The below projects came up after an e-mail exchange with Colin, who had some 300 Ohm stuff to test. So they're run for a folded dipole radiator. First at all I must explain that the Nec-2 software is quite reliable when dealing with radiation patterns, but can be easily deceived about feed-point impedance. And the analysis of the folded dipole is not a reccomended one. The usual workaround is to run the analysis with a standard dipole, then multiply by 4 the resulting impedance.

To feed our antenna without acrobatics, I think we've got three choices:

- obtain a 50 Ohm resistance and feed direct
- obtain one around 100 Ohm and feed thru a 75 Ohm 1/4 wl transformer
- obtain a 200 Ohm resistance and use a 4/1 balun

Anywhy here the first one. Take note of the 20mm diameter of the radiator, to simulate the folding.

reflector | at 0.000 m. | diameter 02mm | 5.42m |

driver | at 1.000 m. | diameter 20mm | 5.20m |

director | at 2.710 m. | diameter 02mm | 5.10m |

The antenna should have a feed impedance of 12.2 -j.49 ohms.

I already built it with standard electric wire, insulated, so I
shortened the actual length by a -3% factor. When I'll find the
time and the right qth to test it, I'll let you know the results.

But now here the second one.

reflector | at 0.000 m. | diameter 02mm | 5.60m |

driver | at 1.360 m. | diameter 20mm | 5.26m |

director | at 2.710 m. | diameter 02mm | 5.05m |

That should have a feed impedance of 33.5 +j.84 ohms. If the driven element is a folded dipole, use 1/4 transformer. But if you don't fear a 1/1.5 swr -I don't- then use as driver a simple wire with 5.32m length.

Hi. Paolo 1839