Return-Path: Received: from mtain-ma04.r1000.mx.aol.com (mtain-ma04.r1000.mx.aol.com [172.29.96.12]) by air-db05.mail.aol.com (v129.4) with ESMTP id MAILINDB053-86474d83d4b0272; Fri, 18 Mar 2011 17:54:56 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-ma04.r1000.mx.aol.com (Internet Inbound) with ESMTP id F0883380000AA; Fri, 18 Mar 2011 17:54:53 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Q0hcS-0006lo-0s for rs_out_1@blacksheep.org; Fri, 18 Mar 2011 21:54:04 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Q0hcR-0006lf-Bi for rsgb_lf_group@blacksheep.org; Fri, 18 Mar 2011 21:54:03 +0000 Received: from defout.telus.net ([199.185.220.80]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Q0hcO-0007go-VF for rsgb_lf_group@blacksheep.org; Fri, 18 Mar 2011 21:54:03 +0000 Received: from edtncm03 ([199.185.220.221]) by priv-edtnes28.telusplanet.net (InterMail vM.8.01.03.00 201-2260-125-20100507) with ESMTP id <20110318215357.ZSJO6613.priv-edtnes28.telusplanet.net@edtncm03> for ; Fri, 18 Mar 2011 15:53:57 -0600 Received: from [192.168.1.74] ([75.157.174.214]) by edtncm03 with bizsmtp id Lltx1g00K4dur2b01ltx9f; Fri, 18 Mar 2011 15:53:57 -0600 X-Telus-Outbound-IP: 75.157.174.214 X-Authority-Analysis: v=1.1 cv=qJkQFdQ48ZbK16dQTlA9duG84kZgQD4m081ovRDdU+I= c=1 sm=2 a=jVez_htjv6wA:10 a=4aPOdFJL9SoA:10 a=pGLkceISAAAA:8 a=fnYqA7hvAAAA:8 a=j6Q1dnSHAAAA:8 a=A06HpNCPAAAA:20 a=8P0jffWtAAAA:20 a=EglTKO_tDJle4ANMyNkA:9 a=Y3fk4acUsJCpIvZJtuAA:7 a=0KX8gOCrF2Es2UvYTD8zUwbOE8gA:4 a=wPNLvfGTeEIA:10 a=MSl-tDqOz04A:10 a=gA6IeH5FQcgA:10 a=NWVoK91CQyQA:10 a=A92tgLIASMopcGcV:21 a=dJhyyFJqEm4Ecp0O:21 a=E49TIHS_x4-e5x83UUEA:9 a=mBYbA_R5-Jd19E6zGEQA:7 a=AcL5xz11LX7Gb4juBmqGbZDEP0QA:4 a=Sh4Bctt5u2vdDEYP:21 a=w-iDvHuQ-scWeHrR:21 Message-ID: <4D83D475.9090609@telus.net> Date: Fri, 18 Mar 2011 14:53:57 -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: In-Reply-To: X-Spam-Score: 1.4 (+) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,RATWARE_GECKO_BUILD=1.426 Subject: Re: LF: Loop TX antennas at VLF? Content-Type: multipart/alternative; boundary="------------080409050204080407080108" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.4 required=5.0 tests=FROM_ENDS_IN_NUMS,HTML_20_30, HTML_FONTCOLOR_UNSAFE,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: 3039ac1d600c4d83d4ad0612 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) --------------080409050204080407080108 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Hi Roger The practicality of pumping 35A into a loop is not an easy task! Couple this with the stability of most capacitors creates a real engineering challenge for a loop on 9KHz, notE the BW and Q. Not to mention really low ERP one would get. This will be an engineering challenge for sure! 73 Scott VE7TIL On 3/18/2011 2:39 PM, Roger Lapthorn wrote: > Hi All > > Just run Andy's spreadsheet for magnetic loops to see the sort of > figures we get at 8.9kHz. Assuming 100W and a loop diameter of 10m > with 3mm wire the efficiency works out at -87.4dB and the ERP -67.4dBW > (0.2uW). There is also the matter of the low loss 6211.7nF capacitor. > With larger loop diameters, thicker wire (or multiple paralleled > wires) and maybe 200W then the ERPs are starting to get more useful. > > The Marconi does seem a better bet, even with all the issues with > losses in the huge loading coil, but a VLF TX loop doesn't look a > total "no-hope" approach. Larger loops, with improved efficiencies, > may be easier than kite or balloon supported ones in a /P location. > > And then there is the widely spaced earthed electrode antenna..... but > I won't start a discussion on the merits or otherwise of this as I am > about to go on holiday this weekend and will not be able to respond to > emails next week. We know from work by DK7FC (and VLF professionals) > that this does work as a radiating structure. > > 73s > Roger G3XBM > > > > On 18 March 2011 14:09, Roger Lapthorn > wrote: > > Just wondering if anyone has done the maths to work out what sort > of ERP could be expected at 8.97kHz with, say, 100W to a smallish > loop antenna in the garden? > > It would certainly avoid the need for very very large matching > coils and may be easier to engineer than a Marconi. Even an > efficiency of -80dB would allow 1uW ERP and, judging by results > from G3XIZ with around 2uW, this could be useful with long stable > carrier transmissions of several hours. Most of us could run a > loop with an area of 100sq m. with thickish wire in our gardens. A > loop might also be more practical for portable operations perhaps > with a triangle with one high support. > > Certainly my own results with WSPR at 136 and 500kHz with just a > few watts and quite thin wire and around 80sq m loop area were > encouraging. Mind you, 9kHz is very much lower than 136kHz, so the > radiation resistance would be tiny I assume. > > 73s > Roger G3XBM > > -- > http://g3xbm-qrp.blogspot.com/ > http://www.g3xbm.co.uk > http://www.youtube.com/user/g3xbm > https://sites.google.com/site/sub9khz/ > G3XBM GQRP 1678 ISWL G11088 > > > > > -- > http://g3xbm-qrp.blogspot.com/ > http://www.g3xbm.co.uk > http://www.youtube.com/user/g3xbm > https://sites.google.com/site/sub9khz/ > G3XBM GQRP 1678 ISWL G11088 --------------080409050204080407080108 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Hi Roger

