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) is not always a good receiving (RX) antenna. Here’s why:

1. High Rr and TX Efficiency

A high radiation resistance generally improves TX efficiency, as more of the applied RF power is radiated rather than lost as heat in the antenna structure or ground losses.

However, high Rr does not automatically mean the antenna has a good signal-to-noise ratio (SNR) when receiving.

2. RX Performance is Dominated by Noise and Impedance Matching

RX antennas should maximize the signal-to-noise ratio (SNR), not just capture strong signals.

An ideal RX antenna should have a low noise floor and be well-matched to the receiver’s front-end impedance.

Many efficient TX antennas also pick up a lot of local noise (e.g., man-made noise, QRM, QRN), making them poor RX antennas in noisy environments.

3. Reciprocity vs. Practical Factors

Antenna reciprocity states that an efficient TX antenna should also be efficient for RX.

However, the key difference is that:

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

• RX performance depends on reducing noise pickup and optimizing received signal strength.

4. Noise Performance and RX Antenna Choice

For receiving, often small active antennas (like our highly optimized  E-probes (EchoTracer) and Active MagLoops (OctaLoop)) perform better in noisy environments because they have a high signal-to-noise ratio (SNR) and are less affected by local noise.

Large TX antennas, especially those low to the ground, can act as excellent noise collectors rather than good RX antennas.

5. Examples of TX vs. RX Antennas

Good TX but Poor RX: A full-size 160m dipole close to the ground (strong TX, but high noise on RX).

Good RX but Poor TX: A short E-probe (like our EchoTracer) or a magnetic loop (like our OctaLoop), which can have a great SNR but not suitable for TX at all.

Conclusion

A TX antenna with high Rr is not always a good RX antenna, especially in noisy environments. Low-noise, high-SNR antennas (like E-probes, loops, and beverages) are often better suited for RX, even if they are inefficient for TX.

Article written by Joeri Van Dooren, ON6URE – RF engineer, antenna designer, and founder of RF.Guru. With extensive experience in active and passive antenna systems, high-power RF transformers, and custom RF solutions, Joeri shares insights into cutting-edge radio communication technologies.