Loaded coil antennas have a narrow bandwidth especially when the shortening ratio is large. I change the element length using pulleys and ropes. The pulleys are set at only one element; it is good enough. As per my 160m inv-vee, the tune frequency can be varied from 1800 kHz to 1916 kHz, covering all the DX band and the JA CW band. The figure shown here is conceptual. I pull and relinquish the ropes at the balcony of the second floor.
短縮アンテナはバンド幅が小さいのをどうやって克服し、広帯域化するか。単純にエレメント帳を可変にすればよい。片方だけでよい。