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Wed, 15 Jun 2011 06:34:51 PDT X-Mailer: YahooMailRC/570 YahooMailWebService/0.8.111.304355 Date: Wed, 15 Jun 2011 06:34:51 -0700 (PDT) From: Daniele Tincani To: rsgb_lf_group@blacksheep.org MIME-Version: 1.0 DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: LF RX loop Content-Type: multipart/alternative; boundary="0-939539368-1308144891=:15259" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=FORGED_YAHOO_RCVD,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: 0:2:460846912:93952408 X-AOL-SCOLL-URL_COUNT: 0 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m279.1 ; domain : yahoo.com DKIM : pass x-aol-sid: 3039ac1d60574df8b5913056 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none --0-939539368-1308144891=:15259 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Apologies for re-sending this message, first time I selected the "Send" but= ton =0Aby mistake :-)=0AI wanted to add just a couple of general-interest r= eferences for loop antennas:=0Ahttp://www.frontiernet.net/~jadale/Loop.htm= =0Ahttp://groups.yahoo.com/group/loopantennas/=0ABest regards=0ADaniele=0A= =0A=A0=0A=0A________________________________=0AFrom: Daniele Tincani =0ATo: rsgb_lf_group@blacksheep.org=0ASent: Wed, June 1= 5, 2011 3:31:34 PM=0ASubject: Re: LF: LF RX loop=0A=0A=0AHello Stefan,=0A= =0Aas far as I know, you should avoid loading a resonant loop too much so I= would =0Asay that a preamp with an high input impedance is better (so no 5= 0 ohms load at =0Athe transformer output in my opinion).=0AAnother importan= t factor is balancing, which allows better rejection of common =0Amode curr= ents and deeper nulls.=0A=0A=0A=0A=0A________________________________=0AFro= m: Stefan Sch=E4fer =0ATo: rsgb_lf_group@bl= acksheep.org=0ASent: Wed, June 15, 2011 2:40:07 PM=0ASubject: LF: LF RX loo= p=0A=0ALF,=0A=0ASome questions about RX loops for LF.=0AYesterday i found a= shortcut between my loop ends. Thus i haven't found a =0Aresonance when va= rying the C. It is a single turn circular loop using copper =0Atube with 10= mm diameter (about 1m). I calculated the L with a formula of ON7YDs =0ALF i= nfo pages and found a C of about 470 nF which agreed very well. It was =0Ae= asily possible to resonate the loop with an induced signal by a smaller loo= p =0Aconnected to my VFO and measuring the C volatage with an oscilloscope.= I found =0Athe Q of the loop is just 8! Is this normal? Which Q do others = achieve, with a =0Asimilar antenna for 137 kHz?=0AI'm using PP capacitors w= hich should be well suitable (WIMA MKP10) =0Ahttp://www.wima.de/EN/WIMA_MKP= _10.pdf=0A=0AIt is fascinating to null out s signal, which i have done the = first time now. I =0Acan reduce the signal of DCF39 by 25 dB by turning the= loop. I assume there are =0Adifferent paths the signal comes from, this is= why i cannot eliminate it =0Acompletely, right?=0A=0AI used a high mu toro= id (ferroxube, blue material) to transform the primary side =0A(=3Dthe loop= ) to 50 Ohm. I have done this by varying the secondary turn number =0Auntil= i achieved a maximum voltage at a 50 Ohm load at a given input signal. The= =0Asecondary number is now about 25 turns. The resonance frequency is not = affected =0Aby the load at the output of the transformer.=0A=0ANow DCF39 ap= pears at up to 45 dB above noise in 3 Hz which. But it should be at =0Aleas= t 20 dB higher i think. Furthermore the background noise does not change at= =0Aall when i connect or disconnect the antenna. Thus i think it makes sen= se to =0Abuild a preamp. I found a suitable circuit on the pdf of Jim/M0BMU= s loop article =0Awhich looks well for me. Looking forward to this amp perf= ormance!=0A=0AIs it important to terminate the loops transformer output wit= h a 50 Ohm load in =0Athat case? On an oscilloscope i found that the level = of DCF39 is higher when =0Ahaving no R connected to the output but the wave= form looks much better / =0Acleaner!=0A=0AI'm optimistic to get much proper= reception of UK and PA and HB9 CW signals on =0A137 soon, when beeing outs= ide the city, steering the LF TX by the 70cm link :-)=0A=0AVy 73, Stefan/DK= 7FC --0-939539368-1308144891=:15259 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Apologies for re-sending this message, first time I selected the = "Send" button by mistake :-)
=0A
I wanted to add just a couple of = general-interest references for loop antennas:
=0A=0A=0A
Best r= egards
=0A
Daniele
=0A

