Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-mp05.r1000.mx.aol.com (Internet Inbound) with ESMTP id 7DB7838000091; Mon, 29 Aug 2011 14:09:36 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Qy6GW-0001jc-G6 for rs_out_1@blacksheep.org; Mon, 29 Aug 2011 19:08:56 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Qy6GV-0001jT-Oh for rsgb_lf_group@blacksheep.org; Mon, 29 Aug 2011 19:08:55 +0100 Received: from nm7.bullet.mail.sp2.yahoo.com ([98.139.91.77]) by relay1.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1Qy6GT-00024b-Ig for rsgb_lf_group@blacksheep.org; Mon, 29 Aug 2011 19:08:55 +0100 Received: from [98.139.91.69] by nm7.bullet.mail.sp2.yahoo.com with NNFMP; 29 Aug 2011 18:08:47 -0000 Received: from [98.139.91.58] by tm9.bullet.mail.sp2.yahoo.com with NNFMP; 29 Aug 2011 18:08:47 -0000 Received: from [127.0.0.1] by omp1058.mail.sp2.yahoo.com with NNFMP; 29 Aug 2011 18:08:47 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 75545.8552.bm@omp1058.mail.sp2.yahoo.com Received: (qmail 14299 invoked by uid 60001); 29 Aug 2011 18:08:46 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s1024; t=1314641326; bh=mVsA6Ir+eQxxE082LMTsxwpaGfbdHUcSIFcRlu4TRSI=; h=X-YMail-OSG:Received:X-Mailer:References:Message-ID:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=g2UKbbps3zdKS2S+5OJnaL8wB95VcmAv4Nl4O28HOA8D86FkoBDg6ce0ft2s08jdi5kDDv0o5Ux11/5Kt++GTh3Ns+vvMKuinAGe6P3WhuTbqMYR0hQ26jRnTnNe7HTespuhWeDFUQAIHvR1jDh+m6h1mcYLTRt7kzfCcJVBk20= DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Mailer:References:Message-ID:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=mrangiRGCW3pTIXhrAk+zGgIYUiHVU68COKDNCk9/DTfpy1n6xxiEFeU5RagWtVbSbs5pUCZ3VNa8SBX39TZZJyeD57VE2DKiIYBLlKFKMFv+TRBN1kIgjy40R8jzihAny4pSi+0IRqNyTK1BSzeLboXFxVh3T5NPAvV0KeHEC4=; X-YMail-OSG: c7.CmrAVM1kNkwoPFMmcnxpPvlUJzTxpsCrKVSwUzOyZkjn jzsdDko2tLD.X9L9_mDk06IvyyB89Y9wazFg_zmVKj9s3Vms5x8EXkHGOTO7 .egl5yYZVJ4km2kFwnrBWEvV2XKXGIbgZvYLtwEbGv8rIzLEPYkqjO_Yl7CN hQUQhJu9Zcc6gXLru4BMNSkpEfq43o1Uw06I7skLFMSsS_wtOYsKcfiVlEXU j5DzAcWP.ghylnqd7_22ApwrgEXZBdxHm_JoQLtwXuwqYllkOxnzK4ZaUS63 WkQN9fb50MIfLglY6HgUesqX95pwhg2LRqk2O5CIXYd9WDqrd3nuTs9wce.x wY1KUJXOEjC7Y_J52Ny5EliCF.WzEiFIqVp8TFLqTc4V0J9_d Received: from [151.99.187.181] by web111910.mail.gq1.yahoo.com via HTTP; Mon, 29 Aug 2011 11:08:46 PDT X-Mailer: YahooMailWebService/0.8.113.315625 References: <16BC8B3CA8672445BC2A29B4C14A26D4379ED2AAB4@exlnmb01.eur.nsroot.net> <4DF9EFD1.5010208@iup.uni-heidelberg.de> <1313780109.51443.YahooMailNeo@web111907.mail.gq1.yahoo.com> <9CD1E11E8BC9402CB4AECECAC4088443@JimPC> <1314394178.5030.YahooMailNeo@web111905.mail.gq1.yahoo.com> <1314641183.5605.YahooMailNeo@web111910.mail.gq1.yahoo.com> Message-ID: <1314641326.93643.YahooMailNeo@web111910.mail.gq1.yahoo.com> Date: Mon, 29 Aug 2011 11:08:46 -0700 (PDT) From: Daniele Tincani To: "rsgb_lf_group@blacksheep.org" In-Reply-To: <1314641183.5605.YahooMailNeo@web111910.mail.gq1.yahoo.com> MIME-Version: 1.0 DomainKey-Status: good (testing) X-Spam-Score: 1.4 (+) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,HTML_TINY_FONT=1.425 Subject: Re: LF: Re: Ferrite wideband antennas? Content-Type: multipart/alternative; boundary="0-771395587-1314641326=:93643" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=1.0 required=5.0 tests=FORGED_YAHOO_RCVD,HTML_20_30, HTML_MESSAGE,TO_ADDRESS_EQ_REAL 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: 0:2:489968864:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m225.2 ; domain : yahoo.com DKIM : fail x-aol-sid: 3039ac1dc1494e5bd5df65a4 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none --0-771395587-1314641326=:93643 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable =A0=0A"all of view" meant "all of you"...=0A=A0=0A=0AFrom: Daniele Tincani = =0ATo: "rsgb_lf_group@blacksheep.org" =0ASent: Monday, August 29, 2011 8:06 PM=0ASubject: Re: = LF: Re: Ferrite wideband antennas?=0A=0A=0A=A0=0AHello Jim, LF,=0A=A0=0Atha= nks to all of view for feedbacks to my inquiry.=0A=A0So my rough summary is= :=0A- small-size (e.g. ferrite cored) loops need tuning =3D high Q to provi= de a reasonable signal level.=0A- intermediate-size (e.g. 1m diameter or so= ) loops can be wide-band but require=A0low-noise, very low-impedance pre-am= ps.=0A- bigger loops (e.g. > 2m diameter) can be wide-band even when connec= ted directly=A0to a low-impedance receiver input=A0(without a pre-amplifier= ), may be through a broadband transformer to furtherly reduce the load impe= dance as seen by the loop.=0A=A0=0AIn general, loop size is more important = for sensitivity than permeability of core material=A0and number of turns.