Hi Paul,
Am 28.12.2016 21:05, schrieb Paul Nicholson:
Stefan, do you have measurements, dimensions, etc of your VLF
antenna? I believe it is a wire strung between two buildings?
Sure. The wire is about 70m long and 30m above ground (average). The are
only 2 small trees below the antenna. I estimated the effective height
is 25m but since 2 years there are more buildings arround the antenna,
which lower the radiation resistance. I calculated a simplified
structure of the antenna for LF using EZNEC. Then i'm scaling down/up
the radiation resistance based on that simulation. Additionally i am
assuming a loss of 25% due to the small trees and buildings and the
feeder which is about 3m long, having almost no radiation resistance.
I can measure C ~ 480 pF.
The wire is out of stainless steel with 10mm diameter (or 12?).
You may find some more details in google maps.
Ah, and the earth resistance is very (!) low on all bands (below 500
kHz, i never tested HF there).
That's all i know. There are some more details which will affect the
radiation resistance.
My estimated radiation resistance on 2970 Hz is 70 uOhm.
With 23W and 230 mA and 230 Ohm (DC) coil losses, the ground resistance
is less than 200 Ohm on 8.27 kHz. I can measure the -3 dB bandwidth in
the next test. But for determining the ERP, we only need the antenna
current and radiation resistance of course...
> In a first test i measured 230 mA RF current and the
> power supply showed 0.94 A and 24.5 V. So that's just 23W
> including PA losses.
Should I look for a signal in my recording?
Thanks, that's not necessary at the moment.
73, Stefan
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Paul Nicholson
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