Return-Path: Received: from mtain-dd02.r1000.mx.aol.com (mtain-dd02.r1000.mx.aol.com [172.29.64.142]) by air-ma10.mail.aol.com (v129.4) with ESMTP id MAILINMA102-b5414d870d15197; Mon, 21 Mar 2011 04:32:21 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dd02.r1000.mx.aol.com (Internet Inbound) with ESMTP id 3D83738000094; Mon, 21 Mar 2011 04:32:19 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Q1aVp-0002fO-N5 for rs_out_1@blacksheep.org; Mon, 21 Mar 2011 08:30:53 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Q1aVo-0002fF-EW for rsgb_lf_group@blacksheep.org; Mon, 21 Mar 2011 08:30:52 +0000 Received: from cavuit02.kulnet.kuleuven.be ([134.58.240.44]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Q1aVm-0007eA-1k for rsgb_lf_group@blacksheep.org; Mon, 21 Mar 2011 08:30:52 +0000 Received: from smtps02.kuleuven.be (smtpshost02.kulnet.kuleuven.be [134.58.240.75]) by cavuit02.kulnet.kuleuven.be (Postfix) with ESMTP id C3BBE51C034 for ; Mon, 21 Mar 2011 09:30:40 +0100 (CET) Received: from ICTS-S-HUB-N1.luna.kuleuven.be (icts-s-hub-n1.luna.kuleuven.be [10.112.9.11]) by smtps02.kuleuven.be (Postfix) with ESMTP id BE110F3863 for ; Mon, 21 Mar 2011 09:30:40 +0100 (CET) Received: from ICTS-S-EXC2-CA.luna.kuleuven.be ([10.112.11.13]) by ICTS-S-HUB-N1.luna.kuleuven.be ([10.112.9.11]) with mapi; Mon, 21 Mar 2011 09:30:41 +0100 X-Kuleuven: This mail passed the K.U.Leuven mailcluster From: Rik Strobbe To: "rsgb_lf_group@blacksheep.org" Date: Mon, 21 Mar 2011 09:30:40 +0100 Thread-Topic: LF: Loop TX antennas at VLF? Thread-Index: AcvnhWcShfK6+TX6RziTmXEPDyCrOAAFzlBf Message-ID: References: <4D83D475.9090609@telus.net> <000b01cbe622$6a23f8d0$8d01a8c0@JAYDELL>, ,<4D86BD6F.8020006@telus.net> In-Reply-To: <4D86BD6F.8020006@telus.net> Accept-Language: nl-NL, nl-BE Content-Language: nl-BE X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: nl-NL, nl-BE MIME-Version: 1.0 X-KULeuven-Information: Katholieke Universiteit Leuven X-KULeuven-Scanned: Found to be clean X-KULeuven-Envelope-From: rik.strobbe@fys.kuleuven.be X-Spam-Score: 0.3 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,MAILTO_TO_SPAM_ADDR=0.276 Subject: RE: LF: Loop TX antennas at VLF? Content-Type: multipart/alternative; boundary="_000_BF4A524700075746A6467658DFC7102C88B2129D51ICTSSEXC2CAlu_" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.6 required=5.0 tests=HTML_20_30, HTML_FONTCOLOR_UNSAFE,HTML_MESSAGE,MAILTO_TO_SPAM_ADDR, TO_ADDRESS_EQ_REAL 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: 3039ac1d408e4d870d137a36 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) --_000_BF4A524700075746A6467658DFC7102C88B2129D51ICTSSEXC2CAlu_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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 curr= ent is about 32A. I don't have an idea what addional (ground) losses tha loop will suffer fr= om at 9kHz. The loop indictance was calculated 40uH (by Jim), so the loop has a reacta= nce 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 frequenc= y what means that at 9kHz these lossses are over 200 times less than on 13= 7kHz. 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 =3D 4.2 Ohm/1000ft for the shield and 3.3 Ohm/1000ft for the conducto= r. So 40m (133ft) of RG58 would be 0.56 Ohm for the shield and 0.25 Ohm fo= r shield and conductor in parallel. See http://www.emaxit.asia/htx/documen= t/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 Oh= m for shield and conductor in parallel. See http://www.hytamerica.com/Down= load/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 ________________________________ Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or= g] namens Scott Tilley [sthed475@telus.net] Verzonden: maandag 21 maart 2011 3:52 Aan: rsgb_lf_group@blacksheep.org Onderwerp: Re: LF: Loop TX antennas at VLF? Hi Rik I think I missed a message or two. What current level is the consensus fo= r 100W input at 9KHz into a reasonable loop? I missed how this was modele= d and wonder if my original assumptions where off base. Thanks for any clarification you can offer. 