Return-Path: Received: from mtain-de01.r1000.mx.aol.com (mtain-de01.r1000.mx.aol.com [172.29.64.201]) by air-de02.mail.aol.com (v129.4) with ESMTP id MAILINDE023-5ea84d873727305; Mon, 21 Mar 2011 07:31:51 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-de01.r1000.mx.aol.com (Internet Inbound) with ESMTP id 77D41380000F8; Mon, 21 Mar 2011 07:31:48 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Q1dJb-0003Y9-UT for rs_out_1@blacksheep.org; Mon, 21 Mar 2011 11:30:27 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Q1dJa-0003Y0-Lx for rsgb_lf_group@blacksheep.org; Mon, 21 Mar 2011 11:30:26 +0000 Received: from defout.telus.net ([204.209.205.30]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Q1dJY-0000MY-HK for rsgb_lf_group@blacksheep.org; Mon, 21 Mar 2011 11:30:26 +0000 Received: from edmwcm03 ([204.209.205.13]) by priv-edmwes50.telusplanet.net (InterMail vM.8.01.03.00 201-2260-125-20100507) with ESMTP id <20110321113021.MYRA8015.priv-edmwes50.telusplanet.net@edmwcm03> for ; Mon, 21 Mar 2011 05:30:21 -0600 Received: from [192.168.1.74] ([75.157.141.251]) by edmwcm03 with bizsmtp id MnWK1g00t5Reinf01nWLkX; Mon, 21 Mar 2011 05:30:21 -0600 X-Telus-Outbound-IP: 75.157.141.251 X-Authority-Analysis: v=1.1 cv=b4z/0OdOO1iOt2/g1rdculf5PCmfBigCPKII37OguhM= c=1 sm=2 a=jVez_htjv6wA:10 a=7tQO1arQIyUA:10 a=kqtlx5UvAAAA:8 a=jy8Fa6mbAAAA:8 a=n3LGY4yd_uwvU3TeDIwA:9 a=BeJr59k6swml25Sn0lYA:7 a=tYhkvwe5ptznhQ8fRoCWoxqZLGMA:4 a=wPNLvfGTeEIA:10 a=ly2PjtKnln3cR7_RadcA:9 a=RvyMkVw10OJJhZ-4Pq0A:7 a=kVfmzdPLuKEsfMA4XtFyCD_RcbUA:4 Message-ID: <4D8736CB.8040509@telus.net> Date: Mon, 21 Mar 2011 04:30:19 -0700 From: Scott Tilley User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.15) Gecko/20110303 Lightning/1.0b2 Thunderbird/3.1.9 MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: <4D83D475.9090609@telus.net> <000b01cbe622$6a23f8d0$8d01a8c0@JAYDELL>, ,<4D86BD6F.8020006@telus.net> In-Reply-To: X-Spam-Score: 1.4 (+) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,RATWARE_GECKO_BUILD=1.426 Subject: LF: Loop TX antennas at VLF... Content-Type: multipart/alternative; boundary="------------090506030205050209040900" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.9 required=5.0 tests=FROM_ENDS_IN_NUMS,HTML_MESSAGE 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: 3039ac1d40c94d873724543c X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) --------------090506030205050209040900 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Hi Rik Thanks for this! I may be comparing apples to oranges alittle (maybe alot). The loop I have would only require a 1.8uF cap and this coupled with a higher Q makes for a little dicier tuning scenario. I concede this scenario is not as bad as I first thought when I thought about this briefly when Stephan enquired about a possible test from here many months ago. A careful review of your summary Rik was very helpful, thanks to all that contributed. The two big , and one minor design issues to get maximum potential from a loop down at 9KHz will be: 1) Current handling capability of the caps. 2) Tuning capability. 3) Ferrite saturation for the matching xfmr... Or should we use ferrite? #1 can be resolved, I think, as you have suggested with the use of LOTS of polypropylene caps... However, #2 will likely be the difficult one and be abit of an engineering challenge as the small loop proposed below may just get away with course tuning but as you get larger and reduce the Rac the Q goes up and so does the tuning criteria. This is where I got stuck with my original glimpses of thought on this. We can't rely on a good old vacuum variable so some sort of other idea... Hmmm, how about a special decade type box made of Polypropylene caps? The box could be designed once the loop's characteristics after installation have been bracketed in... The other downside of polypropylene caps will be there tendency to drift once you put alot of current into them, so you'll need lots! This drifting issue could be very problematic as I discovered on 137 with anything other than good transmitting micas with high current ratings at the operating frequency. Based on the results of others using mains transformers on 9KHz maybe item #3 is not a big problem after all? Anyone have a comment here? Looking forward to more ideas as this is tweaking my interest into building another tuner. 73 es TU Scott VE7TIL On 3/21/2011 1:30 AM, Rik Strobbe wrote: > Hello Scott, > the discussion is about a 10 by 10 meter loop and 100W RF power. > Using 4 x 1.5mm Cu wire (parallel) the DC resistance of a 10 by 10 > meter loop is about 0.1 Ohm. Ignoring other losses and tuning the loop > the current is about 32A. > I don't have an idea what addional (ground) losses tha loop will > suffer from at 9kHz. > The loop indictance was calculated 40uH (by Jim), so the loop has a > reactance of 2.3 Ohm at 9kHz. This means that the loop voltage is only > about 70V, so stray currents to the ground (or other grounded objects > near the loop) will be minimal and these losses can be ignored. > Other losses are due to induced currents (so called Eddy currents), > but if I remind well these losses are proportional to the square of > the frequency what means that at 9kHz these lossses are over 200 times > less than on 137kHz. > In an ealier mail I suggested to use coax cable as loop wire. > But to my own surprise Belden (main coax cable manufacturer) gives > rather large DC resistanses: > RG58 = 4.2 Ohm/1000ft for the shield and 3.3 Ohm/1000ft for the > conductor. So 40m (133ft) of RG58 would be 0.56 Ohm for the shield and > 0.25 Ohm for shield and conductor in parallel. See > http://www.emaxit.asia/htx/document/P0002/7807A.pdf > Better would be RG8 with 1.2 Ohmm/1000ft for the shield and > 1.9Ohm/1000ft for the conductur. 40m of RG8 would be 0.16 Ohm for the > shield and 0.1 Ohm for shield and conductor in parallel. See > http://www.hytamerica.com/Download/Private/file/PDF/belden/8237.pdf > But even RG8 would be no better that 4 x 1.5mm Cu wire in parallel. > 73, Rik ON7YD > --------------090506030205050209040900 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Hi Rik

