G7FEK Limited Space Antenna Suomen （芬兰G7FEK有限的空间天线）.pdfVIP

G7FEK Limited Space Antenna G7FEK Multi-band “Nested Marconi” Antenna - 2008 Version (rev 5) A 46 ft multi band antenna for small gardens that works well on 80 meters Main bands (@~50 ohm) are 80m / 40m / 30m / 17m / 15m / 12m Other bands (see text): 20m / 10m 38 ft (11.7m) 8 ft (2.5m) 24 ft (7.4m) 50 Ohm Coaxial This antenna was first conceived as a simple dual band antenna in 1988, in an attempt to achieve sensible dual band operation in a small garden of 14m (46 ft) length. Evolving from a simple end-fed Marconi for 80m, the idea was to use the opposing harmonic relationships of two ¼ wave elements so that they could be fed on odd harmonics without mutual coupling. This principle has been used with nested dipole antennas and other specialist multi-band antennas such as the Cobweb, but because of interaction and coupling issues, it’s rarely implemented on end fed wire antennas. With this version of the antenna, interaction between elements and top resonance have been turned to our advantage allowing for excellent multi-band working, while maintaining a useful radiation pattern and efficiency on almost all Amateur Radio bands. The suggested dimensions provide for low radiation angle (30 to 40 degrees) on all bands except 30m where the antenna acts as a full size horizontal dipole. Low VSWR is achievable on most bands and, with careful construction, up to four bands can be used without ATU. Radiation resistance is in the range 25 to 200 ohms on all bands, ensuring high radiation efficiency, even with moder- ate earthing arrangements. Unlike the Windom or G5RV, the fundamental bands can be resonate