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Stefan
I am talking about matching the amp 8 ohms to 50
ohms not about resonating the antenna. My antenna is already resonated for 9
Kcs, or 137 as required.
I was referring to your kite antenna and what
method you used for matching amp to antenna.
de mal/g3kev
----- Original Message -----
Sent: Tuesday, August 17, 2010 12:22
PM
Subject: Re: LF: Earth electrodes antenna
tests[Contest results]
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
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