Alford Slot antennas in theory and practise. By Mart Sakalov, SM0ERR.
Andrew Alford Born Aug 5 1904 - Died Jan 25 1992 Birthplace: Samara, RussiaLocalizer Antenna SystemPatent 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
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.