Why You Need At Least Three Chokes in Your Antenna System

As a ham operator, you've probably heard of common mode currents (CMC)—but too many setups still completely lack proper choking. Every day I see antenna installations with no choke at all, or at best, just one. That's a recipe for a noisy shack, RF feedback, weird SWR readings, and even gear damage.

Let’s break down why three well-placed chokes should be the new baseline in your HF setup.

What’s a Choke, Really?

A choke—typically a common mode current choke—is a device that blocks unwanted RF current flowing on the outside of the coax shield. These currents cause all kinds of issues:

• High noise levels on receive
• RF in your shack (literally!)
• Unreliable SWR measurements
• Interference with electronics
• Risk of RF burns or damaging your radio

Choke #1: At the Antenna Feedpoint

This is the most obvious one, and still often overlooked.

Why it's needed:

• Prevents the coax shield from becoming part of your radiating system
• Ensures the antenna pattern remains predictable
• Reduces RF picked up by the coax acting as a long-wire antenna
• Minimizes the skin effect imbalance, where RF current prefers the outer surface of the coax braid, leading to undesired radiation and coupling

Use case:

• End-fed half-wave? Place a choke at about 0.05 λ after the 49:1 UNUN.
• OCF dipole? Add one after the 4:1 UNUN. If the counterpoise is formed by the coax, it will typically balance around ±⅓ of the feedline length—check carefully before placement.
• Verticals? Even more critical to kill coax-induced radiation.

Choke #2: Before the Coax Enters the Building

This is your line of defense to keep the RFI outside.

Why it’s needed:

• Prevents RF from coupling into your shack wiring
• Keeps noise picked up by the feedline from entering your radio environment
• Minimizes risk of RF feedback or triggering strange PC/audio behavior

Bonus tip:

Add a grounding lug here with a short strap to a real ground rod. For RF purposes, a higher-resistive path (for example RVS stainless rather than pure copper) is best. Do not connect a PE earth wire to this RVS rod — it is meant solely as a controlled bleed path for common mode currents and static, not a mains safety earth.

Choke #3: At the Shack End (Just Before the Rig, Tuner, or Amp)

This is your last and most personal line of defense.

Why it’s needed:

• Protects your transceiver from stray RF
• Helps eliminate RF in audio, CW keying problems, digital mode glitches
• Keeps your hands and equipment safe
• Limits ingress of locally generated noise from shack equipment (PCs, routers, switch-mode PSUs) that can couple back via small coax imbalances

Think of this one as your "insurance choke"—even if your other two do their job, this one protects you from anything that slips through.

The Benefits Are Real

After installing these three chokes, users typically report:

• A lower noise floor (sometimes by several S-points!)
• More consistent and repeatable SWR curves
• Less “strange behavior” when transmitting
• A cleaner signal and better reports
• Peace of mind that RF is where it should be—outside the shack

Bonus: What Kind of Choke Should You Use?

• Use ferrite chokes (type 31 for broadband)
• Wind coax through toroids or use high-quality premade choke baluns

Don’t Let RF Rule Your Shack

One choke is better than none. Two is good. But three is ideal—antenna, building entry, and shack entrance. They work together to keep RF out of places it shouldn't be.

Treat your feedline like a highway for signals—don’t let stray traffic get off at the wrong exits.

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