Return-Path: Received: from mtain-me09.r1000.mx.aol.com (mtain-me09.r1000.mx.aol.com [172.29.96.145]) by air-me08.mail.aol.com (v129.4) with ESMTP id MAILINME083-8bbe4d331c28240; Sun, 16 Jan 2011 11:26:16 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-me09.r1000.mx.aol.com (Internet Inbound) with ESMTP id 2ADAC380000AF; Sun, 16 Jan 2011 11:26:14 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PeVPc-0007Uh-JK for rs_out_1@blacksheep.org; Sun, 16 Jan 2011 16:25:04 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PeVPb-0007UY-Lq for rsgb_lf_group@blacksheep.org; Sun, 16 Jan 2011 16:25:03 +0000 Received: from mail-iy0-f171.google.com ([209.85.210.171]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PeVPZ-000362-6U for rsgb_lf_group@blacksheep.org; Sun, 16 Jan 2011 16:25:03 +0000 Received: by iyj21 with SMTP id 21so4187131iyj.16 for ; Sun, 16 Jan 2011 08:24:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type; bh=l44klKqe9KUslD2/dkPwHo1lbx1GR55Jr2AYA6ldE1U=; b=jox3vo1hoeGd+ceJqblmDVKYGOYJIg9DRt0AqYL0Y8et3FyLBUQhzWywZTL8uJTqXz MRGZa0giQR0n7uYIoUpeBkgAxeJgvRBKWKJKVT5syZBvx4DcGB/JndLdlg6eNJVMDAzM DI8RVbmKKjCiC6e/y6gpDxZh5rSEQ51sR1/uY= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=ZxRIkAeVxaczDqhL5rrzBKCT+iTsUkhf4/oQGRR7KhvMkWjvaNZm70CaBiGNDBM59+ wKbbVCJMaXeUpqjPkGyo4V2nI/Py8OCC00LG2d2/tuweWUglEjN03fFW7OpSJsTFRmpG i2hLkosDUsXzwNaXI+lBG266j/+FMuNxnpKFM= MIME-Version: 1.0 Received: by 10.42.177.69 with SMTP id bh5mr3302773icb.367.1295195094600; Sun, 16 Jan 2011 08:24:54 -0800 (PST) Received: by 10.42.241.133 with HTTP; Sun, 16 Jan 2011 08:24:54 -0800 (PST) In-Reply-To: <006901cbb595$e50b51f0$4001a8c0@lark> References: <532F7D4648B74CCF825F0D0E596655AF@home2361108df7> <006901cbb595$e50b51f0$4001a8c0@lark> Date: Sun, 16 Jan 2011 16:24:54 +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: Re: LF: Re: Re: Capacitance switch box design - what is the simplest? Content-Type: multipart/alternative; boundary=90e6ba6e8cae874c9a0499f91b7f 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-m234.1 ; domain : gmail.com DKIM : pass x-aol-sid: 3039ac1d60914d331c2665f9 X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) --90e6ba6e8cae874c9a0499f91b7f Content-Type: text/plain; charset=ISO-8859-1 Thanks for the *FAST* response to my cap switch box question: I got 3 within 20 minutes on and off the list. It's good to see people here are so helpful, even when the question may seem a trivial one. I'll make an order for a bunch of the recommended caps tonight and some thicker wire for the loop. The loop antenna does seem to be a good solution for me as I can use the same arrangement on a number of bands. With my QRP power levels I can also tune it indoors - I think. 73s Roger G3XBM On 16 January 2011 15:56, Alan Melia wrote: > Or "5" caps 1,2,4,8,16...... really 5 switches becasue you may need to > parallel caps to meet these values. I suggest the high voltage pulse-rated > caps that we (Andy et al) were recently talking about using in high power > PA > tuning. I use WIMA PHE 428 series, which I think I got from RS (Farnell do > a > RIFA equivalent) I guess they were about 75p each a few years ago. Very > high > voltages are generated across the loop when you apply power, so its a shame > to subject good quality caps in a sub box that that kind of treatment (yup > I > am a test equipment hugger :-)) ) > > You will probably want a smaller "granularity" than 1nF, so you may need to > include a 470PF and a 500pF wide spaced variable in the box, especially if > as you quote it is a high Q loop. > > Alan G3NYK > > > ----- Original Message ----- > From: "Martin Evans" > To: > Sent: Sunday, January 16, 2011 3:32 PM > Subject: LF: Re: Capacitance switch box design - what is the simplest? > > > > > 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 > > > > > > Well, to do 1nF to 30nF in 1nF steps, you need six caps and six switches > - > > > > 1, 2, 2, 5, 10, 10nf caps > > > > all in parallel, with a (toggle?) switch in series with each capacitor. > > > > Martin GW3UCJ. > > > > > > > > > > > -- g3xbm-qrp.blogspot.com/ www.g3xbm.co.uk www.youtube.com/user/g3xbm G3XBM GQRP 1678 ISWL G11088 <#> <#> <#> <#> --90e6ba6e8cae874c9a0499f91b7f Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Thanks for the FAST response to my cap switch box question: I got= 3 within 20 minutes on and off the list.=A0 It's good to see people= here are so helpful, even when the question may seem a trivial one.
I'll make an order for a bunch of the recommended caps tonight and= some thicker wire for the loop. The loop antenna does seem to be a good= solution for me as I can use the same arrangement on a number of bands.= With my QRP power levels I can also tune it indoors - I think.

73s
Roger G3XBM

On 16 January 201= 1 15:56, Alan Melia <alan.melia@btinternet.com> wrote:
Or "5" caps 1,2,4,8,16...... really 5 switches becasue you may= need to
parallel caps to meet these values. I suggest the high voltage pulse-rated=
caps that we (Andy et al) were recently talking about using in high power= PA
tuning. I use WIMA PHE 428 series, which I think I got from RS (Farnell do= a
RIFA equivalent) I guess they were about 75p each a few years ago. Very hi= gh
voltages are generated across the loop when you apply power, so its a sham= e
to subject good quality caps in a sub box that that kind of treatment (yup= I
am a test equipment hugger :-)) =A0)

You will probably want a smaller "granularity" than 1nF, so you= may need to
include a 470PF and a 500pF wide spaced variable in the box, especially if=
as you quote it is a high Q loop.

Alan G3NYK


----- Original Message -----
From: "Martin Evans" <books@mollies.freeserve.co.uk>
To: <rsgb_lf_group@blac= ksheep.org>
Sent: Sunday, January 16, 2011 3:32 PM
Subject: LF: Re: Capacitance switch box design - what is the simplest?


> > 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 fro= m 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 an= y 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 work= ing,
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
>
>
> Well, to do 1nF to 30nF in 1nF steps, you need six caps and six switc= hes -
>
> 1, 2, 2, 5, 10, 10nf caps
>
> all in parallel, =A0with a (toggle?) switch in series with each capac= itor.
>
> Martin =A0GW3UCJ.
>
>
>
>





--
g3xbm-qrp.blogspot.com/
www.g3xbm.co.uk
= www.youtub= e.com/user/g3xbm
G3XBM=A0=A0 GQRP 1678= =A0=A0=A0 ISWL G11088
= 3D""
=20 =20
=A0 =A0
=20
=A0
3D"" =A0 3D"" =A0 =A0 =A0
=20
=A0
=A0
=20 =20 =20
=20 =20 =20 = =20
= =20
=20
=20
--90e6ba6e8cae874c9a0499f91b7f--