Antenna coax must be momentarily shorted before each use, or damage may occur to the MFJ269 Antenna Analyzer.
Simple impedance check: use an accurate SWR meter and divide Zo, 50 ohms, by the SWR. Do not use this method unless Xs reactance is very close to 0 ohms, if antenna Z is greater than Zo, or if SWR is very high. Antenna load should be resistive only. For more information about formulas used in the calculations below, see: Radio Electronics Formulas
Run each test several times. Tests can be inaccurate due to nearby metal structures or elements, as well as other conditions, including strength of the mag
mount, earth ground, etc.
½ Wave Length Inverted VEE – Apex angle 90º
| Resonance Freq. (MHz) | Rs (ohms) | Xs (ohms) | SWR | Zo / SWR (ohms) | Z measured (ohms) | Z calculated (ohms) |
|---|---|---|---|---|---|---|
| 14.380 | 27 | 9 | 1.9 | 26 | 26 | 28.46 |
¼ Wave Length – 50” With Center Load Coil and Mag Mount on Car Roof
| Resonance Freq. (MHz) | Rs (ohms) | Xs (ohms) | SWR | Zo / SWR (ohms) | Z measured (ohms) | Z calculated (ohms) |
|---|---|---|---|---|---|---|
| 14.148 | 41 | 20 | 1.6 | 31.25 | 45 | 45.617 |
Note: High Xs reactance leads to poor impedance estimation via the simple impedance check.
½ Wave Roll-up J 300 ohm Twin Lead – 72” coax length
| Resonance Freq. (MHz) | Rs (ohms) | Xs (ohms) | SWR | Zo / SWR (ohms) | Z measured (ohms) | Z calculated (ohms) |
|---|---|---|---|---|---|---|
| 146.73 | 45 | 3 | 1.1 | 45.45 | 45 | 45 |
¼ Wave 19” Mag Mount on Car Roof
| Resonance Freq. (MHz) | Rs (ohms) | Xs (ohms) | SWR | Zo / SWR (ohms) | Z measured (ohms) | Z calculated (ohms) |
|---|---|---|---|---|---|---|
| 146.45 | 41 | 8 | 1.2 | 41.66 | 40 | 41.77 |
FM Dipole 50” Display Antenna (468 ÷ 103.97 = 4.5 ft. x 12 = 54”)
| Resonance Freq. (MHz) | Rs (ohms) | Xs (ohms) | SWR | Zo / SWR (ohms) | Z measured (ohms) | Z calculated (ohms) |
|---|---|---|---|---|---|---|
| 103.97 | 52 | 1 | 1 | 50 | 50 | 52 |
Prepared by Gary Davis, KD9SB, 07-11-18
References
- MFJ269 Antenna Analyzer: www.mfjenterprises.com
- Radio Electronics Formulas