Message-ID: <000901cad63c$cdc63020$0101a8c0@amd4800>
From: "George Vastianos" <george@vastianos.com>
To: <rsgb_lf_group@blacksheep.org>
References: <MFEJIKCLCMPDFHOKMANAGEIPOFAA.paulc@snet.net> <001c01cad439$aa7aa830$0101a8c0@amd4800> <38A51B74B884D74083D7950AD0DD85E82A1BD5@File-Server-HST.hst.e-technik.tu-darmstadt.de> <003801cad57e$a13410e0$0101a8c0@amd4800> <8585FA1C733D9A42AEA98C724D8FB811C05393@FBCMST18V01.fbc.local> <002301cad597$6b32cdb0$0101a8c0@amd4800> <8585FA1C733D9A42AEA98C724D8FB811C05394@FBCMST18V01.fbc.local> <001901cad61c$5ffbdb50$0101a8c0@amd4800> <4BBC3FC1.5070806@iup.uni-heidelberg.de>
Date: Wed, 7 Apr 2010 13:26:33 +0300
MIME-Version: 1.0
Subject: Re: LF: About 9khz loop...Re: R: Re: R: To Stefan/DK7FC Re: AW: E-field probe antennas for dreamers band?
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Stefan thanks for the info...

You are 100% correct. I didnt spent time to study much the easy loop.=
 I=20
wrote what i wrote just because if we want to be very accurate on what=
 we=20
say the filter starts from C12 and ends on C14 and its completly passi=
ve.=20
The IC1B it is just an OP that works as "buffer" with some gain ...(in=
=20
theory buffer has unity gain and in our case we have 9db gain) so it=
 is not=20
part of the filter and is used to "isolate" the previous stage from th=
e next=20
stage IC1A. The idea behind buffers is that the next stage must have=
 at=20
least 10 times higher input impedance from the previous stage and sinc=
e the=20
differential inputs of the op amps have input resistance of several Mo=
hms=20
are ideal for that use... That is why I wrote word "matched" and not=
 the=20
"same impedance". I dont know what Daniele means when he talks about=
 the=20
filter (if he means the passive part or with the amplifier in front).=
 If he=20
talks about the filter it self (passive) then he may have problems and=
=20
depends from components around the output of the amp of easyloop. In=
 case he=20
reproduce from IC1B to the end then he will reproduce the 80% of Jims=
=20
Loop... so in this case why not build it all??? BTW iam sure your comm=
ents=20
will give a clear picture to Daniele of whats going on...

73

sv8gxc



----- Original Message -----=20
From: "Stefan Sch=E4fer" <Stefan.Schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, April 07, 2010 11:18 AM
Subject: Re: LF: About 9khz loop...Re: R: Re: R: To Stefan/DK7FC Re:=
 AW:=20
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 blac=
k
>> 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 yo=
ur
>> 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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