When selecting an RF cable assembly, antenna feeder, or coaxial jumper cable, the loss chart provides a quick way to compare cable options and evaluate whether the expected attenuation fits the RF link budget. However, actual assembly performance also depends on connector selection, cable construction, impedance matching, routing conditions, and finished product testing.
What a Coaxial Cable Loss Chart Shows
A coaxial cable loss chart normally lists cable attenuation by frequency. The value is often shown as dB per 100 ft, dB per 100 m, dB per meter, or dB per foot. A lower dB value means less signal loss for the same length and frequency.
Most charts are based on the cable itself. They help estimate bulk cable attenuation before connector termination. A finished RF cable assembly has extra variables, including connector interface, crimp or solder quality, adaptor transitions, and impedance mismatch.
Understand the Length Unit
The same chart value can lead to different results if the length unit is read incorrectly. A value listed as dB per 100 ft cannot be treated as dB per 100 m. The cable drawing may use mm, cm, meter, inch, foot, or a custom harness length, so the unit needs to be aligned before comparison.
The basic reading method is simple. Take the attenuation value from the chart, then multiply it by the project length divided by the chart length. If a cable is listed as 6 dB per 100 ft at the target frequency, a 25 ft cable body is about 1.5 dB before connector loss.
For short internal jumper cables, the cable body loss may be small, but connector termination and bending can still affect the finished assembly. For long antenna feeder runs, cable attenuation usually takes a larger share of the loss budget.
Example Loss Chart Reading
The table below is a small reading example, not a full cable selection table. It shows how a dB per 100 m value changes when the same cable is used at 3 m and 10 m. Connector and assembly loss are not included.
| Cable type | Frequency | Chart value | Estimated cable loss at 3 m | Estimated cable loss at 10 m | Reading result |
|---|---|---|---|---|---|
| LMR195 | 900 MHz | 36.4 dB per 100 m | 1.09 dB | 3.64 dB | Usable for short jumper runs, but longer runs need margin review |
| LMR240 | 900 MHz | 24.8 dB per 100 m | 0.74 dB | 2.48 dB | Lower cable loss than LMR195 at the same length |
| LMR400 | 900 MHz | 12.8 dB per 100 m | 0.38 dB | 1.28 dB | Good loss margin, with larger outer diameter to confirm |
| LMR195 | 5800 MHz | 98.1 dB per 100 m | 2.94 dB | 9.81 dB | High frequency use needs short length or another cable option |
| LMR240 | 5800 MHz | 66.8 dB per 100 m | 2.00 dB | 6.68 dB | Better than LMR195, but length is still a major factor |
| LMR400 | 5800 MHz | 35.5 dB per 100 m | 1.07 dB | 3.55 dB | Lower loss, with routing space and connector size to check |
Cable Attenuation and Assembly Insertion Loss Are Different
Cable attenuation is the loss of the cable body. Assembly insertion loss is the measured loss of the finished cable assembly. These two values are related, but they are not the same.
A finished RF cable assembly includes the cable, connector A, connector B, termination area, and any adaptor transition in the link. If the connector is not matched to the cable diameter, shielding structure, or working frequency, the finished result may differ from the cable chart estimate.
This matters for custom RF cable assemblies. The chart can estimate cable body loss, while insertion loss, return loss, and VSWR show how the finished assembly performs at the requested frequency.
Mistakes When Using a Coaxial Cable Loss Chart
One common mistake is reading a low frequency value and applying it to a high frequency project. This can understate the loss by a large margin.
Another mistake is mixing dB per 100 ft with dB per 100 m. The number may look similar, but the length base is different. The estimate becomes wrong as soon as the unit is misread.
A third mistake is treating the chart as the final insertion loss of the cable assembly. The chart does not include all connector and assembly effects. Finished cable assembly testing gives the value that matters for project approval.
A fourth mistake is selecting the lowest loss cable without checking outer diameter and bend space. A cable with better attenuation may still be difficult to route in a compact device or automotive module.
FAQ
Conclusion
A coaxial cable loss chart helps estimate cable body attenuation by frequency and length, but it does not replace finished RF cable assembly testing. For a reliable selection, review the chart value together with connector type, cable length, impedance, routing space, insertion loss, return loss, and VSWR. If your project needs a custom coaxial jumper cable, antenna cable assembly, or low loss coaxial cable with a special length or connector interface, you can share the frequency range, cable drawing, and test requirement with the Bafitop engineering team for review.