Return-Path: Received: from mtain-me05.r1000.mx.aol.com (mtain-me05.r1000.mx.aol.com [172.29.96.141]) by air-da07.mail.aol.com (v129.4) with ESMTP id MAILINDA074-86674d3329283ab; Sun, 16 Jan 2011 12:21:44 -0500 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-me05.r1000.mx.aol.com (Internet Inbound) with ESMTP id BC552380000B9; Sun, 16 Jan 2011 12:21:42 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PeWHm-0008EU-6q for rs_out_1@blacksheep.org; Sun, 16 Jan 2011 17:21:02 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PeWHl-0008EJ-G6 for rsgb_lf_group@blacksheep.org; Sun, 16 Jan 2011 17:21:01 +0000 Received: from blu0-omc1-s26.blu0.hotmail.com ([65.55.116.37]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PeWHk-0003YP-4y for rsgb_lf_group@blacksheep.org; Sun, 16 Jan 2011 17:21:01 +0000 Received: from BLU146-W37 ([65.55.116.7]) by blu0-omc1-s26.blu0.hotmail.com with Microsoft SMTPSVC(6.0.3790.4675); Sun, 16 Jan 2011 09:20:52 -0800 Message-ID: X-Originating-IP: [24.116.236.64] From: Laurence KL7UK To: Date: Sun, 16 Jan 2011 08:20:52 -0900 Importance: Normal In-Reply-To: References: ,<532F7D4648B74CCF825F0D0E596655AF@home2361108df7>,<006901cbb595$e50b51f0$4001a8c0@lark>, MIME-Version: 1.0 X-OriginalArrivalTime: 16 Jan 2011 17:20:52.0587 (UTC) FILETIME=[BA0B83B0:01CBB5A1] X-Spam-Score: 0.1 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,HTML_TAG_EXIST_TBODY=0.126 Content-Type: multipart/alternative; boundary="_a9f2e642-c7a4-4a8f-a5c9-7cbe888bf492_" Subject: RE: LF: Re: Re: Capacitance switch box design - what is the simplest? X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.2 required=5.0 tests=FORGED_HOTMAIL_RCVD,HTML_70_80, 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-sid: 3039ac1d608d4d332926017e X-AOL-IP: 195.171.43.25 X-Mailer: Unknown (No Version) --_a9f2e642-c7a4-4a8f-a5c9-7cbe888bf492_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable For those that have word.doc I commend reading Bill Ashlocks' 2 part serie= s on Loops and conductor sizing etc via Mike WE0H's link http://www.we0h.us/Amateur_Radio_stuff/Transmitting-Loops/Bill-Ashlock-doc= uments/ =20 ...must get a .doc reader on this old monster of a PC.. =20 Laurence KL7 UK / 5 =20 Date: Sun, 16 Jan 2011 16:24:54 +0000 From: rogerlapthorn@gmail.com To: rsgb_lf_group@blacksheep.org Subject: Re: LF: Re: Re: Capacitance switch box design - what is the simpl= est? 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 help= ful, even when the question may seem a trivial one. I'll make an order for a bunch of the recommended caps tonight and some th= icker 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 QR= P 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 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 :-)) ) 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 arou= nd > > 0-30nF with sufficient resolution to fine tune a hi-Q loop*. I will ne= ed > > the > > capacitors to be rated sufficiently high voltage to cope with any powe= r > > 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. > > > > --=20 g3xbm-qrp.blogspot.com/ www.g3xbm.co.uk www.youtube.com/user/g3xbm G3XBM GQRP 1678 ISWL G11088 =20 =20 =20 =20 =20 =20 =20 =20 =20 =20 =20 =20 =20 =3D --_a9f2e642-c7a4-4a8f-a5c9-7cbe888bf492_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable For those that have word.doc I commend reading Bill Ashlocks' 2 part serie= s on Loops and conductor sizing etc via Mike WE0H's link
http://www.we0h.us/Amateur_Radio_stuff/Transmitting-Lo= ops/Bill-Ashlock-documents/
 
...must get a .doc reader on this old monster of a PC..
 
Laurence KL7 UK / 5

 
Date: Sun, 16 Jan 2011 16:24:54 +0000
From: rogerlapthorn@gmail.com
= To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: Re: Capacitance= switch box design - what is the simplest?

Thanks for the FAST response to my cap switch box question: I got 3 within 20 minutes on an= d off the list.  It's good to see people here are so helpful, even wh= en the question may seem a trivial one.

I'll make an order for a bu= nch of the recommended caps tonight and some thicker wire for the loop. Th= e loop antenna does seem to be a good solution for me as I can use the sam= e arrangement on a number of bands. With my QRP power levels I can also tu= ne it indoors - I think.

73s
Roger G3XBM

On 16 January 2011 15:56, Alan Melia <alan.melia@btinter= net.com> wrote:
Or "5" caps= 1,2,4,8,16...... really 5 switches becasue you may need to
parallel ca= ps to meet these values. I suggest the high voltage pulse-rated
caps th= at we (Andy et al) were recently talking about using in high power PA
t= uning. 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 kin= d of treatment (yup I
am a test equipment hugger :-))  )

Yo= u will probably want a smaller "granularity" than 1nF, so you may need to<= BR>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@blacksh= eep.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 sel= ection box with values from around
> > 0-30nF with sufficient res= olution to fine tune a hi-Q loop*. I will need
> > the
> &g= t; capacitors to be rated sufficiently high voltage to cope with any power=
> > level I am likely to put into the loop antenna (almost certa= inly never
> > more
> > than 20-30W though).
> >= ;
> > My questions are these:
> >
> > (a) what= is the best *choice of capacitors* - type, voltage working,
pulse
&= gt; > behaviour, accuracy, price?
> > (b) what is the *simples= t arrangement* to give me the adjustment
accuracy
> > and rang= e I need with the fewest parts and fewest switches?
> >
>= > Any advice would be appreciated.
> >
> > 73s
&g= t; > 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?) swi= tch 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
3D""
   
 
3D""   3D""      
 
 
=
=
<= /TD>
=3D --_a9f2e642-c7a4-4a8f-a5c9-7cbe888bf492_--