13 Mar 2014

Very Low Marconi on 472kHz

As from mid-afternoon I am now using a very low height Marconi on 472kHz, tuned against the mains earth (that attaches to a decent ground). The average top horizontal section height is about 1.8m with a horizontal length - a wire along the top of a fence and trellis in an L-shape with a length of around 30m. The whole antenna is just about invisible. The vertical section is just the wire up to the top of the  fence.

The whole antenna resonates with a 108uH inductance in series (wound on 110m diam. former) and this is matched to the 12W RF out transverter with a 42mm diameter 3C90 tapped toroid. The antenna looks like 300-400 ohms and the antenna current is 0.64A measured with my current meter. I have ESTIMATED ERP as around 10mW but am probably in a position to calculate this now.

Performance of the very low Marconi compared with the 15m earth-electrode antenna, is about 6-7dB better over probable ground wave paths. So far, the only skywave signal suggests a less noticeable improvement, I think.

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