Thanks for this!

I may be comparing apples to oranges alittle (maybe alot).  The loop I have would only require a 1.8uF cap and this coupled with a higher Q makes for a little dicier tuning scenario.  I concede this scenario is not as bad as I first thought when I thought about this briefly when Stephan enquired about a possible test from here many months ago. A careful review of your summary Rik was very helpful, thanks to all that contributed. 

The two big , and one minor design issues to get maximum potential from a loop down at 9KHz will be:
1) Current handling capability of the caps.
2) Tuning capability.
3) Ferrite saturation for the matching xfmr...  Or should we use ferrite?

#1 can be resolved, I think, as you have suggested with the use of LOTS of polypropylene caps...

However, #2 will likely be the difficult one and be abit of an engineering challenge as the small loop proposed below may just get away with course tuning but as you get larger and reduce the Rac the Q goes up and so does the tuning criteria.  This is where I got stuck with my original glimpses of thought on this.  We can't rely on a good old vacuum variable so some sort of other idea...

Hmmm, how about a special decade type box made of Polypropylene caps?  The box could be designed once the loop's characteristics after installation have been bracketed in...

The other downside of polypropylene caps will be there tendency to drift once you put alot of current into them, so you'll need lots!  This drifting issue could be very problematic as I discovered on 137 with anything other than good transmitting micas with high current ratings at the operating frequency. 

Based on the results of others using mains transformers on 9KHz maybe item #3 is not a big problem after all?  Anyone have a comment here?

Looking forward to more ideas as this is tweaking my interest into building another tuner.

73 es TU
Scott
VE7TIL

On 3/21/2011 1:30 AM, Rik Strobbe wrote:
Hello Scott,
 
the discussion is about a 10 by 10 meter loop and 100W RF power.
Using 4 x 1.5mm Cu wire (parallel) the DC resistance of a 10 by 10 meter loop is about 0.1 Ohm. Ignoring other losses and tuning the loop the current is about 32A.
I don't have an idea what addional (ground) losses tha loop will suffer from at 9kHz.
The loop indictance was calculated 40uH (by Jim), so the loop has a reactance of 2.3 Ohm at 9kHz. This means that the loop voltage is only about 70V, so stray currents to the ground (or other grounded objects near the loop) will be minimal and these losses can be ignored.
Other losses are due to induced currents (so called Eddy currents), but if I remind well these losses are proportional to the square of the frequency what means that at 9kHz these lossses are over 200 times less than on 137kHz.
 
In an ealier mail I suggested to use coax cable as loop wire.
But to my own surprise Belden (main coax cable manufacturer) gives rather large DC resistanses:
RG58 = 4.2 Ohm/1000ft for the shield and 3.3 Ohm/1000ft for the conductor. So 40m (133ft) of RG58 would be 0.56 Ohm for the shield and 0.25 Ohm for shield and conductor in parallel. See http://www.emaxit.asia/htx/document/P0002/7807A.pdf
Better would be RG8 with 1.2 Ohmm/1000ft for the shield and 1.9Ohm/1000ft for the conductur. 40m of RG8 would be 0.16 Ohm for the shield and 0.1 Ohm for shield and conductor in parallel. See http://www.hytamerica.com/Download/Private/file/PDF/belden/8237.pdf
But even RG8 would be no better that 4 x 1.5mm Cu wire in parallel.
 
73, Rik  ON7YD
 
 


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