= =0A=A0=0AFor practical reasons,=A0for rx activity at home I'm building a ~1= m wide-band loop. The reference design for the amplifier is M0AYF's (despit= e it is not a very low-impedance pre-amp, I think).=0A=A0=0ANevertheless, t= he discussion about ferrite-cored antennas here on the reflector is more an= d more pushing me to build my own "loopstick" and experiment with it.=0ACou= ld it be possible to tune a ferrite loop over a frequency range as wide as = 100-500KHz? Or at least over the EU NDB band (say 300-500KHz)?=0AAny practi= cal suggestion (and/or references on the web) about how to build it?=0AAbou= t the ferrites, there are several sellers on eBay who offer a russian MU400= HH type. Would it be suitable for LF? Are there some recommended alternativ= es?=0A=A0=0ASorry for the (usual) long list of questions and thank you for = reading.=0A=A0=0ABest regards=0ADaniele=0A=0A=0A=0AFrom: James Moritz =0ATo: rsgb_lf_group@blacksheep.org=0ASent: Saturd= ay, August 20, 2011 12:07 PM=0ASubject: LF: Re: Ferrite wideband antennas?= =0A=0ADear Daniele, LF Group,=0A=0ARegarding bandwidth, the first thing to = note is that the same principles essentially apply to both air-cored loop a= nd ferrite rod cored loop antennas - the main difference is that air-cored = loops are wide and flat, but ferrite rods are long and thin ;-).=0A=0AAssum= ing you can make a preamp with a low enough noise level, the minimum usable= signal level "sensitivity" of a loop antenna depends on the ratio between = the induced signal level, and the level of thermal noise produced by the re= sistance of the loop windings, core losses, etc. So this sensitivity depend= s on the construction and size of the loop/rod, and in principle it does no= t matter if it is tuned for narrow-band resonance or loaded to produce wide= bandwidth, provided the tuning or loading arrangements do not introduce ad= ditional noise. But in practice, tuning/loading and preamplifiers will intr= oduce some additional noise.=0A=0AThe big advantage of a tuned loop is that= the resonant circuit can provide a high "passive gain". So Stefan's rod an= tenna probably produces an EMF in the nanovolt range for usable received si= gnal levels, but the high Q circuit it forms with a parallel capacitor incr= eases this voltage by more than 50dB The actual signal power level is not i= ncreased by the resonant circuit, but the much higher signal voltage is eas= ily handled by a simple preamplifier with insignificant additional noise in= troduced. The resonant circuit also has a very narrow bandwidth - this migh= t be an advantage for attenuating strong out-of-band signals, but is a draw= back if wideband reception is required, or remote tuning of the loop is nee= ded.=0A=0AIn many commercially available wideband loops, the loop is loaded= by a preamp with a very low input impedance. This provides a flat frequenc= y response, since the loop EMF rises in proportion to signal frequency, but= the signal current at the preamplifier input is maintained constant by the= reactance of the loop inductance, which=A0 also rises proportional to freq= uency. This flat response is very popular for measuring applications and wi= deband reception. But the preamp design is much more difficult, because the= input signal=A0 amplitude is effectively attenuated by the combination of = high loop reactance and low preamp input impedance. So careful preamp desig= n 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 high= er 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 loops= (~1m) seem to be neccessary to achieve a reasonable sensitivity. Of course= , if loop size is not an issue, one can simply increase the loop area=A0 to= produce a greater signal amplitude, and all that is needed is a large wire= loop terminated by a low impedance receiver input.=0A=0AIn my view, for co= mmunications reception purposes, creating a flat output voltage vs. field s= trength relationship for a wideband loop is not particularly useful - the b= ackground noise field strength decreases with frequency, so if you keep the= "natural" signal EMF-proportional-to-frequency response of a loop, the bac= kground noise at the receiver input remains fairly constant with frequency.= I have used 2x2m and 4 x 5m loop antennas where the loop inductance forms = the input inductor of a low-pass filter with cut-off frequency of about 550= kHz, in order to attenuate powerful broadcast signals. These give reasonabl= e results from VLF to 500kHz without any tuning adjustments.=0A=0ACheers, J= im Moritz=0A73 de M0BMU --0-771395587-1314641326=:93643 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
 
