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| To: | [email protected] |
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| Subject: | LF: Harmonics |
| From: | Richard Rogers <[email protected]> |
| Date: | Tue, 04 Feb 2014 08:43:12 +1100 |
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G'day,When Robert, AX2TAR, was experimenting here on 178KHz, I built a 100W class D transmitter for him to try. He thought the five element low pass filter on the output was redundant as the antenna loading coil should provide sufficient selectivity. So he tried it one night without the filter, feeding the square waves via his LF loading coil to the antenna. I could barely hear his 3rd and 5th harmonics, but the 17th, 19th, 21st and 23rd harmonics were loud and clear. The strongest was about S8. Robert lived about 15KM away from me. I think this was because his antenna wire was about a halfwave long near these frequencies and thus had a high input impedance which was efficiently coupled to the transmitter by the stray capacitance across the LF loading coil. Perhaps some of the current VVLF experimenters would like to try listening for higher harmonics than the third. -- 73, Ric VK7RO |
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