The Use of INOX Stakes as High Impedance Termination Points for RX Shielding and EFHW Counterpoise

In the world of HF (High Frequency) reception and end-fed antenna design, particularly below 30 MHz, unconventional methods are sometimes employed to achieve specific design goals. One such practice involves using stainless steel (RVS / INOX) stakes as high impedance terminations, either for grounding the shield of a coaxial cable in a receive-only setup or as a counterpoise in end-fed half-wave (EFHW) antennas. This approach often raises eyebrows in the ham radio community, as stainless steel is not generally regarded as an ideal conductor. So, is this method valid, or are the skeptics correct?

Understanding the Application Context

The criticism typically arises from comparing stainless steel to copper in traditional RF grounding or transmission applications. Copper is preferred due to its low resistivity and excellent RF conductivity, especially in the context of safety grounds and RF current return paths where skin effect dominates.

However, in the specific context of this article — receive-only setups and counterpoise designs where high impedance is desired — the requirements differ substantially:

  • We're not aiming for a low-impedance RF ground as in a transmission scenario.
  • We're not dealing with high current, but instead with voltage nodes in EFHW antennas or RF potential isolation.
  • We're intentionally avoiding strong coupling to ground, instead using a high impedance termination to limit unwanted RF return currents.

INOX as a High Impedance Element

Stainless steel, due to its higher resistivity compared to copper or aluminum, exhibits significantly higher impedance at RF. While this makes it a poor choice for conductive elements where current flow is desired, it may be a useful characteristic when designing systems where blocking or reducing RF current is the actual objective.

Applications

  1. RX Shield Grounding Blockade: In receive-only applications using active antennas like E-probes or active whips, connecting the shield of the coax to an INOX stake can serve as an impedance choke — bleeding off static but not forming a low-Z RF path to ground. This can reduce common mode pickup without providing a full RF ground. (less noise!)
  2. High-Z Counterpoise in EFHW: For end-fed half-wave antennas, especially when no full radial system is possible, an INOX stake can act as a virtual counterpoise — providing a termination with high impedance to ground, helping balance the system without introducing strong return currents that could flow into the coax shield.
  3. Baluns with Ground Lugs: For baluns that include a ground lug, an INOX stake can be a suitable connection point. The high impedance to ground it presents — even under poor soil conductivity conditions — helps reduce unwanted RF feedback without strongly grounding the system.

What INOX is Not Suitable For

It's important to note that INOX stakes are not universally applicable. For applications where a true low-impedance ground is needed — such as:

  • Balanced line bleeder systems that require effective dissipation of common mode current,
  • Mast safety grounding for lightning protection or equipment safety,

... a stainless steel stake is not appropriate. In these cases, copper or galvanised ground rods with good earth contact and lower resistivity are mandatory to ensure safety and performance.

⚠️ Note: To prevent ground loops when low-impedance bonding to the protective earth of your home is not possible, maintain a minimum distance of 15–20 meters between independent ground rods or ground systems. This reduces circulating current and potential differences during lightning events or high RF power operation.

Product Examples from RF.Guru

At RF.Guru, we offer several grounding solutions tailored to the specific needs outlined above:

Comparing to Copper or Galvanized Steel

Using copper for the same task might over-ground the system, leading to increased common-mode currents in the coax or undesired radiation patterns. INOX provides a weak capacitive link to true ground with resistive dissipation of static and some RF, but not enough to dominate the system behavior.

Galvanized steel is a closer match in impedance to stainless but tends to degrade faster and isn't as corrosion-resistant, making INOX a more stable long-term choice.

Measurement

In this test setup, a common-mode signal was injected at the top of an RVS stake using a Tekbox current probe. A bulkhead adapter was mounted directly onto the RVS stake, which was inserted into normal earth to ensure realistic grounding conditions. The objective was to evaluate the common-mode impedance presented by the RVS stake in conjunction with its earth contact.

A second Tekbox current probe was placed at the output side to measure the remaining common-mode current.

The results show strong attenuation at lower frequencies — exceeding 30 dB at 1.8 MHz and remaining above 15 dB up to 10 MHz — demonstrating effective suppression of common-mode currents in the HF band.

At higher frequencies (above 20 MHz), attenuation decreases to around 3–7 dB, which aligns with expectations as capacitive coupling and wavelength effects become more dominant.

These results confirm that an RVS stake with direct earth contact and integrated bulkhead provides high common-mode impedance, making it highly effective for RF grounding and feedline isolation in antenna systems.

Conclusion: Myth or Valid Approach?

In this niche use case, INOX stakes are a valid engineering solution, not a compromise born of ignorance. While unsuitable as a ground for high power or transmission lines, they serve a unique role when high impedance, corrosion resistance, and stability are more important than conductivity. This makes them ideal for:

  • Blocking or reducing unwanted RF currents in receive setups.
  • Acting as high impedance counterpoise elements in EFHW systems.
  • Providing high-Z ground references for baluns in poor soil conditions.

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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.