Re: LF: About 9khz loop...Re: R: Re: R: To Stefan/DK7FC Re: AW: E-field probe antennas for dreamers band?

[Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>]

Hi George,


Am 07.04.2010 08:34, schrieb George Vastianos:
> About the easyloop end 9 khz bf, never forget that: "A filter works 
> correct and has the frequency responce that it was designed for... 
> when the input and output impedance is matched with the circuits 
> before and after the filter" This means that a filter is not a black 
> box where you plug it somewhere and plays... you have to look 
> carefully and check if the bandpass of Jim's loop can fit inside your 
> easyloop amp.
Jim' switchable filter has a non-inverting OP amp as an input. So, the 
input impedance of the filter can be seen as infinity, especially at 9 
kHz. Also, the filter behaviour is not affected by the circuit that is 
connected before the OP amp (IC1B). It is decoupled by the OP amp. Also 
the input impedance of the next stage, IC1A and it's input R divider is 
about 50 kOhm, what is high against R11 (1,2kOhm). So the filter is not 
affected by it's outside components of the circuit and/or the kind of 
loop antenna that you connect at the input, i would say.
If using different loop antenna forms at the input it may just be 
necessary to adjust C8 for optimal resonance.
73, Stefan/DK7FC