Proper Grounding and Choking to Eliminate Common Mode Noise in the Shack

When setting up your ham radio station, one of the most important but often overlooked aspects is effective grounding and common-mode current suppression. Looking from the shack perspective, the earth connection must be placed outside the shack, not inside. Here’s the recommended layout:

Why Outside Grounding is Crucial

  1. Avoiding Shack Re-radiation:
    If you place the earth connection inside the shack, common-mode currents (CMCs) can still flow on the outer shield of your coax and use your shack wiring or equipment as part of their return path. This creates RF hot spots in the shack and can cause RFI issues, both to your equipment and to other household devices.
  2. Choke Placement Is Key:
    The first choke, located immediately after the PA, blocks CMCs from exiting the shack via the coax shield. The second choke, placed right where the coax exits the building, ensures that any residual currents are forced to dump to ground outside the shack. The earth lug between these chokes ensures that unwanted RF energy has a low-impedance path to ground before the signal leaves the building.
  3. Safety and EMC Compliance:
    Grounding the shield outside enhances EMC (Electromagnetic Compatibility) and reduces the chance of electrical shocks caused by potential differences between equipment and ground. It also helps meet safety regulations, especially in lightning-prone areas.
  4. Cleaner Receiver, Quieter Station:
    Proper placement of chokes and an outside earth lug drastically reduce noise picked up by your antenna due to CMCs that would otherwise be reintroduced via shack wiring or ground loops.

Summary Layout:

[PA] -> [1st Choke] -> [Wall Feedthrough] -> [Earth Lug Outside] 
 ->[2nd Choke] -> [Earth Lug Outside] [Coax to Antenna] 
 ->[3th Choke at Antenna Base] -> [Earth Lug Outside]

This layout ensures that any common-mode energy is blocked at multiple stages and properly dumped to earth outside the shack, resulting in a cleaner, quieter station.

The earth lug on each choke should always face away from the shack. This applies to every choke up to the antenna. At the antenna, connect the choke to ground as well, and if the support structure is conductive, bond it to the same ground stake used for the choke.

Always remember: RF ground belongs outside, not in your shack!

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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.