Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-mk06.r1000.mx.aol.com (Internet Inbound) with ESMTP id 03E7D380001A2; Sun, 21 Aug 2011 12:03:00 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1QvASt-0002GJ-12 for rs_out_1@blacksheep.org; Sun, 21 Aug 2011 17:01:35 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1QvASs-0002GA-3U for rsgb_lf_group@blacksheep.org; Sun, 21 Aug 2011 17:01:34 +0100 Received: from mail-gw0-f43.google.com ([74.125.83.43]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1QvASp-0004sL-KQ for rsgb_lf_group@blacksheep.org; Sun, 21 Aug 2011 17:01:34 +0100 Received: by gwm11 with SMTP id 11so3366794gwm.16 for ; Sun, 21 Aug 2011 09:01:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=VR5UYAkMO6FQ0blDkaRnKG2I3e5f8h4TqKlP/Y8ZIN0=; b=b7hdzLdlAZByvLYCmU6rgrv5YB+1+3cBobYCXsLOSvP2X1Js2OkzOLSAvLy/rBCWkr 9jaS/SDDfv3WBzDOu5LdHiPVYQ+EfDRBYHfwZXOzrxLkGGrX/ImZUX2SM3pRW+dRd9nP mFTa39RICzYoBvHWKCdIQykt0HUNiUHNpuB4g= MIME-Version: 1.0 Received: by 10.147.11.11 with SMTP id o11mr1357163yai.4.1313942484579; Sun, 21 Aug 2011 09:01:24 -0700 (PDT) Received: by 10.147.125.14 with HTTP; Sun, 21 Aug 2011 09:01:24 -0700 (PDT) In-Reply-To: <00f801cc6004$c2282bd0$1502a8c0@Clemens04> References: <16BC8B3CA8672445BC2A29B4C14A26D4379ED2AAB4@exlnmb01.eur.nsroot.net> <4DF9EFD1.5010208@iup.uni-heidelberg.de> <1313780109.51443.YahooMailNeo@web111907.mail.gq1.yahoo.com> <9CD1E11E8BC9402CB4AECECAC4088443@JimPC> <00f801cc6004$c2282bd0$1502a8c0@Clemens04> Date: Mon, 22 Aug 2011 02:01:24 +1000 Message-ID: From: Tony Magon To: rsgb_lf_group@blacksheep.org X-Spam-Score: 0.9 (/) X-Spam-Report: autolearn=disabled,HTML_10_20=0.945,HTML_MESSAGE=0.001 Subject: Re: LF: Re: Re: Ferrite wideband antennas? Content-Type: multipart/alternative; boundary=001517493d440c759504ab061377 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=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: 0:2:504309792:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d225.2 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1d618a4e512c331a7e X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none --001517493d440c759504ab061377 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi All This article may be of interest http://gmweb2.net/The%20FS%20Loop.htm 73 Tony VK2IC On Sun, Aug 21, 2011 at 11:18 PM, Clemens Paul wrote: > Antenna engineers use to say about design goal limits of antennas: > > Small > Efficient > Wideband > > Pick any two (meaning you can't have all three...). > > 73 > Clemens > DL4RAJ > > ----- Original Message ----- From: "James Moritz" < > james.moritz@btopenworld.com> > To: > Sent: Saturday, August 20, 2011 12:07 PM > Subject: LF: Re: Ferrite wideband antennas? > > > Dear Daniele, LF Group, >> >> Regarding bandwidth, the first thing to note is that the same principles >> essentially apply to both air-cored loop and ferrite rod cored loop ante= nnas >> - the main difference is that air-cored loops are wide and flat, but fer= rite >> rods are long and thin ;-). >> >> Assuming you can make a preamp with a low enough noise level, the minimu= m >> usable signal level "sensitivity" of a loop antenna depends on the ratio >> between the induced signal level, and the level of thermal noise produce= d by >> the resistance of the loop windings, core losses, etc. So this sensitivi= ty >> depends on the construction and size of the loop/rod, and in principle i= t >> does not matter if it is tuned for narrow-band resonance or loaded to >> produce wide bandwidth, provided the tuning or loading arrangements do n= ot >> introduce additional noise. But in practice, tuning/loading and >> preamplifiers will introduce some additional noise. >> >> The big advantage of a tuned loop is that the resonant circuit can provi= de >> a high "passive gain". So Stefan's rod antenna probably produces an EMF = in >> the nanovolt range for usable received signal levels, but the high Q cir= cuit >> it forms with a parallel capacitor increases this voltage by more than 5= 0dB >> The actual signal power level is not increased by the resonant circuit, = but >> the much higher signal voltage is easily handled by a simple preamplifie= r >> with insignificant additional noise introduced. The resonant circuit als= o >> has a very narrow bandwidth - this might be an advantage for attenuating >> strong out-of-band signals, but is a drawback if wideband reception is >> required, or remote tuning of the loop is needed. >> >> In many commercially available wideband loops, the loop is loaded by a >> preamp with a very low input impedance. This provides a flat frequency >> response, since the loop EMF rises in proportion to signal frequency, bu= t >> the signal current at the preamplifier input is maintained constant by t= he >> reactance of the loop inductance, which also rises proportional to >> frequency. This flat response is very popular for measuring applications= and >> wideband reception. But the preamp design is much more difficult, becaus= e >> the input signal amplitude is effectively attenuated by the combination = of >> high loop reactance and low preamp input impedance. So careful preamp de= sign >> is needed, to provide a low input impedance, very low noise voltage, and= a >> low noise figure when fed from a highly mis-matched, relatively much hig= her >> source impedance. The "noiseless feedback" techniques such as "Zwichenba= sis" >> amplifiers mentioned by DF6NM or "Norton" feedback amplifiers can be >> usefully used. But even with careful preamp design, relatively large loo= ps >> (~1m) seem to be neccessary to achieve a reasonable sensitivity. Of cour= se, >> if loop size is not an issue, one can simply increase the loop area to >> produce a greater signal amplitude, and all that is needed is a large wi= re >> loop terminated by a low impedance receiver input. >> >> In my view, for communications reception purposes, creating a flat outpu= t >> voltage vs. field strength relationship for a wideband loop is not >> particularly useful - the background noise field strength decreases with >> frequency, so if you keep the "natural" signal EMF-proportional-to-frequ= ency >> response of a loop, the background noise at the receiver input remains >> fairly constant with frequency. I have used 2x2m and 4 x 5m loop antenna= s >> where the loop inductance forms the input inductor of a low-pass filter = with >> cut-off frequency of about 550kHz, in order to attenuate powerful broadc= ast >> signals. These give reasonable results from VLF to 500kHz without any tu= ning >> adjustments. >> >> Cheers, Jim Moritz >> 73 de M0BMU >> >> >> >> ----- >> eMail ist virenfrei. >> Von AVG =FCberpr=FCft - www.avg.de >> Version: 10.0.1392 / Virendatenbank: 1520/3835 - Ausgabedatum: 15.08.201= 1 >> > > > --001517493d440c759504ab061377 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi All

