Most spec sheets list attenuation "per 100 m at 900 MHz / 2 GHz" — but in the field you start from the opposite end: "my link can tolerate at most X dB loss over Y meters at this frequency, what cable do I need?" Here is the reverse-engineering method our application engineers use.
Start from system requirements, not from a catalogue:
Required attenuation per 100 m = (Max allowable loss ÷ L) × 100. This single number drives the whole selection.
Lower required dB/100m ⇒ larger, lower-loss cable. Typical 50Ω feeder reference values (≈ values at 900 MHz):
| Cable | Type | Atten. ≈ dB/100m @900MHz | Use when |
|---|---|---|---|
| PTL240 / LMR240 | Braided | ~12–14 | Short indoor/DAS jumps |
| PTL400 / LMR400 | Braided | ~6.5–7.5 | Medium runs, flexible routing |
| 1/2″ corrugated | Cu/Al tube | ~4.5–5.5 | Building-to-antenna feeders |
| 7/8″ corrugated | Cu/Al tube | ~2.8–3.2 | Macro base-station trunks |
| 1-5/8″ corrugated | Cu/Al tube | ~1.6–1.9 | Long high-power runs |
Pick the smallest cable whose attenuation ≤ your Step-1 number, then verify at your actual frequency (use the full datasheet curves, not just the 900 MHz point).
Requirement: 60 m feeder at 2.1 GHz, max 3.0 dB loss; flexible routing preferred.
Step 1: 3.0 ÷ 60 × 100 = 5.0 dB/100m at 2.1 GHz.
Step 2: At 2.1 GHz, 1/2″ corrugated ≈ 8–9 dB/100m (too high); PTL400 braided ≈ 11 dB/100m (too high); 7/8″ corrugated ≈ 5 dB/100m — meets it. If routing flexibility is critical and runs shorter, PTL600 braided may also qualify.
Step 3: Choose 7/8″ corrugated copper-tube feeder with 7/16 DIN connectors, +1 dB margin → validated.
Send us frequency, length and allowable loss and we'll return a recommended model with the measured attenuation curve.