Received: from post.thorcom.com (post.thorcom.com [195.171.43.25])
	by mtain-dl03.r1000.mx.aol.com (Internet Inbound) with ESMTP id 492AF380000B4;
	Thu, 16 Jun 2011 17:17:44 -0400 (EDT)
Received: from majordom by post.thorcom.com with local (Exim 4.14)
	id 1QXJuo-0005ls-Sr
	for rs_out_1@blacksheep.org; Thu, 16 Jun 2011 22:15:50 +0100
Received: from [195.171.43.32] (helo=relay1.thorcom.net)
	by post.thorcom.com with esmtp (Exim 4.14)
	id 1QXJuo-0005lj-D3
	for rsgb_lf_group@blacksheep.org; Thu, 16 Jun 2011 22:15:50 +0100
Received: from mailout-de.gmx.net ([213.165.64.22])
	by relay1.thorcom.net with smtp (Exim 4.63)
	(envelope-from <cpaul@gmx.net>)
	id 1QXJum-00078B-3e
	for rsgb_lf_group@blacksheep.org; Thu, 16 Jun 2011 22:15:50 +0100
Received: (qmail invoked by alias); 16 Jun 2011 21:15:41 -0000
Received: from p4FD0D712.dip.t-dialin.net (EHLO Clemens04) [79.208.215.18]
  by mail.gmx.net (mp010) with SMTP; 16 Jun 2011 23:15:41 +0200
X-Authenticated: #17214767
X-Provags-ID: V01U2FsdGVkX18zODZDQOYzHKKIjQNPWFt42xr1/vVEl5lM5Ya9NC
	/Yf3tDRrHJXQmW
Message-ID: <01a101cc2c6a$8c31a100$1502a8c0@Clemens04>
From: "Clemens  Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
References: <4DF8A827.9070106@iup.uni-heidelberg.de>
Date: Thu, 16 Jun 2011 23:15:32 +0200
MIME-Version: 1.0
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2900.3664
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3664
X-Y-GMX-Trusted: 0
X-Spam-Score: 0.0 (/)
X-Spam-Report: autolearn=disabled,none
Subject: LF: Re: LF RX loop
Content-Type: text/plain;
	format=flowed;
	charset="iso-8859-15";
	reply-type=response
Content-Transfer-Encoding: 8bit
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=none 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: 0:2:435623488:93952408  
X-AOL-SCOLL-URL_COUNT: 0  
x-aol-sid: 3039ac1d4ad14dfa72f87e97
X-AOL-IP: 195.171.43.25
X-AOL-SPF: domain : blacksheep.org SPF : none


Stefan,

just to be sure how you have measured Q.
If you are feeding the loop with a 50 Ohm source and want
to measure the unloaded Q of the loop as per the formula
Q = f0/B you would have to look where the SWR rises to 2.618
(not 5.8).
This translates to a voltage drop at the terminals from e.g. 224mV to 200mV
(-0.969dB) for a 0dBm power source (i.e. power reduction is  20%, not 50%).

73
Clemens
DL4RAJ
.

----- Original Message ----- 
From: "Stefan Schäfer" <schaefer@iup.uni-heidelberg.de>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, June 15, 2011 2:40 PM
Subject: LF: LF RX loop


> LF,
>
> Some questions about RX loops for LF.
> 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 copper 
> tube with 10mm diameter (about 1m). I calculated the L with a formula of 
> 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 smaller 
> loop connected to my VFO and measuring the C volatage with an oscilloscope. I 
> found the Q of the loop is just 8! Is this normal? Which Q do others achieve, 
> with a similar antenna for 137 kHz?
> I'm using PP capacitors which should be well suitable (WIMA MKP10) 
> http://www.wima.de/EN/WIMA_MKP_10.pdf
>
> It is fascinating to null out s signal, which i have done the first time now. 
> I can reduce the signal of DCF39 by 25 dB by turning the loop. I assume there 
> are different paths the signal comes from, this is why i cannot eliminate it 
> completely, right?
>
> I used a high mu toroid (ferroxube, blue material) to transform the primary 
> side (=the loop) to 50 Ohm. I have done this by varying the secondary turn 
> number until i achieved a maximum voltage at a 50 Ohm 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 which. But it should be 
> at least 20 dB higher i think. Furthermore the background 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. Looking forward to this amp performance!
>
> Is it important to terminate the loops transformer output with a 50 Ohm load 
> in that case? On an oscilloscope i found that the level of DCF39 is higher 
> when having no R connected to the output but the waveform looks much better / 
> cleaner!
>
> I'm optimistic to get much proper reception of UK and PA and HB9 CW signals on 
> 137 soon, when beeing outside the city, steering the LF TX by the 70cm link 
> :-)
>
> Vy 73, Stefan/DK7FC
>
>
>
> -----
> eMail ist virenfrei.
> Von AVG überprüft - www.avg.de
> Version: 10.0.1382 / Virendatenbank: 1513/3705 - Ausgabedatum: 15.06.2011