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From: "J. Allen" <vy1ja@northwestel.net>
To: <rsgb_lf_group@blacksheep.org>
References: <1GjjhM-0giu7m0@fwd29.sul.t-online.de>
Date: Tue, 14 Nov 2006 02:35:30 -0000
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Subject: Re: LF: RE: LPF coils  and VY1JA to 1W ERP
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Ha-Jo and all,

That makes sense.  There was not much difference between 80 and 155 watts, 
but I did not try anything lower and the amplifier capable higher power 
tests is under construction.   I will let everyone know what I find.

J.

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a former collegue of me had to design an amplifier in the frequency range 10 
to 20 kHz delivering a few watts. For the output filter he had used tunable 
pot cores. He was wondering that he could tune the filter just for a 
specific output level only. Changing this level would change the performance 
of the filter and required a retune of the output filter.

I could just help him by explaning that, as far as I know, all iron powder 
or ferrite coils show a certain dependance of AL value versus excitation of 
the coil. This can even be shown in a simple VFO employing either air coils 
or iron powder or ferrite coils. When the supply voltage of the oscillator 
is changed, changing oscillator power too, the influence on frequency is 
much higher when using iron powder or ferrite coils.

Therefore in the case of the low pass filter I guess the rf power will 
change the desired inductivity values slightly - I confess I do not know in 
what direction. But there should be an influence.

Assuming that the inductivity values of the output filter have been 
determined correctly, I would propose to prove this thesis at VY1JA if the 
annoying phase effect would become less when reducing power.

If this should be true, the filter coils should be retuned slightly, not the 
antenna.

HW?

73 Ha-Jo, DJ1ZB
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