RF Feedline (Coax and Ladder-Line) Loss and ERP Calculators
This program is provided “AS-IS.” It is the responsibility of the user to verify the accuracy of the calculations when using this program. Always look up the cable manufacturers’ specifications and installation guides for any RF cable prior to purchase and use.
Please don’t ask me to add another coax! I don’t know where or how the K1 and K2 constants used in the arrays were obtained or derived.
Coax and Ladder-Line Info
Basic Feedline Facts for Hams
- RG-174 (50 ohms) is very small (~0.11") and lossy. Suitable only for short pigtails and jumpers at very low power, as in receivers, scanners, etc.
- RG-58 (50 ohm) is about 0.195", quite lossy, suitable only for mobile installations (typically < 20 feet, < 150 watts).
- RG-6 (75 ohms) is about 0.332", typically used for cable/satellite TV.
- RG-8X (50 ohm); and and RG-59 (75 ohm) are about 0.24 inch. Suitable for medium power (~350 watts), HF and Lo-VHF.
- RG-8 and RG-213 (50 ohm); and RG-11 (75 ohm) are about 0.405 inch. Suitable for higher power (~1800 watts) at HF.
- 9913 and LMR-400 are popular “low-loss” RG-8 types. Suitable for VHF (~1.5dB loss per 100 feet at 146 MHz). The flexible types (9913F and LMR-400UF) are preferred, particularly for rotatable antennas. However, stranded center conductors have a little higher loss than solid ones.
- There are at least four commonly-used types of coax dielectric: (1) semi-solid polyethylene (PE) for temps up to 80°C (Vp 66%); (2) gas-injected PE (foam PE) for temps up to 100°C (Vp ~85%); (3) air-core: a thinner PE with a PE strand spiraled around the inner conductor (Vp ~85%); and (4) PTFE (Teflon) for temps up to 250°C.
- All foam-type coax cables should be taped—not attached with plastic cable ties or wire—to tower legs, etc., to prevent deforming of the foam dielectric.
- Windowed ladder-line (WLL) should be (1) kept at least a few inches from metal (to prevent magnetic induction losses); (2) twisted 1/2 turn per foot (to prevent wind flap); and (3) turned at a large radius (12 inches or more). It has a VF of 91-95%. See also KV5R’s Ladder-Line pages.
- Though frequently ignored, all RF transmission lines have maximum RMS voltage, and maximum power (wattage), which varies with type, brand, and frequency.
- How much attenuation is acceptable? Well, a mere 3dB will waste 50% of your wattage!
Coax and Ladder-Line Data
Click the links below for manufacturers’ data-sheets.
Note: the RG numbers given are not actual labels, but are given merely for familiarity.
9913 RG-8A (low-loss)
Times Microwave (Times Calculator):
Wireman (coax data table - docx):
Heliax LDF4-50A 1/2 in.
Heliax LDF5-50A 7/8 in.(obsolete)
Heliax LDF6-50 1-1/4 in. (obsolete)
Wireman (1" WLL):
551 (#18 solid)
552 (#16 stranded)
553 (#18 stranded)
554 (#14 stranded)
Generic 300 ohm Tubular
Generic 450 ohm Window
Generic 600 ohm Open
Ideal (lossless) 50 ohm
Ideal (lossless) 75 ohm
*"Wet" numbers are worst case
for lines with ice or snow.
Line Loss Calculator:
Note: Set Line Length 100 here to use the ERP Calc. Put actual line length in the ERP Calc.
Effective Radiated Power Calculator:
Transmission Line Loss technical tutorial from microwaves101.com
Online Calculator from Times Microwave