One of the most critical factors affecting receiver performance when using the HackRF One and a low-noise amplifier (LNA) is the signal loss incurred in the coaxial cable connecting the antenna to the receiver. Coaxial cables, especially at higher frequencies, can introduce significant attenuation (loss), which reduces the amplitude of the received signal before it even reaches the LNA or the SDR. For example, common RG-58 cable can lose several dB per 10 meters at VHF and UHF frequencies. This loss not only attenuates the signal but also elevates the effective noise floor at the receiver end, as the weak signals become harder to distinguish from noise. If the LNA is placed at the antenna, it amplifies the signal before any significant loss occurs, preserving the signal-to-noise ratio (SNR). Conversely, if the LNA and SDR are located far from the antenna and connected via a long coaxial cable, the weak RF signals are attenuated before amplification, leading to a lower SNR and degraded performance. Therefore, minimizing cable length between antenna and LNA is crucial for optimal sensitivity, especially for weak signals and higher frequencies.
The noise figure (NF) of a receiver system is a key metric that determines how much noise the system adds to the received signal. Placing the LNA directly at the antenna ensures that the first active component in the signal chain has a low noise figure, which dominates the overall system noise performance (as described by Friis' formula). This is especially important for software-defined radios like the HackRF One, which have moderate noise figures and front-end sensitivity. If the LNA is located near the SDR, after a long coaxial run, the losses in the cable degrade the overall noise figure, because the cable's loss and noise are added before amplification. This results in a system that is less capable of receiving weak signals. By mounting the LNA at the antenna, the weak signal is immediately amplified, and the impact of subsequent cable losses and the SDR's own noise figure is minimized. This setup is widely recommended in recent amateur radio, satellite, and radio astronomy applications using SDRs, as it yields significantly better reception quality, particularly in low-signal environments.
The HackRF One is a versatile SDR platform, but it lacks a high-performance front-end preamplifier and is susceptible to reduced sensitivity when dealing with weak signals, especially at higher frequencies. Recent user reports and technical discussions (2023-2024) emphasize that for best results, an external LNA should be installed as close to the antenna as possible. This approach not only counters the inherent noise figure limitations of the HackRF One but also mitigates losses from any necessary coaxial runs. However, practical issues such as powering the LNA (using bias tee or external power), weatherproofing, and physical security must be considered. In some cases, if only strong local signals are of interest, or cable runs are very short (a meter or two), placing the LNA and SDR together may be acceptable. But for most scenarios—especially satellite reception, weak signal DXing, or wideband scanning—the consensus is clear: mounting the LNA at the antenna provides a substantial improvement in SNR and system sensitivity. This setup has become standard best practice for HackRF One users seeking optimal receiver performance.