Frequency: 144 MHz Return Loss: -12 dB VSWR: 1.8:1 Gain: 3.2 dBi
To build an effective J-pole, dimensions must be precise based on your target frequency. The standard formula uses the speed of light adjusted for the velocity factor of the material (typically copper pipe or 300-ohm twin-lead). Standard Formulas (in inches) 8856 / Frequency (MHz) Radiator Length: 5540 / Frequency (MHz) Stub Length: 2770 / Frequency (MHz) Spacing: ~2 inches for VHF; ~1 inch for UHF 2-Meter Band Example (146 MHz) Overall Length: 60.6 inches Radiator: 37.9 inches Stub: 19.0 inches Construction Steps j-pole antenna design pdf
| Problem | Likely Cause | Fix | |---------|--------------|-----| | High SWR across band | Stub length wrong | Adjust shorting strap | | Narrow bandwidth | Too thin conductor | Use larger diameter tubing | | RF in shack | Missing choke | Add ferrite balun | Frequency: 144 MHz Return Loss: -12 dB VSWR: 1
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