Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-md04.r1000.mx.aol.com (Internet Inbound) with ESMTP id 82E6B380000AC; Wed, 17 Aug 2011 05:00:53 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1QtbyJ-0007TX-FL for rs_out_1@blacksheep.org; Wed, 17 Aug 2011 09:59:35 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1QtbyI-0007TO-Vf for rsgb_lf_group@blacksheep.org; Wed, 17 Aug 2011 09:59:34 +0100 Received: from imr-ma02.mx.aol.com ([64.12.206.40]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1QtbyG-0000Vi-9x for rsgb_lf_group@blacksheep.org; Wed, 17 Aug 2011 09:59:34 +0100 Received: from mtaomg-ma02.r1000.mx.aol.com (mtaomg-ma02.r1000.mx.aol.com [172.29.41.9]) by imr-ma02.mx.aol.com (8.14.1/8.14.1) with ESMTP id p7H8xQXm029157 for ; Wed, 17 Aug 2011 04:59:26 -0400 Received: from core-msb005b.r1000.mail.aol.com (core-msb005.r1000.mail.aol.com [172.29.233.147]) by mtaomg-ma02.r1000.mx.aol.com (OMAG/Core Interface) with ESMTP id 46EE7E000082 for ; Wed, 17 Aug 2011 04:59:26 -0400 (EDT) References: <68BE37BD69E54DEE89CEBA8E30E9B94E@PcMinto> <4E47FFE9.10100@iup.uni-heidelberg.de> <3ED8E5422F1F45DBB8186E9D9870AD63@PcMinto> <4E480E02.9020706@iup.uni-heidelberg.de> <938BF599006244949F6CDDB5BA91F347@PcMinto> <4E482FBD.7030402@freenet.de> <4E484183.9090805@iup.uni-heidelberg.de> <4E494A57.90105@freenet.de> <4E4956DA.1060201@iup.uni-heidelberg.de> <4E49643E.5090708@freenet.de> <4E496FF9.4040608@iup.uni-heidelberg.de> <0A4ED65EC3B244A3BD0DAD6ACFF43793@JimPC> <4E4A5597.4070709@iup.uni-heidelberg.de> <3746D901368F4C139E414F9110153EEE@JimPC> <4E4A9A1F.2060600@iup.uni-heidelberg.de> <1B55B625C3CD4D529EC361D9C5D79D96@JimPC> <4E4AD4C8.8000509@iup.uni-heidelberg.de> <4E4AEF31.5010306@iup.uni-heidelberg.de> <1FF2FAD9854F4890A338A9F862D93FE9@JimPC> To: rsgb_lf_group@blacksheep.org In-Reply-To: <1FF2FAD9854F4890A338A9F862D93FE9@JimPC> X-MB-Message-Source: WebUI MIME-Version: 1.0 From: Markus Vester X-MB-Message-Type: User X-Mailer: AOL Webmail 34047-STANDARD Received: from 194.138.39.56 by Webmail-m104.sysops.aol.com (64.12.224.158) with HTTP (WebMailUI); Wed, 17 Aug 2011 04:59:26 -0400 Message-Id: <8CE2AD319756ED7-1C20-14370@Webmail-m104.sysops.aol.com> X-Originating-IP: [194.138.39.56] Date: Wed, 17 Aug 2011 04:59:26 -0400 (EDT) X-AOL-SCOLL-SCORE: 0:2:453161792:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-Spam-Score: 0.3 (/) X-Spam-Report: autolearn=disabled,FORGED_AOL_TAGS=0.281,HTML_MESSAGE=0.001,UNPARSEABLE_RELAY=0.001 Subject: Re: LF: Ferrite RX antennas Content-Type: multipart/alternative; boundary="--------MB_8CE2AD31983B717_1C20_433F9_Webmail-m104.sysops.aol.com" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.1 required=5.0 tests=FORGED_AOL_TAGS, HTML_FONTCOLOR_UNKNOWN,HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G X-AOL-SCOLL-SCORE: 0:2:477059168:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1d60584e4b8345389e X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none This is a multi-part message in MIME format. ----------MB_8CE2AD31983B717_1C20_433F9_Webmail-m104.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Stefan, Jim, you could increase the signal bandwidth without compromising SNR by connect= ing a low impedance preamplifier. This technique has been used widely and s= uccessfully in magnetic resonance imaging ("preamp decoupling"). The preamp= is designed to have an input impedance that differs largely from the noise= -optimum source impedance, so that you can preserve the noise match but cre= ate an intentional signal mismatch. In practice, you would still want to use a low-noise FET connected to the h= igh impedance point of a parallel resonant antenna. Normally the gate input= impedance (megohms) is higher than the noise optimum (tens of kiloohms), s= o you would have no preamp damping at all. The trick is then to lower the i= nput impedance by lossless feedback, which has neglegible effect on the noi= se parameters.=20 One configuration is a compromise between common source and common gate cir= cuit configuration ("Zwischenbasisschaltung"), which can be realised by ins= erting an additional negative-feedback winding in the source-to-ground path= . This is similar to the old regenerative audion, but with the feedback coi= l polarity reversed. Another configuration is parallel feedback from drain = to gate, by intentionally increasing the Miller capacitance. Best regards, Markus (DF6NM) -----Urspr=C3=BCngliche Mitteilung-----=20 Von: James Moritz An: rsgb_lf_group Verschickt: Mi, 17 Aug 2011 1:13 am Betreff: Re: LF: Ferrite RX antennas Dear Stefan, Looking good so far... A Q of 486 is certainly reaching the point where it becomes inconvenient -= =20 ut remember that it is easy to reduce Q (probably connecting a preamp,=20 utting it in a container, etc, will reduce Q a bit anyway), and that the=20 igher Q is, the better the SNR. So I would test it as an antenna with a=20 reamp - if there is more SNR than you need, you could experiment with some= =20 amping resistance. Cheers, Jim Moritz 3 de M0BMU=20 ----------MB_8CE2AD31983B717_1C20_433F9_Webmail-m104.sysops.aol.com Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset="utf-8"
Stefan, Jim,
 