The practicality of pumping 35A into a loop is not an easy task!  Couple this with the stability of most capacitors creates a real engineering challenge for a loop on 9KHz, notE the BW and Q.  Not to mention really low ERP one would get. 

This will be an engineering challenge for sure!

73 Scott
VE7TIL

On 3/18/2011 2:39 PM, Roger Lapthorn wrote:
Hi All

Just run Andy's spreadsheet for magnetic loops to see the sort of figures we get at 8.9kHz. Assuming 100W and a loop diameter of 10m with 3mm wire the efficiency works out at -87.4dB and the ERP -67.4dBW (0.2uW). There is also the matter of the low loss 6211.7nF capacitor. With larger loop diameters, thicker wire (or multiple paralleled wires) and maybe 200W then the ERPs are starting to get more useful. 

The Marconi does seem a better bet, even with all the issues with losses in the huge loading coil, but a VLF TX loop doesn't look a total "no-hope" approach. Larger loops, with improved efficiencies, may be easier than kite or balloon supported ones in a /P location.

And then there is the widely spaced earthed electrode antenna..... but I won't start a discussion on the merits or otherwise of this as I am about to go on holiday this weekend and will not be able to respond to emails next week. We know from work by DK7FC (and VLF professionals) that this does work as a radiating structure.

73s
Roger G3XBM



On 18 March 2011 14:09, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:
Just wondering if anyone has done the maths to work out what sort of ERP could be expected at 8.97kHz with, say, 100W to a smallish loop antenna in the garden?

It would certainly avoid the need for very very large matching coils and may be easier to engineer than a Marconi. Even an efficiency of -80dB would allow 1uW ERP and, judging by results from G3XIZ with around 2uW, this could be useful with long stable carrier transmissions of several hours. Most of us could run a loop with an area of 100sq m. with thickish wire in our gardens. A loop might also be more practical for portable operations perhaps with a triangle with one high support.

Certainly my own results with WSPR at 136 and 500kHz with just a few watts and quite thin wire and around 80sq m loop area were encouraging. Mind you, 9kHz is very much lower than 136kHz, so the radiation resistance would be tiny I assume.

73s
Roger G3XBM

--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/
G3XBM   GQRP 1678    ISWL G11088



--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/
G3XBM   GQRP 1678    ISWL G11088

--------------080409050204080407080108--