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| To: | <[email protected]> |
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| Subject: | LF: Re: Antenna Matching |
| From: | "James Moritz" <[email protected]> |
| Date: | Sun, 28 Mar 2010 12:14:18 +0100 |
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Dear Tim, LF Group,Since your T is much less than a quarter wave long, you will need series inductance (a few hundred uH) to resonate it at 500k. The antenna will have a capacitive reactance of the order of 1kohm, and series loss resistance probably between several ohms and a few 10s of ohms. With 100W, this will result in no more than about 5A antenna current, so about 5kV maximum on the antenna, not very high voltage as these things go. The two most common methods of matching a 500k antenna are to use a series loading coil to resonate the antenna, and a multi-tapped ferrite cored transformer to transform the resulting resistance to 50R, or a tapped loading coil with the "cold" end grounded, and the tapping point a few turns from the grounded end connected to the transmitter adjusted to match to the TX. In both cases, the loading coil usually has several taps to make coarse inductance adjustments, with usually a variometer for fine tuning to resonance. It is possible instead to use a high voltage tuning capacitor for fine adjustment of resonance, but this will generally increase losses in the coil. Good luck on 500k, Cheers, Jim Moritz73 de M0BMU |
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