70 cm - 3 cm Beacon Antennas
In 1999 I designed a set of waveguide double-slot antennas for 13 cm
to 3 cm
beacons and an Alford slot antenna (slotted cylinder antenna) for 23 cm
beacon
as a part of a "Beacon '99
Project".
The design was published in the "Beacon '99 Project" Proceedings
and two PDF files describing those antennas can also be downloaded here:
- Waveguide Double-Slot Antennas (13, 9,
6, 3 cm) -
200k - Standard aluminium rectangular tubes are used as standard
waveguides are not so easy obtainable by amateurs. All the antennas
have approximately the same length so that the mounting structure and
the radome can be the same regardless of the frequency band. There are
3 double-slots for 13cm, 4 for 9 cm, 8 for 6 cm and 12 for 3 cm.
Various pictures showing the manufactured antenna parts and antennas
can be viewed on the Beacon '99
Homepage. (There is a typo in the original text - the slot length
in the Table 2 is designated with
the character l instead of l . Also the data for the waveguide to
coax
transition monopole diameter is missing - it should be 2,0 mm but it is
not critical at all.)
As a by product the 70 cm beacon Alford slot antenna was designed.
Mechanical
dimensions are as follows with the reference to the drawing of the 23
cm
antenna:
- tube outer diameter: 100 mm
- wall thickness: 1 mm
- slot length: 675 mm
- slot width: 6 mm
- feeding point is not at the center of the slot but 200 mm from
one end of the slot.
- feeding point impedance is ~50 ohm so only the 1:1 balun is used
with 122 mm long stub made from the same cable as used for feeding the
antenna (RG-188 or RG-316).