All posts by KC9YUA
2022 HAMFEST
Decibels
From a presentation on decibels by Gary Davis, KD9SB: what they mean and how to compute them.
Wireless Morse Code Practice Circuit
Practice Circuit with Morse Key, AM Radio, and Power Source
Note: the FCC allows low-power, unlicensed transmission (effective service range < 200 ft without interference) in the AM and FM bands. See: Part 15 Devices. Check your local jurisdiction before transmitting.
MFJ269 Antenna Analyzer Test Results
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
Storm Spotter Resources
- Comet Online Skywarn Course
- National Weather Service on Facebook
- NWS Indianapolis on Facebook
- NWS Indianapolis Severe Weather Page
- NWS Indianapolis Spotter Page
- NWS Jetstream Online Weather School
- NWS Office of Services, Publications, and Brochures
- NWS Storm Spotter Training Portal
- NWS Dual Polarization Radar Training
- NWS Weather Ready Nation Site
- NWS Weather Ready Safety Page
- SPC Mesoscale Analysis Parameter Explanations
- Storm Prediction Center
- University of Illinois Weather World 2010 Project – Meteorology Education
- Weather Spotter’s Field Guide
- Become A Storm Spotter From Home