you could increase the signal bandwidth without compromising SNR by co= nnecting a low impedance preamplifier. This technique has been used wi= dely and successfully in magnetic resonance imaging ("preamp decoupling").&= nbsp;The preamp is designed to have an input impedance that differs largely= from the noise-optimum source impedance, so that you can preserve the nois= e match but create an intentional signal mismatch.
 
In practice, you would still want to use a low-noise FE= T connected to the high impedance point of a parallel resonant antenna. Nor= mally the gate input impedance (megohms) is higher than the noise opti= mum (tens of kiloohms), so you would have no preamp damping at all. The tri= ck is then to lower the input impedance by lossless feedback, which ha= s neglegible effect on the noise parameters.
 
One configuration is a compromise between common source and common gat= e circuit configuration ("Zwischenbasisschaltung"), which can be reali= sed by inserting an additional negative-feedback winding in the source-to-g= round path. This is similar to the old regenerative audion, = but with the feedback coil polarity reversed. Another configuration is para= llel feedback from drain to gate, by intentionally increasing the Miller ca= pacitance.

Best regards,
Markus (DF6NM)
= -----Urspr=C3=BCngliche Mitteilung-----
Von: James Moritz <james.moritz@btopenworld.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Mi, 17 Aug 2011 1:13 am
Betreff: Re: LF: Ferrite RX antennas

Dear S=
tefan,

Looking good so far...

A Q of 486 is certainly reaching the point where it becomes inconvenient -=
=20
but remember that it is easy to reduce Q (probably connecting a preamp,=20
putting it in a container, etc, will reduce Q a bit anyway), and that the=
=20
higher Q is, the better the SNR. So I would test it as an antenna with a=20
preamp - if there is more SNR than you need, you could experiment with some=
=20
damping resistance.

Cheers, Jim Moritz
73 de M0BMU=20
----------MB_8CE2AD31983B717_1C20_433F9_Webmail-m104.sysops.aol.com--