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307 (307)
| | Posted on Tuesday, June 12, 2001 - 7:18 pm: | 
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If you are an amplifier user , pull a 4 foot florescent lamp down out of the wifes kitchen. Take it out to your car , turn on the CB and Linear , Have her key it up while you hold the florescent lamp near the antenna (about 2" to start)it will light up like the sun. Then see how far you can walk away and it still stays lit. I have seen it 20' away. You can use a small 6" florescent bulb that you can get at the hardware store to see exactly WHERE your antenna is radiating the most power. Is it the TOP? or BOTTOM? I would like to hear your results. |
HAM CBer
| | Posted on Friday, June 15, 2001 - 1:15 pm: |
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307, good experiment that is always a thrill to see!
KEEP IN MIND: The fluorescent bulb thing will only show where the high voltage/low amperage nodes of your antenna element are, but that does not show 'WHERE your antenna is radiating the most power' unless you use it to walk around your car as a field strength meter. Even that is not entirely accurate. A diode detector works better since it shows the actual RF radiated and not just the high voltage.
Antenna elements have different current and voltage nodes all along their length. Fluorescent bulbs respond to high voltage and require little to no amps to illuminate the phosphorescence inside.
If you run 1KW into a 1/4 wave antenna with a 50 ohm, j0 load, you will see (+/-) 4 amps at the feed point with somewhat low voltage. If you base feed a 1/2 wave length antenna element, after the matching transformer at the actual feed point, you will see a load more like 500 ohms, -j35. The amperage would be in the milliamp range and the voltage would be very high.
Sorry for the mumbo-jumbo. I tried to simplify this as much as possible. Amongst other things I do for a living, is professional antenna systems. I cheated. |
bullet/151 southern Indiana
| | Posted on Saturday, June 16, 2001 - 5:04 am: |
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ham cber tell me more about the diode detector please.thanx bullet |
HAM CBer
| | Posted on Sunday, June 17, 2001 - 3:51 am: |
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A diode detector is the same thing as a passive (non-amplified) field strength meter. In its simplest form, it is made up of a sensitive meter movement with a germanium small signal diode across it. The anode terminal of the diode connects to the + terminal of the meter along with an antenna and the other side connects to ground. |
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