Is a TX antenna (with high radiation resistance) always a good RX antenna?

Not necessarily. A transmitting (TX) antenna with a high radiation resistance (Rr) can be very efficient on transmit, but that does not automatically make it the best receiving (RX) antenna for your noise environment. Here’s why:

High Rr and TX Efficiency

In simple terms, radiation resistance (Rr) is the “equivalent resistance” at the feedpoint that represents power converted into electromagnetic radiation.

For a given amount of loss resistance (conductor loss, loading components, ground system losses, etc.), a higher Rr usually means higher TX efficiency, because a smaller fraction of the applied RF power is dissipated as heat.

But what matters is the ratio between Rr and the total loss resistance (Rr / (Rr + Rloss)), not Rr by itself.

And even excellent TX efficiency does not automatically imply a better signal-to-noise ratio (SNR) on receive.

RX Performance is Dominated by Noise, Pattern, and System Matching

On RX, the goal is to maximize the SNR (or intelligibility) at the receiver input, not just “make the S‑meter go up.”

If your band/location is dominated by external noise (typical on HF: QRN/QRM), a bigger or more efficient antenna often increases signal and noise together, so SNR may not improve.

In quieter environments (often VHF/UHF, remote sites, or very low-noise receiving setups), antenna efficiency/gain and a low-noise, high-linearity front end can make a real difference because receiver noise can be the limiting factor.

Impedance matching still matters: it helps transfer available signal power, maintain expected noise performance, and avoid overload or bandwidth issues. But a perfect conjugate match is rarely required for good reception, and the “best” match can depend on the receiver design.

Reciprocity vs. Practical Factors

Antenna reciprocity (for passive, linear antennas) means the antenna has the same radiation pattern, polarization, and gain on transmit and receive. So a high-efficiency TX antenna is generally also a high-gain RX antenna — in the same directions and polarization.

What reciprocity does not guarantee is the best SNR at a specific site, because that depends on the noise field around the antenna and how the receive system is installed (common-mode currents, feedline coupling, nearby electronics, etc.).

Also note: active receive antennas (with amplifiers) introduce their own noise and linearity limits, so the overall RX performance can differ from what the passive antenna alone would suggest.

• TX efficiency focuses on minimizing losses and maximizing radiated power.

• RX performance depends on maximizing SNR via pattern/polarization/placement and controlling noise coupling.

Noise Performance and RX Antenna Choice

In many real stations, the best receive antenna is the one that rejects local noise best — even if it would be inefficient or impractical for high-power TX.

Examples include directional receive antennas (Beverage, flag/pennant), and small magnetic loops that can be less sensitive to local electric-field noise sources.

Small active antennas (such as receive-optimized E-field probes (EchoTracer) and active magnetic loops (OctaLoop)) can also work very well when they have adequate filtering and dynamic range — but their amplifier noise and overload behavior become part of the RX system performance.

A large, efficient TX antenna installed close to buildings, wiring, or electronics can couple strongly to man-made noise through the feedline or near field. Sometimes the biggest RX improvement comes from moving the antenna, improving common-mode suppression (chokes/baluns), or using a separate RX antenna located farther from noise sources.

Examples of TX vs. RX Antennas

Good TX but Noisy RX (site-dependent): A full-size HF dipole or vertical that transmits well, but is installed near household RFI sources (switch-mode supplies, solar inverters, LED drivers, etc.) can show excellent SWR/efficiency yet deliver a high noise level on receive.

Good RX but Poor TX: A terminated Beverage/flag, a small E-field probe (like our EchoTracer), or an active magnetic loop (like our OctaLoop) can provide excellent SNR and wideband coverage, but these are generally intended for receive only (limited power handling). Note: a resonant passive “small transmitting loop” is a different design and can be used for TX.

Conclusion

A TX antenna with a high radiation resistance can be an excellent antenna in terms of efficiency and gain — and by reciprocity it will also receive well in the same directions and polarization. But it is not automatically the best RX antenna when local noise dominates. For RX, prioritize high SNR: placement away from noise sources, pattern/polarization that rejects interference, common-mode control, and a clean front end. In many stations, a dedicated receive antenna (loops, beverages, flags, E-probes) can outperform the main TX antenna in intelligibility, even if it would be inefficient for TX.

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Written by Joeri Van Dooren, ON6URE – RF, electronics, and software engineer; complex platform and antenna designer. Founder of RF.Guru. Experienced in active and passive antennas, high-power RF transformers, and custom RF solutions, with a background in telecom and broadcast hardware (set-top boxes, transcoders, and E1/T1 switchboards). His work spans high-power RF, embedded systems, digital signal processing, and complex software platforms in both amateur and professional communications.