At 11:21 AM 2008-09-24, OZ1AXG Flam wrote:
>A question about wire ...
>I have constructed a 3/8 for 160 meter. I use the tower to support the
>antenna. It runs 22 meter vertically and then (horisontal for 24,5 meters
>(i.e. total 46.5 meter). distance from tower is 1 meter.
>A the base of the antenna it is feed with a serial capacitor of 430 pF (a
>330 in parallel with a 100pF : both door noob).
>Ground is a combination of 4 ground rods and wire (space is limited). Best
>swr @ 1860 Khz is 1:1.4. 1:2 bandwidth is app 80KHz. A noise bridse have
>shown impedans around 70+j1.
>Currently the wire is 1.5mm stainless steel wire.
>How much would the antenna be improved if i substitute the SS wire with with
>1.5mm braided copper wire?
>I guess the seial capacitor would change as well ? any idea how much ?
>Antennewire i use ( steel 40050 and copper: 40051):
I modeled this with EZNEC (without the tower) and assumed the 1.5 mm
diameter stainless steel wire has a resistivity of 7.2 e-7 ohm-m and
relative permeability of 1.02. I estimated about 20 ohms of ground
loss resistance. Here's what happens at 1860 kHz:
Cu G=-0.43 dBi Z=52.6 -j 46.6 SWRmin=1.13 at 1922 kHz BW=97
kHz (50 ohm SWR 2:1)
SS G=-1.48 dBi Z=68 -j 36.2 SWRmin=1.44 at 1907 kHz BW=90 kHz
The adjacent tower will modify these values depending on where it is
resonant, cross section, etc.
With copper, you should get about 1 dB more signal, a better match to
50 ohms, and resonance moved up about 15 kHz. Adding another 27 pF
in parallel (457 pF total) should restore the resonant point.
73, Terry N6RY
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