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

Andrew Alford

Born Aug 5 1904 - Died Jan 25 1992 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.