Return-Path: Received: from mtain-ma03.r1000.mx.aol.com (mtain-ma03.r1000.mx.aol.com [172.29.96.11]) by air-dc10.mail.aol.com (v129.4) with ESMTP id MAILINDC103-86564d330d26b3; Sun, 16 Jan 2011 10:22:14 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-ma03.r1000.mx.aol.com (Internet Inbound) with ESMTP id DA63C38000081; Sun, 16 Jan 2011 10:22:12 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PeUPg-0006w2-Gi for rs_out_1@blacksheep.org; Sun, 16 Jan 2011 15:21:04 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PeUPf-0006vt-OY for rsgb_lf_group@blacksheep.org; Sun, 16 Jan 2011 15:21:03 +0000 Received: from mail-iw0-f171.google.com ([209.85.214.171]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PeUPd-0002jw-3g for rsgb_lf_group@blacksheep.org; Sun, 16 Jan 2011 15:21:03 +0000 Received: by iwn2 with SMTP id 2so4116151iwn.16 for ; Sun, 16 Jan 2011 07:20:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:date:message-id:subject:from:to :content-type; bh=U/A0IrGItTGpd2bGVgQ2ggRmbqxrHBtOLR/GYuTXrV0=; b=ZgbjsVPUfx0uPYn7Ue/bATh6uZnGeRcjlYSChgoklU802HwvIG1VCqELlFR14TzNHS OTfUVidzpRD+CECWJIdJxh1ME8y+jCKEukBih86CwcKO+IIIN6KE9bX/yKaixwjHN9Hl 9W/VC7O3PMaVhDtXMCxO8XaCQ8N3wpnVh6ai0= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=dSO2AekencRURrbzQLK01WND18SpmpvHXC4xTKzCM1c73Dh/f+iXDGe2qCrDYbR1UN FFBgs8gaFoggEg7fo/6a5NRarJ3Mrvxs+SUucDK9vbc9lx8Xejn3IBswCEHFhxSjZY5z kw3ShjmsRlEJphAhI3K3Hq1YU0YFiqJ2P80Xg= MIME-Version: 1.0 Received: by 10.42.5.201 with SMTP id 9mr3263201icx.300.1295191259221; Sun, 16 Jan 2011 07:20:59 -0800 (PST) Received: by 10.42.241.133 with HTTP; Sun, 16 Jan 2011 07:20:59 -0800 (PST) Date: Sun, 16 Jan 2011 15:20:59 +0000 Message-ID: From: Roger Lapthorn To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.3 (/) X-Spam-Report: autolearn=disabled,HTML_IMAGE_RATIO_02=0.192,HTML_MESSAGE=0.001,HTML_TAG_EXIST_TBODY=0.126 Subject: LF: Capacitance switch box design - what is the simplest? Content-Type: multipart/alternative; boundary=005045014712ec0e5d0499f836e2 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.3 required=5.0 tests=HTML_50_60,HTML_MESSAGE, HTML_TAG_EXISTS_TBODY 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-AUTHENTICATION: mail_rly_antispam_dkim-m023.1 ; domain : gmail.com DKIM : fail x-aol-sid: 3039ac1d600b4d330d243c0d X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) --005045014712ec0e5d0499f836e2 Content-Type: text/plain; charset=ISO-8859-1 These may be stupid questions (indeed I may have asked them already months ago) but here goes.... To match my simple loop antenna on TX on 136 and 500kHz I've been using an old laboratory capacitance decade box. At the very low powers I have been using, the voltage ratings of the capacitors within the box have been adequate and results predictable and repeatable. However, as I increase the RF power I'm beginning to see the capacitors suffering and values change over a minute or so because the components are being used beyond their (voltage or heat I assume) ratings. With a hi-Q loop I guess the voltage across the capacitance can be very many times larger than that at 50 ohms. So, I need *to build a capacitance selection box with values from around 0-30nF with sufficient resolution to fine tune a hi-Q loop*. I will need the capacitors to be rated sufficiently high voltage to cope with any power level I am likely to put into the loop antenna (almost certainly never more than 20-30W though). My questions are these: (a) what is the best *choice of capacitors* - type, voltage working, pulse behaviour, accuracy, price? (b) what is the *simplest arrangement* to give me the adjustment accuracy and range I need with the fewest parts and fewest switches? Any advice would be appreciated. 73s Roger G3XBM -- g3xbm-qrp.blogspot.com/ www.g3xbm.co.uk www.youtube.com/user/g3xbm G3XBM GQRP 1678 ISWL G11088 <#> <#> <#> <#> --005045014712ec0e5d0499f836e2 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable These may be stupid questions (indeed I may have asked them already months= ago) but here goes....

To match my simple loop antenna on TX on 13= 6 and 500kHz I've been using an old laboratory capacitance decade box.= At the very low powers I have been using, the voltage ratings of the capa= citors within the box have been adequate and results predictable and repea= table. However, as I increase the RF power I'm beginning to see the ca= pacitors suffering and values change over a minute or so because the compo= nents are being used beyond their (voltage or heat I assume) ratings. With= a hi-Q loop I guess the voltage across the capacitance can be very many= times larger than that at 50 ohms.

So, I need to build a capacitance selection box with values from ar= ound 0-30nF with sufficient resolution to fine tune a hi-Q loop. I wil= l need the capacitors to be rated sufficiently high voltage to cope with= any power level I am likely to put into the loop antenna (almost certainl= y never more than 20-30W though).

My questions are these:

(a)= what is the best choice of capacitors - type, voltage worki= ng, pulse behaviour, accuracy, price?
(b) what is the simplest ar= rangement to give me the adjustment accuracy and range I need with= the fewest parts and fewest switches?

Any advice would be appreciated.

73s
Roger G3XBM
--=
g3xbm-qr= p.blogspot.com/
www.g3xbm.co.uk
www.youtub= e.com/user/g3xbm
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--005045014712ec0e5d0499f836e2--