Mal,
Are you talking about a earth electrode antenna or your vertical
antenna? I assume you mean the vertical ;-)
You will get several kV, most probably above 10 kV rms on your antenna.
That's why a ferrite transformer is not a good choice for a large ( C )
antenna in addition with QRO! For your 5 W tests it may work with a
ferrite coil L but not at 500 W and above.
There is no alternative to wind an air coil if you want to
generate a signal that can be watched in the far field.
And if you want to generate a signal that can be heared in CW across EU
i recommend a power supply like i had as i worked in Darmstadt last
year: http://www.hst.tu-darmstadt.de/index.php?id=173&L=1 ;-)
Transforming to 50 Ohm is not wrong but it is not necessary. You can
just resonate the antenna and match the load to something suitable for
the audio amp (4...8 Ohm). A 50 Ohm impedance level is just necessary
if you want to filter your signal with a precise dimensioned low pass
filter that properly works at 50 Ohm input and output impedance (in my
opinion). Essential is, that the power is pushed into the antenna! ;-)
73, Stefan
PS: On an earth antenna, which is not resonated (!), you just have to
apply a proper output voltage to the antenna that causes the DC input
power at the PA that you want to generate.
Am 17.08.2010 12:51, schrieb mal hamilton:
Stefan
What method do u use to couple the amplifier to the electrodes? Is the amp
output impedence 8 ohms.
My method for my antenna using an audio amp would be to use a ferrite
transformer to step up the 8 ohms to 50 ohms (x 6.250) turns Prim 8 and
Secondary 20 turns. This way I can use my existing test equipment for swr
etc.
mal/g3kev
|
|