This article may be of interest

http://gmweb2.net/The%20FS%20Loop.htm
73

Tony VK2IC

On Sun, Aug 21, 20= 11 at 11:18 PM, Clemens Paul <cpaul@gmx.net> wrote:
Antenna engineers use to say about design g= oal limits of antennas:

Small
Efficient
Wideband

Pick any two (meaning you can't have all three...).

73
Clemens
DL4RAJ

----- Original Message ----- From: "James Moritz" <james.moritz@btopenw= orld.com>
To: <r= sgb_lf_group@blacksheep.org>
Sent: Saturday, August 20, 2011 12:07 PM
Subject: LF: Re: Ferrite wideband antennas?


Dear Daniele, LF Group,

Regarding bandwidth, the first thing to note is that the same principles es= sentially apply to both air-cored loop and ferrite rod cored loop antennas = - the main difference is that air-cored loops are wide and flat, but ferrit= e rods are long and thin ;-).

Assuming you can make a preamp with a low enough noise level, the minimum u= sable signal level "sensitivity" of a loop antenna depends on the= ratio between the induced signal level, and the level of thermal noise pro= duced by the resistance of the loop windings, core losses, etc. So this sen= sitivity depends on the construction and size of the loop/rod, and in princ= iple it does not matter if it is tuned for narrow-band resonance or loaded = to produce wide bandwidth, provided the tuning or loading arrangements do n= ot introduce additional noise. But in practice, tuning/loading and preampli= fiers will introduce some additional noise.

The big advantage of a tuned loop is that the resonant circuit can provide = a high "passive gain". So Stefan's rod antenna probably produ= ces an EMF in the nanovolt range for usable received signal levels, but the= high Q circuit it forms with a parallel capacitor increases this voltage b= y more than 50dB The actual signal power level is not increased by the reso= nant circuit, but the much higher signal voltage is easily handled by a sim= ple preamplifier with insignificant additional noise introduced. The resona= nt circuit also has a very narrow bandwidth - this might be an advantage fo= r attenuating strong out-of-band signals, but is a drawback if wideband rec= eption is required, or remote tuning of the loop is needed.

In many commercially available wideband loops, the loop is loaded by a prea= mp with a very low input impedance. This provides a flat frequency response= , since the loop EMF rises in proportion to signal frequency, but the signa= l current at the preamplifier input is maintained constant by the reactance= of the loop inductance, which =A0also rises proportional to frequency. Thi= s flat response is very popular for measuring applications and wideband rec= eption. But the preamp design is much more difficult, because the input sig= nal amplitude is effectively attenuated by the combination of high loop rea= ctance and low preamp input impedance. So careful preamp design is needed, = to provide a low input impedance, very low noise voltage, and a low noise f= igure when fed from a highly mis-matched, relatively much higher source imp= edance. The "noiseless feedback" techniques such as "Zwichen= basis" amplifiers mentioned by DF6NM or "Norton" feedback am= plifiers can be usefully used. But even with careful preamp design, relativ= ely large loops (~1m) seem to be neccessary to achieve a reasonable sensiti= vity. Of course, if loop size is not an issue, one can simply increase the = loop area =A0to produce a greater signal amplitude, and all that is needed = is a large wire loop terminated by a low impedance receiver input.

In my view, for communications reception purposes, creating a flat output v= oltage vs. field strength relationship for a wideband loop is not particula= rly useful - the background noise field strength decreases with frequency, = so if you keep the "natural" signal EMF-proportional-to-frequency= response of a loop, the background noise at the receiver input remains fai= rly constant with frequency. I have used 2x2m and 4 x 5m loop antennas wher= e the loop inductance forms the input inductor of a low-pass filter with cu= t-off frequency of about 550kHz, in order to attenuate powerful broadcast s= ignals. These give reasonable results from VLF to 500kHz without any tuning= adjustments.

Cheers, Jim Moritz
73 de M0BMU



-----
eMail ist virenfrei.
Von AVG =FCberpr=FCft - www= .avg.de
Version: 10.0.1392 / Virendatenbank: 1520/3835 - Ausgabedatum: 15.08.2011 <= br>



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