Stefan thanks for the info...
You are 100% correct. I didnt spent time to study much the easy loop. I
wrote what i wrote just because if we want to be very accurate on what we
say the filter starts from C12 and ends on C14 and its completly passive.
The IC1B it is just an OP that works as "buffer" with some gain ...(in
theory buffer has unity gain and in our case we have 9db gain) so it is not
part of the filter and is used to "isolate" the previous stage from the next
stage IC1A. The idea behind buffers is that the next stage must have at
least 10 times higher input impedance from the previous stage and since the
differential inputs of the op amps have input resistance of several Mohms
are ideal for that use... That is why I wrote word "matched" and not the
"same impedance". I dont know what Daniele means when he talks about the
filter (if he means the passive part or with the amplifier in front). If he
talks about the filter it self (passive) then he may have problems and
depends from components around the output of the amp of easyloop. In case he
reproduce from IC1B to the end then he will reproduce the 80% of Jims
Loop... so in this case why not build it all??? BTW iam sure your comments
will give a clear picture to Daniele of whats going on...
73
sv8gxc
----- Original Message -----
From: "Stefan Schäfer" <[email protected]>
To: <[email protected]>
Sent: Wednesday, April 07, 2010 11:18 AM
Subject: Re: LF: About 9khz loop...Re: R: Re: R: To Stefan/DK7FC Re: AW:
E-field probe antennas for dreamers band?
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
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