Alford Slot antennas in theory and practise. By Mart Sakalov, SM0ERR.

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Presentation transcript:

Alford Slot antennas in theory and practise. By Mart Sakalov, SM0ERR.

Andrew Alford Born Aug Died Jan Birthplace: Samara, Russia Localizer Antenna System Patent Number(s) 2,682,050

Alford-Slot Advantages Vertical but Horizontally polarized Omni-directional Easy to build Small, light, cheap Six dBd gain ?

Babinet’s Principle “ Diffraction pattern from an opaque body is identical to that from a hole of the same size “ Note, that H and E field change place in an slot compared with a dipole.

A stealth approach. Flag pole extended with an Alford slot for 23cm.

Top ball of flag pole is removed, replaced with a rubber reduction holding the 7/8 inch hardline coax and antenna.

Bottom hinge of flag pole with the 7/8 coax burried into lawn. Not even the wife will notice this installation, stealth is the word.

35x32mm Au 750mm total 510mm slot 2,15λ 7mm gap Six dBd gain 23 cm dimentions of an Alford slot antenna

Radiation plots by courtesy Hannes Illipe SM6PGP.

23cm PA with 4xTUG delivering 400+W. Best DX using Alford slot is OK 1000+km. And, yes there was good tropo at the time.