Your Transceiver Is Lying — The Hidden RF Path Nobody Told You About
Your SWR meter says “perfect,” but your radio’s case is still radiating. That’s because every transceiver, tuner, and SWR meter is unbalanced. One side of their RF output is tied to chassis ground — and that opens a hidden return path that most hams never think about.
Transmit: The Secret Return Path
During transmit, your PA expects equal and opposite currents on its output. But because the gear is unbalanced, part of that return sneaks onto the outside of your coax. These are stray return currents — the invisible RF that flows where it shouldn’t. They detune your antenna, shift feedpoint impedance, and turn the feedline into a radiator.
A 1:1 SWR doesn’t mean clean balance — it only means the inside of the coax looks matched.
Receive: The Noise Collector
When listening, the same path becomes a noise antenna. The coax shield picks up interference from your house wiring, routers, LED lights, and power supplies. These common-mode pickups travel straight into your receiver, masking weak DX signals under a bed of local noise.
Enter the Current Choke
A current choke (1:1 current balun) fixes both problems. It presents a very high impedance to those unwanted external currents while leaving the internal, differential RF untouched. On transmit, it forces all return current to stay inside the coax. On receive, it keeps the feedline quiet by blocking environmental noise from coupling back into your receiver.
How to Place It Right
- Mount the choke as close as possible to the antenna feedpoint.
- Use large ferrite cores — mix 31 for HF, mix 43 for upper HF/VHF.
- Wind multiple turns for wideband isolation and higher common-mode impedance.
- Add a second choke at the shack entry if you still notice RF feedback or high noise levels.
Don’t Confuse It With a Transformer
Most so-called “1:1 baluns” sold online are voltage-type transformers that match voltages but don’t stop unwanted currents. A true current choke provides isolation, not impedance transformation. It’s what keeps your system balanced and your feedline out of the radiation game.
The Takeaway
- Your transceiver’s output is unbalanced — one terminal tied to chassis ground.
- On transmit, this causes stray return currents on the outside of your coax.
- On receive, it turns into common-mode noise pickup.
- Only a properly placed current choke stops both — giving cleaner signals and quieter RX.
Mini-FAQ
- What’s the “hidden path” in my station? — It’s the unintended return current flowing on the outside of the coax and connected gear due to unbalanced design.
- Doesn’t a 1:1 SWR mean I’m safe? — No. SWR only describes the inside of the coax. You can have 1:1 SWR and still have heavy stray currents outside.
- Can a single choke fix both TX and RX issues? — Yes. It blocks stray return currents on transmit and noise pickup on receive.
- Where’s the best spot for it? — As close as possible to the feedpoint, and optionally another at the shack entry.
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