RF Grounding in an Apartment: Counterpoise, Radials, and Artificial Grounds That Work
Why apartment antennas have no earth ground and what replaces it: counterpoise wires, radials, and artificial ground tuners that cure RF in the shack.
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You put up an end-fed, got on air, and now the mic is hot to the touch, the SWR meter bounces randomly, and every time you key down the USB audio interface drops out. Or the SWR looks fine but you are not making contacts you should be making. The diagnosis in both cases is usually the same: your antenna has no return path for RF current, so it found one on its own, and what it found was you, your desk, and your mains wiring.
That is the RF grounding problem in an apartment. This is the engineering treatment.
Three Things Called "Ground" (Only One of Which Matters Here)
The word "ground" gets used for three distinct electrical functions, and confusing them is the fastest way to make this problem worse.
AC safety ground is the green wire in your wall outlet. It exists to trip a breaker if a live wire contacts a chassis. Shock protection only. Routing RF through it couples your signal into every appliance on that circuit. It is not your RF return path.
Lightning and bonding ground protects equipment from transient surges. A real lightning ground requires a copper rod driven into earth. On the third floor of a wood-frame building, this is not available to you.
RF ground / counterpoise is the electrical return path for RF current: the missing half of the antenna. A vertical is half a dipole; the radials or ground plane below it are the other half. A random-wire or end-fed needs the same thing. Without a return path, the RF current goes looking on its own. This is the one this article is about.
What "RF in the Shack" Actually Means
When your antenna has no defined RF return path, the current flows where it can: the outside of your coax braid, the shack wiring, the computer chassis, the USB cable to your interface, and you. You are touching the mic or the PTT switch, you are connected to the desk through your arms, and that makes you part of the circuit.
A hot mic means RF current is flowing on the microphone chassis. Erratic SWR means the counterpoise is changing as you shift in your chair or move the coax. USB dropouts happen because RF on the cable induces voltage into the logic signals. None of this is a radio defect. It is a circuit topology problem.
Counterpoise vs. Radials: What Each One Does
A counterpoise is a single wire connected to the "cold" side of the antenna feed point: the ground terminal of the transformer in an end-fed, or the coax connector body on a vertical. It presents a controlled RF impedance so current flows on the wire rather than on the coax shield or the chassis. A quarter wavelength on the band of use makes it resonant and presents a low impedance. For multiband use, either cut it for your most-used band or use an artificial ground tuner (see below) to tune it across bands.
Radials are multiple counterpoise wires, typically for a vertical. Forget ground-mounted radial fields entirely for a balcony. What IS practical is two to four elevated quarter-wave wires at the feed point, bent to fit the space. Elevated radials are more efficient than ground-mounted ones when you only have a few. Two resonant elevated radials outperform twenty buried ones.
| Configuration | How many wires | Where they go | Apartment practical? |
|---|---|---|---|
| Single counterpoise (EFHW/random wire) | 1 | Along baseboard, out to balcony | Yes, very practical |
| Elevated radials (vertical) | 2-4 per band | Horizontal from feed point | Yes, balcony with rail |
| Ground-mounted radial field | 32-120 | Buried in earth | No |
| Earth ground rod | 1 + bond wire | Driven into soil | No (upper floor) |
For an EFHW or random-wire at your window, a single 16-foot counterpoise (quarter wave on 20m) tucked along the baseboard or window trim eliminates most RF-in-the-shack symptoms on 20m and higher. For 40m you want roughly 33 feet, harder to route but doable along two walls. For a balcony vertical, two quarter-wave wires clipped to the feed point and draped over the rail do the job.
The Artificial Ground Tuner
An artificial ground tuner is a variable L-C network between the radio's ground terminal and a counterpoise wire. The classic is the MFJ-931 Artificial Ground. Connect one terminal to the radio chassis, the other to whatever wire you have: a baseboard run, a wire out to a balcony, a piece under the desk. Tune the L and C controls until the meter shows a current peak. At that point the wire is resonating, presenting a low impedance, and forcing RF current to flow on it rather than on the chassis and coax.
A 15-foot wire in an L-path along two baseboards can be tuned to look like a proper counterpoise on 40m. Tune per band until the meter peaks. When it does, the current is where it belongs. The MFJ-931 has a built-in current meter that removes the guesswork; the same circuit can be home-built with a PVC-wound series L and a variable capacitor.