"all of view" meant = "all of you"...
 

From:= Daniele Tincani <danieletincani@yahoo.com>
To: "rsgb_lf_group@blacksheep.org" <= ;rsgb_lf_group@blacksheep.org>
S= ent: Monday, August 29, 2011 8:06 PM
Subject: Re: LF: Re: Ferrite wideband antennas?
=
 
Hello Jim, LF,
 
thanks to all of vie= w for feedbacks to my inquiry.
 
So my rough summary = is:
- small-size (e.g. ferrite cored) loops need tuning =3D high Q t= o provide a reasonable signal level.
- intermediate-size (e.g. 1m diameter or so) loops can be wide-b= and but require low-noise, very low-impedance pre-amps.
- bigger loops (e.g. > 2m diameter) can be wide-band even whe= n connected directly to a low-impedance receiver input (without a= pre-amplifier), may be through a broadband transformer to furtherly reduce= the load impedance as seen by the loop.
 
In general, loop size is more important for sensitivity than per= meability of core material and number of turns.
 
For practical reasons, for rx activity at home I'm building= a ~1m wide-band loop. The reference design for the amplifier is M0AYF's (d= espite it is not a very low-impedance pre-amp, I think).
 
Nevertheless, the discussion about ferrite-cored antennas here o= n the reflector is more and more pushing me to build my own "loopstick" and= experiment with it.
Could it be possible to tune a ferrite loop over a frequency ran= ge as wide as 100-500KHz? Or at least over the EU NDB band (say 300-500KHz)= ?
Any practical suggestion (and/or references on the web) about ho= w to build it?
About the ferrites, there are several sellers on eBay who offer = a russian MU400HH type. Would it be suitable for LF? Are there some recomme= nded alternatives?
 
Sorry for the (usual) long list of questions and thank you for r= eading.
 
Best regards
Daniele


From: James Moritz <james.moritz@btopenworld.com&g= t;
To: rsgb_lf_group@bla= cksheep.org
Sent: Saturd= ay, August 20, 2011 12:07 PM
Subjec= t: 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 c= ored loop antennas - the main difference is that air-cored loops are wide a= nd flat, but ferrite rods are long and thin ;-).

Assuming you can make= a preamp with a low enough noise level, the minimum usable signal level "s= ensitivity" of a loop antenna depends on the ratio between the induced sign= al level, and the level of thermal noise produced by the resistance of the = loop windings, core losses, etc. So this sensitivity depends on the constru= ction and size of the loop/rod, and in principle it does not matter if it i= s tuned for narrow-band resonance or loaded to produce wide bandwidth, prov= ided the tuning or loading arrangements do not introduce additional noise. = But in practice, tuning/loading and preamplifiers will introduce some addit= ional 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= produces an EMF in the nanovolt range for usable received signal levels, b= ut the high Q circuit it forms with a parallel capacitor increases this voltage by more than 50dB The actual signal power level is not increa= sed by the resonant circuit, but the much higher signal voltage is easily h= andled by a simple preamplifier with insignificant additional noise introdu= ced. The resonant circuit also 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.<= BR>
In many commercially available wideband loops, the loop is loaded by= a preamp with a very low input impedance. This provides a flat frequency r= esponse, since the loop EMF rises in proportion to signal frequency, but th= e signal current at the preamplifier input is maintained constant by the re= actance of the loop inductance, which  also rises proportional to freq= uency. This flat response is very popular for measuring applications and wi= deband reception. But the preamp design is much more difficult, because the input signal  amplitude is effectively attenuated by the = combination of high loop reactance and low preamp input impedance. So caref= ul preamp design is needed, to provide a low input impedance, very low nois= e voltage, and a low noise figure when fed from a highly mis-matched, relat= ively much higher source impedance. The "noiseless feedback" techniques suc= h as "Zwichenbasis" amplifiers mentioned by DF6NM or "Norton" feedback ampl= ifiers can be usefully used. But even with careful preamp design, relativel= y large loops (~1m) seem to be neccessary to achieve a reasonable sensitivi= ty. Of course, if loop size is not an issue, one can simply increase the lo= op area  to 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 particularly useful - the background noise field strength decreases with f= requency, 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







=
--0-771395587-1314641326=:93643--