Here are typical signal attenuation figures (loss) for common coaxial cables at around 1.42 GHz (1420 MHz) — expressed as dB per unit length. Coax loss increases with frequency, so, for example, you’ll see higher losses at UHF compared with VHF, and even higher losses at microwave frequencies (or 1420 MHz).
Cheaper cables, such as RG-6, can be used as long as there is filtering and amplification at the masthead (just behind the waveguide) using a low power amplifier and filter such as the Nooelec SAWBird H1+ LNA. However, this MUST be positioned close to the waveguide and not at the other end of the coaxial cable near the software defined radio (SDR).
📡 Approximate Attenuation at ~1.4 GHz (1420 MHz)
| Cable Type | Approx. Loss | Units & Notes |
| RG-58 (50 Ω) | ~21 dB per 100 ft (~69 dB/100 m) | Very high loss at 1.4 GHz — not ideal for long runs; figures from measured tables scaled to ~1.2–1.5 GHz. |
| RG-6 (75 Ω) | ~15–20 dB per 100 ft (~45–60 dB/100 m) | RG-6 is 75 Ω and not impedance-matched for 50 Ω systems, but gives a rough loss reference. |
| LMR-240 (50 Ω) | ~12–13 dB per 100 ft (~35–40 dB/100 m) | Typical loss from manufacturer specs and published attenuation charts. |
| LMR-400 (50 Ω) | ~4.8–6.8 dB per 100 ft (~15–22 dB/100 m) | Much lower loss than small-diameter coax; typical value at ~1.2 GHz extrapolated to ~1.4 GHz. |
📏 Per-Metre Rough Conversion (approx)
If you prefer dB per metre (useful for short or long runs):
| Cable Type | ~1.42 GHz Loss | dB/m (approx) |
| RG-58 | ~69 dB/100 m | ~0.69 dB/m |
| RG-6 | ~50 dB/100 m | ~0.50 dB/m |
| LMR-240 | ~38 dB/100 m | ~0.38 dB/m |
| LMR-400 | ~18 dB/100 m | ~0.18 dB/m |
Notes:
• These are typical values based on manufacturer specs and published coax loss charts; actual loss depends on brand, dielectric type, temperature and manufacturing tolerances.
• RG-6 is 75 Ω cable and therefore not ideally matched to most 50 Ω radio systems — using it will also introduce mismatch loss in addition to attenuation. However, for systems that only receive and do not transmit this is less of an issue.
• Loss increases roughly with frequency — these figures are interpolated/extrapolated around 1 GHz to 1.5 GHz ranges for common cable types.
📊 Practical Summary for comparison of RG-58, RG-6, LMR-240, and LMR-400 coaxial cables
- RG-58: Poor choice for ~1.42 GHz unless cable run is very short — loss is very high.
- RG-6: Better than RG-58 but still high loss and impedance mismatch for 50 Ω systems.
- LMR-240: Mid-range performance—moderate loss for medium-length runs.
- LMR-400: Best of the listed options for low loss at ~1.4 GHz, suitable for long runs if you need low attenuation.
📊 Extending the analysis to wider range of coaxial cables
Here’s a comparative table of typical attenuation (loss) around ~1.42 GHz (1420 MHz) for a wider set of common coaxial cables — mostly expressed as dB loss per 100 m (you can easily convert to dB/100 ft by dividing roughly by 3.3). These figures are drawn from published attenuation charts and manufacturer data. Actual loss varies with exact make/model, temperature, and installation, but this gives a practical engineering reference.
| Cable Type | Approx Attenuation @ ~1.4 GHz | dB/100 m (≈) | Notes |
| RG-58 | ~69 | Very high loss UHF cable; only OK for very short runs. | Avoid this cable |
| RG-8X | ~53 | Lower loss than RG-58 but still significant at 1.4 GHz. | |
| RG-213/214 | ~33 | Good general-purpose low-loss 50 Ω cable. | |
| LMR-195 | ~48 | Lower loss than RG-58 but still fairly high at UHF. | |
| LMR-200 | ~20 | Moderate loss; better than smaller RG but not great for long runs. | |
| LMR-240 | ~30 | Mid-range low-loss coax. | Good general choice |
| LMR-400 | ~16 | Very popular low-loss 50 Ω cable; good for many runs. | Excellent choice, increased cost |
| LMR-400-DB (direct burial) | ~17 | Slightly higher due to rugged outdoor design. | |
| LMR-500 | ~27 | Larger than 400, but higher loss than LMR-400 at UHF. | |
| LMR-600 | ~10 | Low loss bigger coax, excellent choice for longer runs. | For those with deep pockets (lots of money) |
| Belden 9913 | ~17 | Another low-loss 50 Ω option. | |
| 3/8″ LDF (Heliax) | ~14 | Heliax rigid coax; good for quite long high-frequency runs. | Rigid coaxial cable is not generally recommended for amateur radio telescope systems, unless there is a specific indication. |
| 1/2″ LDF (Heliax) | ~9 | Larger Heliax with low loss. | |
| 7/8″ LDF (Heliax) | ~5 | Very low loss for UHF & microwave. | |
| 1¼″ LDF (Heliax) | ~4 | Excellent low loss for long runs at GHz. | |
| 1⅝″ LDF (Heliax) | ~3 | Extremely low loss; heavy and expensive. |
📌 Quick Practical Notes
- Small jumper coax (e.g., RG-58, RG-8X) suffers very high loss at 1.42 GHz — suitable only for very short connections or low-power receive applications.
- Mid-size low-loss cables like LMR-240 / LMR-400 / 9913 are popular for UHF use and balance performance and flexibility.
- Larger “Heliax” type coax (½″ and up) offers much lower attenuation per length and is ideal for long runs, but is heavier and more expensive.
- LMR-600 sits between flexible coax and large Heliax, giving low attenuation with reasonable flexibility.
📏 Conversions & Rough Per-Metre Figures
To convert to dB per metre roughly: divide the dB/100 m value by 100. For example:
- LMR-400: ~0.16 dB/m at ~1.4 GHz.
- 7/8″ Heliax: ~0.05 dB/m.
- RG-58: ~0.69 dB/m.