73 Scott VE7TIL On 3/19/2011 9:27 AM, Rik Strobbe wrote: Roger, the antenna reactance about 2.5 Ohm, so the antenna voltage (and thus capa= citor voltage) will be less than 100V. I assume that polypropylene caps that work fine on 137 and 500 will also= be OK at 9kHz. Farnell sells 1uF/275Vac at 0.44 Euro (10 QTY) and 0.1uF/305Vac at 0.32 Eu= ro (10 QTY), so for less than 10 Euro you should be able to tune the anten= na in 0.1uF steps. As the antenna Q is rather low (2.5/0.1 =3D 25) a 0.1uF= step should be OK for a first try. 73, Rik ON7YD - OR7T ________________________________ Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Roger Lapthorn [rogerlapthorn@gmail.com] Verzonden: zaterdag 19 maart 2011 12:47 Aan: rsgb_lf_group@blacksheep.org Onderwerp: Re: LF: Loop TX antennas at VLF? Rik, et al Actually I am beginning to think that this small VLF TX loop is not such= a totally daft idea after all. The main issue seems to be with the capaci= tors but these seem to be less onerous than winding a very big (and lossy)= coil. Certainly there sounds to be merit in a larger TX loop for /P opera= tion. Thanks everyone for the constructive feedback on this thread. Most interes= ting. 73s Roger G3XBM On 19 March 2011 10:42, > wrote: Rik, Roger, Jim, Mal There are soil losses to consider with the loop as well. At 185 kHz (Part= 15 lowfer band), I ran a 50' X 50' transmitting loop made from mil spec= RG-11 (copper braid) and the soil losses were about equal to the wire los= ses. Not sure what the soil loss would be at 9 kHz but it would be interes= ting to know. Jay W1VD WD2XNS WE2XGR/2 ----- Original Message ----- From: Rik Strobbe To: rsgb_lf_group@blacksheep.org Sent: Saturday, March 19, 2011 6:07 AM Subject: RE: LF: Loop TX antennas at VLF? Roger, as Jim calculated running 100W in a 10 x 10 m loop will give about 0.5uW= ERP (is you use 4 x 1.5mm wire in parallel instead of a single 3mm wire= in order to avoid skinn effect losses). Using more parallel wires of a co= ax cable might pump up the ERP to 1 or 2uW. Looks pretty poor, but will a vertical antenna of a similar size do better= ? At 9kHz the radiation resistance of a 10m high + 10m topload vertical 75uO= hm. The antenna capacitance is 110pF, a reactance of 161kOhm. What means that= you will need a loading coil of 2.84H (yep Henry). Apart from the fact th= at it will cost a lot on copper wire the coil losses will be high. You wil= l need a Q of 160 to reduce the losses to 1kOhm. In addition for such a sm= all antenna you can excpect several 100 Ohm ground loss, so let's assume= a total loss of 1500 Ohm. 100W TX power will result in about 0.25 A anten= na current and an ERP of about 8uW. That's 6 to 10dB better than the loop, but instead of some cheap cap's you= will need a monster coil. I ran it one on the online coil calculators and= it came up to a 2.5m high and 1.8m diameter coil with amost 10km of 1.5mm= Cu wire (weight 150kg). And running 0.25A into the antenna will result in= 40kV ! So, despite the vertical could be 10dB better than the loop, the loop seem= s much more easy (and cheap) to build. It might be easier and cheaper to get the extra 10dB by usung mor wire in= the loop and pump up the power. 73, Rik ON7YD - OR7T ________________________________ Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Roger Lapthorn [rogerlapthorn@gmail.com] Verzonden: vrijdag 18 maart 2011 23:02 Aan: rsgb_lf_group@blacksheep.org Onderwerp: Re: LF: Loop TX antennas at VLF? Yep, I guess you're right Scott. And you know better than most. Ah well,= it was an interesting idea to toss around. 73s Roger G3XBM On 18 March 2011 21:53, Scott Tilley > wrote: 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 cha= llenge 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 the= n 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 wou= ld 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 operatio= ns 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 yo= u, 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 -- 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 --_000_BF4A524700075746A6467658DFC7102C88B2129D51ICTSSEXC2CAlu_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
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. Ig= noring other losses and tuning the loop the current is about 32A.
I don't have an idea wha= t addional (ground) losses tha loop will suffer from at 9kHz.
The loop in= dictance 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,&nbs= p;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 rem= ind 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.
&nbs= p;
In an ealie= r 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 =3D 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 Oh= m for shield and conductor in parallel. See http://www= .emaxit.asia/htx/document/P0002/7807A.pdf
Better woul= d be RG8 with 1.2 Ohmm/1000ft for the shield and 1.9Ohm/1000ft for the con= ductur. 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<= /a>
But even RG= 8 would be no better that 4 x 1.5mm Cu wire in parallel.
&nbs= p;
73, Rik&nbs= p; ON7YD
&nbs= p;
&nbs= p;
 
