HI All,
Today we finished installing a vertical with a top hat at HG0R, but it
is not perfect (yet).
The vertical part is about 20.5m (67 ft) tall, starts with 10m of 50mm
(2") pipe at the bottom, and ends with 28mm (1.1") OD pipe on top.
There are 8 quarter-wave radials below the antenna at each 45 degs, soil
is wet black earth.
Top hat wires are connected to a small aluminum plate. The four (4) top
hat wires are about 12m (39 ft) long each, and are sloping at an angle
between 60 and 45 degrees.
We measured the antenna, and found the following:
*1904 kHz* (minimum SWR and also ain inflexion point in phase):
*Z=68.1 + j0.3 SWR 1:1.36 Phase 0 deg*
*1844 kHz* (resisitive Z closest to 50 ohms)
*Z=48.9 + j21.5 SWR 1:1.54 Phase 23 degs*
*/One step before, with shorter top hat wires (approx. 10.2m wires) the
SWR was lower at the 0 phase point, but it was at 2005 kHz./*
Please tell me what shall we do:
- tilt the antenna again, add more lengths to the top hat wires, so that
phase 0 point comes down to about 1840 kHz (R will be still higher than
50 ohms), and add more radials, perhaps radiation resiastance comes
closer to 50 ohms?
- add a series capacitor to compensate the +j21.5 at 1844 kHz, and leave
it as is?
Or any aother suggestions?
73/DX
Steve HA0DU
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