When sourcing coaxial cable for RF (radio frequency) applications, one of the most critical technical parameters is attenuation—the loss of signal strength as it travels along the cable. Attenuation is typically expressed in dB per 100 meters (dB/100m) and varies significantly with frequency. Understanding this relationship is essential for selecting the right cable for your system, whether for telecommunications, broadcasting, CCTV, or data networking. This article explains the fundamentals of coaxial cable attenuation at different frequencies and provides guidance on how to interpret supplier specifications for informed sourcing decisions.

Attenuation in coaxial cables arises from two primary sources: conductor resistance and dielectric losses. At low frequencies (e.g., below 1 MHz), conductor resistance dominates, and the loss is relatively low. As frequency increases, the skin effect forces current to flow near the surface of the conductor, effectively increasing resistance and thus attenuation. Simultaneously, dielectric losses—caused by the insulating material between the center conductor and shield—become more significant at higher frequencies. The result is a nonlinear increase in attenuation per 100m as frequency rises.

For practical sourcing, you will encounter attenuation data at key frequency points. For example, a typical RG58 cable (50 ohm) may have an attenuation of about 6.6 dB/100m at 10 MHz, 13.5 dB/100m at 100 MHz, and 32.8 dB/100m at 400 MHz. In contrast, a higher-grade cable like LMR-400 shows much lower loss: approximately 1.5 dB/100m at 10 MHz, 5.4 dB/100m at 100 MHz, and 11.3 dB/100m at 400 MHz. These differences stem from cable construction—larger center conductors, low-loss foam dielectrics, and better shielding reduce attenuation. When sourcing, always check the specified frequency range of your application. For instance, cellular systems operating at 700–2700 MHz require cables with low loss at high frequencies, while baseband video (0–10 MHz) can tolerate higher loss per 100m.

The table below illustrates typical attenuation values for common coaxial types at three standard frequencies:

- RG59 (75 ohm, solid dielectric): 10 MHz: 5.2 dB/100m; 100 MHz: 14.8 dB/100m; 1000 MHz: 42 dB/100m

- RG6 (75 ohm, foam dielectric): 10 MHz: 3.3 dB/100m; 100 MHz: 8.2 dB/100m; 1000 MHz: 25 dB/100m

- LMR-600 (50 ohm, low-loss foam): 10 MHz: 0.8 dB/100m; 100 MHz: 3.1 dB/100m; 1000 MHz: 9.8 dB/100m

These numbers highlight a key sourcing principle: while higher-quality cables reduce loss, they also cost more and may have larger diameters and reduced flexibility. Therefore, you must balance performance against budget and physical constraints. For long runs (e.g., 100m or more), attenuation accumulates linearly—if a cable loses 10 dB/100m, a 200m run loses 20 dB, which can significantly degrade signal-to-noise ratio. Amplifiers may be required, but they introduce their own distortion. Always request a datasheet from your supplier that provides attenuation values at multiple frequency points, preferably in graph or tabular form, covering the full operational range of your device.

Another factor to consider is the impedance (typically 50 or 75 ohms). Mismatch between cable and equipment impedance causes additional power loss and reflections. For example, 50 ohm cables are standard for radio transmitters, antennas, and test equipment, while 75 ohm cables are common in video and cable TV systems. Attenuation per 100m is usually specified for matched loads; any mismatch increases effective loss.

When sourcing, also note the test frequency for attenuation data. Some suppliers specify loss at 1 GHz or 2.4 GHz, but your system may operate at lower frequencies. Using a cable with excellent high-frequency performance at a low frequency is acceptable, but the reverse (using a cable designed for low frequency at high frequency) can lead to severe signal loss. For instance, using standard RG59 at 2.4 GHz could yield attenuation exceeding 60 dB/100m, making it unusable for Wi-Fi or Bluetooth links.

In summary, sourcing coaxial cable requires careful evaluation of attenuation per 100m at the specific frequencies you intend to use. Always cross-reference vendor data with your system requirements. For short runs (under 10m), lower-grade cables may suffice; for long or high-frequency links, invest in low-loss cables like LMR or Belden types. Use the attenuation table or graph to calculate total system loss, and leave a 3–5 dB margin for connector losses and aging. Remember that lower attenuation directly translates to stronger signals, better transmission distances, and reduced error rates. By mastering this parameter, you can make cost-effective, performance-optimized decisions when sourcing coaxial cable.