Alford Slot antenna for 1.3GHz operation

The slotted cylinder antenna, Alford Slot, was first introduced by Andrew Alford in 1946. Its an omnidirectional horizontally polarized antenna. Performance of this antenna have been measured with some simple homemade equipment and a PC. All measurements done at 1296.8 MHz using a VCO (locked to a 13 MHz reference), a logarithmic detector from Analog devices AD8313 connected to an A/D converter. The A/D converter is connected to the PC parallel port, the antenna rotator is also controlled by the parallel port.

Dimensions given in G3JVL/G5YGF/G4KNZ paper

Antenna type    Tube dimensions            Slot width(mm) Slot lenght(mm)
End fed           31.8 mm OD, 20swg wall      4            510
End fed           35.0 mm OD, 1.1mm wall      8            510
End fed           38.1 mm OD, 16swg wall     11            510
Center Fed        31.8 mm OD, 20swg wall      4            510
Center Fed        35.0 mm OD, 1.1mm wall      8            510
Center Fed        38.1 mm OD, 16 swg wall    11            510