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RozmKDJcxrLzHjPXC9fgfwRoHGuauYDRcqzgScrVk46IHhglm7JlegzPee92 087izwhdndQEy1VD4xVUDQkPVLo22LzbfX96OVCkJP7pr.NFA37vqygv7AKC z7UCsHqON.kEw4T97QHddzIpyHB4xGBfdx4DkyX2mOB0KQwhlnszc304DCT8 s12T3vCyIqT8zDXfYt9Utv1ZgoycGn5zn9BrYLfC9AYEb1vafrniOjUN_F.D k77GbLuQK7T5vREplrguddQBsraGOR4qBZ7yWx1jzP0t1.fBE.Wn7FHM4L2h RrPXUbSgwpjfE6IBw8p4_BU9syWNeD.k8cAYo.t2X5FFEqh2h Received: from [151.99.187.181] by web111910.mail.gq1.yahoo.com via HTTP; Mon, 29 Aug 2011 11:06:23 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> Message-ID: <1314641183.5605.YahooMailNeo@web111910.mail.gq1.yahoo.com> Date: Mon, 29 Aug 2011 11:06:23 -0700 (PDT) From: Daniele Tincani To: "rsgb_lf_group@blacksheep.org" In-Reply-To: <1314394178.5030.YahooMailNeo@web111905.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="0-1758706842-1314641183=:5605" 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: 0:2:484930112:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d280.1 ; domain : yahoo.com DKIM : fail x-aol-sid: 3039ac1d600d4e5bd55f085b X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none --0-1758706842-1314641183=:5605 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable =A0=0AHello Jim, LF,=0A=A0=0Athanks to all of view for feedbacks to my inqu= iry.=0A=A0So my rough summary is:=0A- small-size (e.g. ferrite cored) loops= need tuning =3D high Q to provide a reasonable signal level.=0A- intermedi= ate-size (e.g. 1m diameter or so) loops can be wide-band but require=A0low-= noise, very low-impedance pre-amps.=0A- bigger loops (e.g. > 2m diameter) c= an be wide-band even when connected directly=A0to a low-impedance receiver = input=A0(without a pre-amplifier), may be through a broadband transformer t= o furtherly reduce the load impedance as seen by the loop.=0A=A0=0AIn gener= al, loop size is more important for sensitivity than permeability of core m= aterial=A0and number of turns.=0A=A0=0AFor practical reasons,=A0for rx acti= vity at home I'm building a ~1m wide-band loop. The reference design for th= e amplifier is M0AYF's (despite it is not a very low-impedance pre-amp, I t= hink).=0A=A0=0ANevertheless, the discussion about ferrite-cored antennas he= re on the reflector is more and more pushing me to build my own "loopstick"= and experiment with it.=0ACould 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 practical suggestion (and/or references on the web)= about how to build it?=0AAbout the ferrites, there are several sellers on = eBay who offer a russian MU400HH type. Would it be suitable for LF? Are the= re some recommended alternatives?=0A=A0=0ASorry for the (usual) long list o= f questions and thank you for reading.=0A=A0=0ABest regards=0ADaniele=0A=0A= =0A=0AFrom: James Moritz =0ATo: rsgb_lf_group= @blacksheep.org=0ASent: Saturday, August 20, 2011 12:07 PM=0ASubject: LF: R= e: Ferrite wideband antennas?=0A=0ADear Daniele, LF Group,=0A=0ARegarding b= andwidth, the first thing to note is that the same principles essentially a= pply to both air-cored loop and 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=0AAssuming you can make a preamp with a low enough no= ise level, the minimum usable signal level "sensitivity" of a loop antenna = depends on the ratio between the induced signal level, and the level of the= rmal noise produced by the resistance of the loop windings, core losses, et= c. So this sensitivity depends on the construction and size of the loop/rod= , and in principle it does not matter if it is tuned for narrow-band resona= nce or loaded to produce wide bandwidth, provided the tuning or loading arr= angements do not introduce additional noise. But in practice, tuning/loadin= g and preamplifiers will introduce some additional noise.=0A=0AThe big adva= ntage of a tuned loop is that the resonant circuit can provide a high "pass= ive gain". So Stefan's rod antenna probably produces an EMF in the nanovolt= range for usable received signal levels, but the high Q circuit it forms w= ith a parallel capacitor increases this voltage by more than 50dB The actua= l signal power level is not increased by the resonant circuit, but the much= higher signal voltage is easily handled by a simple preamplifier with insi= gnificant additional noise introduced. The resonant circuit also has a very= narrow bandwidth - this might be an advantage for attenuating strong out-o= f-band signals, but is a drawback if wideband reception is required, or rem= ote tuning of the loop is needed.=0A=0AIn many commercially available wideb= and 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 propor= tion to signal frequency, but the signal current at the preamplifier input = is maintained constant by the reactance of the loop inductance, which=A0 al= so rises proportional to frequency. This flat response is very popular for = measuring applications and wideband reception. But the preamp design is muc= h more difficult, because the input signal=A0 amplitude is effectively atte= nuated by the combination of high loop reactance and low preamp input imped= ance. So careful preamp design 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 higher source impedance. The "noiseless feedback" = techniques such as "Zwichenbasis" 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 --0-1758706842-1314641183=:5605 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
 
Hello Jim, LF,
 
thanks to all of vie= w for feedbacks to my inquiry.
 
<= SPAN style=3D"RIGHT: auto">
So my rough summary = is:
- small-size (e.g. f= errite cored) loops need tuning =3D high Q to provide a reasonable signal l= evel.
- intermediate-size = (e.g. 1m diameter or so) loops can be wide-band but require low-noise,= very low-impedance pre-amps.
- bigger loops (e.g.= > 2m diameter) can be wide-band even when 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 siz= e is more important for sensitivity than permeability of core material = ;and number of turns.
 
For practical reason= s, for rx activity at home I'm building a ~1m wide-band loop. The refe= rence design for the amplifier is M0AYF's (despite it is not a very low-imp= edance pre-amp, I think).
 
Nevertheless, the di= scussion about ferrite-cored antennas here on the reflector is more and mor= e pushing me to build my own "loopstick" and experiment with it.
Could 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)?
Any practical sugges= tion (and/or references on the web) about how to build it?
About the ferrites, = there are several sellers on eBay who offer a russian MU400HH type. Would i= t be suitable for LF? Are there some recommended alternatives?
 
Sorry for the (usual= ) long list of questions and thank you for reading.
 
Best regards<= /DIV>
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





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