Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=0.0 required=5.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 X-Spam-DCC: : mailn 1480; Body=3 Fuz1=3 Fuz2=3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by lipkowski.org (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id v756xUlf012364 for ; Sat, 5 Aug 2017 08:59:31 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ddt04-0001Ps-HA for rs_out_1@blacksheep.org; Sat, 05 Aug 2017 07:55:52 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ddt01-0001Pf-F2 for rsgb_lf_group@blacksheep.org; Sat, 05 Aug 2017 07:55:49 +0100 Received: from mout3.freenet.de ([2001:748:100:40::2:5]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1ddszy-0006iQ-O7 for rsgb_lf_group@blacksheep.org; Sat, 05 Aug 2017 07:55:48 +0100 Received: from [195.4.92.141] (helo=mjail1.freenet.de) by mout3.freenet.de with esmtpa (ID dl4yhf@freenet.de) (port 25) (Exim 4.89 #1) id 1ddszt-0007fJ-JU for rsgb_lf_group@blacksheep.org; Sat, 05 Aug 2017 08:55:41 +0200 Received: from localhost ([::1]:35476 helo=mjail1.freenet.de) by mjail1.freenet.de with esmtpa (ID dl4yhf@freenet.de) (Exim 4.85 #1) id 1ddszt-0000v1-Fg for rsgb_lf_group@blacksheep.org; Sat, 05 Aug 2017 08:55:41 +0200 Received: from mx6.freenet.de ([195.4.92.16]:43942) by mjail1.freenet.de with esmtpa (ID dl4yhf@freenet.de) (Exim 4.85 #1) id 1ddsxO-0000NY-8I for rsgb_lf_group@blacksheep.org; Sat, 05 Aug 2017 08:53:06 +0200 Received: from x4d08385d.dyn.telefonica.de ([77.8.56.93]:64502 helo=[192.168.178.26]) by mx6.freenet.de with esmtpsa (ID dl4yhf@freenet.de) (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (port 587) (Exim 4.89 #1) id 1ddsxO-0004yk-1g for rsgb_lf_group@blacksheep.org; Sat, 05 Aug 2017 08:53:06 +0200 To: rsgb_lf_group@blacksheep.org References: <0883B95D3F4D417F975C59A900E1A838@gnat> <3D9A092BFA65418DBEE13188A4C58580@gnat> <92ce2c22-a887-bb8f-6bc2-6f03b51899d6@t-online.de> From: =?UTF-8?Q?Wolfgang_B=c3=bcscher?= Message-ID: Date: Sat, 5 Aug 2017 08:53:00 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <92ce2c22-a887-bb8f-6bc2-6f03b51899d6@t-online.de> X-Originated-At: 77.8.56.93!64502 X-Scan-Signature: 4e3b1488273adbbe9757d6bdd5adf219 Subject: Re: LF: G4HUP aerial current meter/ hazards Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit 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-Scanned-By: MIMEDefang 2.75 Status: RO X-Status: X-Keywords: X-UID: 12329 ... and never forget to wind a 'secondary' over the current transformer, always terminated with low resistance. Otherwise you will quickly saturate it, which is something that NO current transformer will tolerate at moderate levels ! Running a current transformer with an "open secondary" (or non-existing secondary) should be avoided. Cheers, Wolf . Am 05.08.2017 um 07:38 schrieb Dr. Wolf Ostwald: > good morning ! > a current transformer with ferrites of unknown origin and virtues is a > very risky thing. > As these cores are widely available on swapmeets its a lure to use them. > But they can be tested. I blew a few of them by just putting them on > with a single primary turn and with power less than a hundred watts > they got hot and broke. > The losses can be extremely high. > It does not help to measure their magnetic constant. As that has not > much to do with frequency dependent losses. > a way to find out is to use a 50 ohm load and measure the RF voltage > across the terminals. Then u just put the toroid over the "hot" side > of the resistor terminals. > If the measured RF voltage drops heavily, the core is useless. You > dont want it to block, u want to derive some RF for measuring purposes. > The above core would go into pieces and additionally as it poses a > high inductance to ur feedline, the amplifier stage may go south, > depending on the safety factor involved with ur construction . > > 73 de wolf df2py >