 
=0A
=0A
=0A
=0AFrom: Daniele Tincani <danieletincani@yahoo.com>To: rsgb_lf_group@blackshe= ep.org
Sent: Wed, June 1= 5, 2011 3:31:34 PM
Subject:<= /B> Re: LF: LF RX loop

=0A=0A
=0A
Hello Stefan,
=0A
 
=0Aas far as I know, you should avoid loading a resonant loop too much so I= would say that a preamp with an high input impedance is better (so no 50 o= hms load at the transformer output in my opinion).
=0A
Another imp= ortant factor is balancing, which allows better rejection of common mode cu= rrents and deeper nulls.
=0A
 
=0A

=0A
=0A
=0AFrom: Stefan Sch=E4fer <schaefer@iup.uni-heidelberg.de>
To: rsgb_lf_group@blacksheep.org<= BR>Sent: Wed, June 15, 2011= 2:40:07 PM
Subject: LF:= LF RX loop

LF,

Some questions about RX loops for LF.<= BR>Yesterday i found a shortcut between my loop ends. Thus i haven't found = a resonance when varying the C. It is a single turn circular loop using cop= per tube with 10mm diameter (about 1m). I calculated the L with a formula o= f ON7YDs LF info pages and found a C of about 470 nF which agreed very well= . It was easily possible to resonate the loop with an induced signal by a s= maller loop connected to my VFO and measuring the C volatage with an oscill= oscope. I found the Q of the loop is just 8! Is this normal? Which Q do oth= ers achieve, with a similar antenna for 137 kHz?
I'm using PP capacitors which should be well suita= ble (WIMA MKP10) http://www.wima.de/EN/WIMA_MKP_10.pdf

It is fascina= ting to null out s signal, which i have done the first time now. I can redu= ce the signal of DCF39 by 25 dB by turning the loop. I assume there are dif= ferent paths the signal comes from, this is why i cannot eliminate it compl= etely, right?

I used a high mu toroid (ferroxube, blue material) to = transform the primary side (=3Dthe loop) to 50 Ohm. I have done this by var= ying the secondary turn number until i achieved a maximum voltage at a 50 O= hm load at a given input signal. The secondary number is now about 25 turns= . The resonance frequency is not affected by the load at the output of the = transformer.

Now DCF39 appears at up to 45 dB above noise in 3 Hz wh= ich. But it should be at least 20 dB higher i think. Furthermore the backgr= ound noise does not change at all when i connect or disconnect the antenna. Thus i think it makes sense to build a preamp. I found a suitable= circuit on the pdf of Jim/M0BMUs loop article which looks well for me. Loo= king forward to this amp performance!

Is it important to terminate t= he loops transformer output with a 50 Ohm load in that case? On an oscillos= cope i found that the level of DCF39 is higher when having no R connected t= o the output but the waveform looks much better / cleaner!

I'm optim= istic to get much proper reception of UK and PA and HB9 CW signals on 137 s= oon, when beeing outside the city, steering the LF TX by the 70cm link :-)<= BR>
Vy 73, Stefan/DK7FC

=0A
--0-939539368-1308144891=:15259--