What the artificial ground does not do: it does not create an earth connection. It gives RF current a defined path on a controlled wire. That is all it does, and that is all you need it to do.
The Coax Choke: The Other Half of the Fix
Counterpoise solves the "current has nowhere to go" problem. A coax choke solves the "current is using the coax braid as the counterpoise" problem. Both problems are usually present simultaneously.
A 1:1 current choke adds impedance to the outside of the coax shield without affecting the signal inside. With high choke impedance at the feed point, RF current cannot flow down the braid toward the shack. That forces the current to stay on the counterpoise wire instead.
For HF, mix-31 ferrite is correct. Mix-43 rolls off above 30 MHz and is the wrong core for HF common-mode suppression. Mix-31 maintains high impedance across 1-30 MHz. Ten to twelve turns through a large mix-31 core makes an effective choke. Palomar Engineers sells ready-wound chokes and raw mix-31 material. Balun Designs sells purpose-built current chokes for HF, wound correctly and rated for power.
The choke lives at the antenna feed point, not at the radio. That is where common-mode current originates. A choke at the radio end stops current that has already traveled the full length of the coax and gotten into everything else. Choke plus counterpoise together: counterpoise defines the return path, choke locks the boundary. Neither works as well alone.
When You Do Not Need Any of This
Magnetic loops are the exception. A well-designed self-resonant magnetic loop is a complete circuit in itself: current flows around the loop and through the capacitor, the coax couples magnetically rather than connecting directly to the radiating element. No counterpoise requirement, no common-mode current to suppress. If you have no baseboard run and no balcony, the magnetic loop sidesteps the problem entirely. Full treatment in the magnetic loop guide.
What the Fix Actually Gets You
The renter's no-drill HF setup keeps counterpoise brief by design. A few feet of wire off the transformer ground through a choke is the minimum viable fix for 20m and higher. This article is for 40m or 80m operation, severe symptoms, or when you want to understand the mechanism well enough to troubleshoot it yourself.
| Problem | Quick fix | Full fix |
|---|---|---|
| RF on mic/chassis (20m+) | 16-foot counterpoise wire at feed point | Counterpoise + choke at feed point |
| RF on mic/chassis (40m/80m) | MFJ-931 tuning a long baseboard run | Tuned counterpoise to ~33 ft + choke |
| Erratic SWR per band/position | Choke at feed point | Choke + defined counterpoise per band |
| USB/audio dropouts | Ferrite on USB cable + choke at feed point | Choke at feed point + isolated USB hub |
| None of the above working | Magnetic loop (no counterpoise needed) | See magnetic loop guide |
A counterpoise turns a one-wire antenna into a two-wire antenna. It does not turn an indoor wire into a full-size system. What it removes is the self-interference, the RFI into shack equipment, and the erratic SWR that was wasting half your signal. The QRP indoor operating reality article covers the ceiling question in detail.
RF-in-the-shack is not a minor annoyance. It means something else in your shack is acting as the antenna. Defining the return path with a counterpoise and locking the feed point with a choke is fundamental antenna engineering. If you are not sure which antenna path fits your situation, the restricted-space antenna decision tree will route you to the right starting point.
What I Would Actually Put Together
For an end-fed half-wave at a window, fed at the indoor end:
A Balun Designs 1:1 current choke at the transformer output, then a 16-foot counterpoise wire from the transformer ground terminal routed along the baseboard toward the farthest corner of the apartment. If the wire run is longer and you need it to work on 40m, add an MFJ-931 Artificial Ground between the radio chassis and the counterpoise terminal, tuned per band until the current meter peaks. Test by touching the mic body and the chassis. If it is still warm after tuning, try a longer wire or reroute away from the mains wiring in the walls.
For a portable vertical on the balcony:
Two quarter-wave radials from the feed point, zip-tied to the balcony rail and running along the top rail in opposite directions if space allows, or angled down at 45 degrees if the rail is too short. DX Engineering sells radial wire and counterpoise kits in appropriate gauges. A choke at the feed point, same mix-31 material. No artificial ground tuner needed: resonant elevated radials do the job directly.
Either way, the test is simple: key up, check the mic chassis for warmth, watch whether SWR stays stable when you move the coax. If the symptoms are gone, the return path is working. If they are not, the wire is too short, the choke is the wrong mix, or both.