Comparing signal attenuation at 1420 MHz in short 30cm jumper coaxial cables RG174 vs RG316
For a 30 cm jumper at 1420 MHz (H I line), RG174 and RG316 are effectively neck-and-neck—both cost you ~⅓–½ dB pre-LNA.
Quick comparison (30 cm @ ~1.5 GHz)
- RG174: spec examples put loss ≈ 1.5 dB/m @ 1.5 GHz → ~0.45 dB for 0.3 m. (Reichelt)
- RG316: published figures vary by maker; typical ~1.0–1.55 dB/m @ 1.5 GHz → ~0.33–0.47 dB for 0.3 m. (TME)
That translates to an added receiver noise temperature of roughly +23–33 K for either cable over 30 cm (pre-LNA).
Other parameters that might matter at the feed
- Velocity factor: RG174 ≈ 0.66; RG316 ≈ 0.69 (slightly shorter electrical length for RG174). (Mouser Electronics)
- Temp rating: RG174 typically –25 °C…+85 °C (PVC); RG316 –65 °C…+200 °C (PTFE/FEP). (Mouser Electronics)
- Shielding (single braid): RG174 ≥40 dB up to 1 GHz; RG316 ≥38 dB up to 1 GHz. Double-braid (e.g., RG316D) jumps to ~70–80 dB and is preferable at L-band. (Mouser Electronics)
- Bend radius (static): both about 15 mm. (Mouser Electronics)
Bottom line
- For a short, 30 cm pre-LNA pigtail, pick RG316 for its high temperature rating, PTFE dielectric, and generally better build/connectors. Loss vs RG174 is within ~0.1 dB at this length—basically a wash.
- If you need better shielding at the feed, use RG316D (double-braid) or semi-rigid; if you want lower loss in a small form factor, LMR-100A is a drop-in with meaningfully less loss than either RG174/316 for longer runs (but still keep anything pre-LNA as short as physically possible). (hubersuhner.com)
If you want, I can plug in your exact pigtail length and connector count to estimate total insertion loss and added noise temp for your specific feed layout.