel (RVS / INOX 316) Mounting Kit available — use the small version for this choke.
All our products are handmade, and fulfilment times may vary depending on order volume. Please allow 2–3 weeks for your order to be completed and shipped.

This wideband common-mode choke is built for RX and low-to-medium-power HF applications where excellent isolation and corrosion resistance are essential. It combines three different ferrite types in series, each with 18 turns of thin 2–3 mm coax, to achieve exceptionally high choking across the LF–HF spectrum. Available in both 50 Ω versions (PL-259 or N-type) and 75 Ω versions with an F-connector for SDR or active-antenna systems.

Related reading:
Baluns in a Nutshell
Why “Common-Mode” Is the Most Abused Term in Ham Radio
How Much Choking Do You Really Need — for RX and TX?

Built for the Long Run

Instead of chasing power ratings, this model focuses on long-term reliability and environmental durability. Each enclosure is HV-coated internally and externally to prevent oxidation and galvanic corrosion, ensuring stable impedance over time — even in coastal or humid conditions. A polycarbonate housing with silicone gaskets provides full weather sealing, while the decompression valve balances pressure to prevent moisture ingress. Ideal for continuous outdoor installation next to active antennas, E-probes, or feedline entry points.

Installation Guidance

For best performance, install the choke as close as possible to the antenna feedpoint using a short jumper cable of 25 – 50 cm. This minimizes the RF voltage on the coax shield and stops common-mode current before it travels down the feedline. Adding a second choke at the shack entrance is strongly recommended — it keeps stray RF inside the shack where it belongs, preventing RFI from radiating along mains wiring or audio equipment. This two-stage isolation approach provides both cleaner reception and improved system stability.

Measured Common-Mode Performance

Conservative real-world figures verified using the Y-parameter common-mode method at RF.Guru Lab.

Region / Band Representative Frequency Choking |Z| (Ω) CMR (dB @ 50 Ω CM) CMR (dB @ 75 Ω CM)
ULF 1 kHz ≈ 36 Ω 4.7 dB 3.4 dB
VLF 10 kHz ≈ 360 Ω 18 dB 15 dB
LF 100 kHz ≈ 3.6 kΩ 37 dB 34 dB
MF 1 MHz ≈ 36 kΩ 57 dB 54 dB
HF Amateur Bands (Peak Choking)
160 m 1.9 MHz ≈ 25 kΩ 54 dB 51 dB
80 m 3.5 MHz ≈ 35 kΩ 57 dB 53 dB
40 m 7.0 MHz ≈ 50 kΩ 60 dB 56 dB
20 m 14.2 MHz ≈ 40 kΩ 58 dB 55 dB
15 m 21.2 MHz ≈ 30 kΩ 56 dB 52 dB
10 m 28.4 MHz ≈ 20 kΩ 52 dB 49 dB
All measurements are conservative and verified with three ferrite types in series, 18 turns per core, using 75 Ω coax.

Construction Highlights

  • Triple-ferrite design (three mixes in series) for wideband response
  • 18 turns per section using thin 75 Ω or 50 Ω PTFE coax
  • High-voltage coating inside and outside for anti-corrosion protection
  • Polycarbonate housing with precision-cut silicone gaskets for weatherproof sealing
  • Integrated decompression valve for pressure equalization
  • Connector options: PL-259, N-type (50 Ω) or F-connector (75 Ω)
  • All impedance and CMR values are conservative, verified under load
Technical Validation — Y-Parameter Method
All measurements are performed using the common-mode Y21 method with calibrated instrumentation. This approach directly measures current transfer through the choke rather than differential impedance, ensuring the quoted dB figures reflect real-world isolation of common-mode currents — exactly what determines receiver quietness and noise floor reduction.

Mini-FAQ

  • Q: Can I use this choke for transmit?
    — Yes, up to moderate power levels. For full QRO operation, use our dedicated high-power dual-core models.
  • Q: Is it waterproof?
    — Yes. The polycarbonate housing is gasket-sealed and equipped with a decompression valve.
  • Q: Should I install one or two chokes?
    — Ideally two: one close to the antenna with a 25–50 cm jumper, and another at the shack entry to stop stray RF from traveling along cables.
  • Q: What connectors are available?
    — PL-259 or N-type for 50 Ω systems, and F-connector for 75 Ω RX/SDR setups.
  • Q: Are the listed impedance values realistic?
    — Yes — all numbers are conservative, measured in-lab under realistic loading conditions.

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Written by Joeri Van Dooren, ON6URE — RF engineer, antenna designer, and founder of RF.Guru, specializing in high-performance HF/VHF antennas and RF components.
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