Van: owner-rsgb_= lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Scott= Tilley [sthed475@telus.net]
Verzonden: maandag 21 maart 2011 3:52
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: Loop TX antennas at VLF?

Hi Rik

I think I missed a message or two.  What current level is the consens= us for 100W input at 9KHz into a reasonable loop?  I missed how this= was modeled and wonder if my original assumptions where off base.

Thanks for any clarification you can offer.

73 Scott
VE7TIL



On 3/19/2011 9:27 AM, Rik Strobbe wrote:
Roger,
 
the antenna reactance about 2.5 Ohm,= so the antenna voltage (and thus capacitor voltage) will be less than 100= V.
I assume that polypropylene caps tha= t work fine on 137 and 500 will also be OK at 9kHz.
Farnell sells 1uF/275Vac at 0.44 Eur= o (10 QTY) and 0.1uF/305Vac at 0.32 Euro (10 QTY), so for less than 10 Eur= o you should be able to tune the antenna in 0.1uF steps. As the antenna Q is rather lo= w (2.5/0.1 =3D 25) a 0.1uF step should be OK for a first try.
 
73, Rik  ON7YD - OR7T
 
Rik, et al

Actually I am beginning to think that this small VLF TX loop is not such= a totally daft idea after all. The main issue seems to be with the capaci= tors but these seem to be less onerous than winding a very big (and lossy)= coil. Certainly there sounds to be merit in a larger TX loop for /P operation.

Thanks everyone for the constructive feedback on this thread. Most interes= ting.

73s
Roger G3XBM

On 19 March 2011 10:42, <<= a href=3D"mailto:jrusgrove@comcast.net">jrusgrove@comcast.net> wrote:
Rik, Roger, Jim, Mal
 
There are soil losses to consider wit= h the loop as well. At 185 kHz (Part 15 lowfer band), I ran a 50' X= 50' transmitting loop made from mil spec RG-11 (copper braid) and th= e soil losses were about equal to the wire losses. Not sure what the soil loss would be at 9 kHz but it would be interesting= to know. 
 
Jay W1VD  WD2XNS  WE2XGR/2&= nbsp;  
 
 
----- Original Message -----
Sent: Saturday, March 19, 2011 6:07= AM
Subject: RE: LF: Loop TX antennas= at VLF?

Roger,
 
as Jim calculated running 100W in a= 10 x 10 m loop will give about 0.5uW ERP (is you use 4 x 1.5mm wire in pa= rallel instead of a single 3mm wire in order to avoid skinn effect losses)= . Using more parallel wires of a coax cable might pump up the ERP to 1 or 2uW.
 
Looks pretty poor, but will a vertic= al antenna of a similar size do better ?
 
At 9kHz the radiation resistance of= a 10m high + 10m topload vertical 75uOhm.
The antenna capacitance is 110pF, a= reactance of 161kOhm. What means that you will need a loading coil of 2.8= 4H (yep Henry). Apart from the fact that it will cost a lot on copper wire= the coil losses will be high. You will need a Q of 160 to reduce the losses to 1kOhm. In addition for such a sma= ll antenna you can excpect several 100 Ohm ground loss, so let's assu= me a total loss of 1500 Ohm. 100W TX power will result in about 0.25= A antenna current and an ERP of about 8uW.
That's 6 to 10dB better than the loop, but instead of some cheap cap'= s you will need a monster coil. I ran it one on the online coil calculator= s and it came up to a 2.5m high and 1.8m diameter coil with amost 10k= m of 1.5mm Cu wire (weight 150kg). And running 0.25A into the antenna will result in 40kV !
 
So, despite the vertical could be 10= dB better than the loop, the loop seems much more easy (and cheap) to buil= d.
It might be easier and cheaper to ge= t the extra 10dB by usung mor wire in the loop and pump up the power.=
 
73, Rik  ON7YD - OR7T&nb= sp;
 
 
Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Roger= Lapthorn [rogerlapthorn@gmail.= com]
Verzonden: vrijdag 18 maart 2011 23:02
Aan: rsgb_lf_group@= blacksheep.org
Onderwerp: Re: LF: Loop TX antennas at VLF?

Yep, I guess you're right Scott. And you know better than most. = Ah well, it was an interesting idea to toss around.

73s
Roger G3XBM

On 18 March 2011 21:53, Scott Tilley <sthed475@telus.net&= gt; wrote:
Hi Roger

The practicality of pumping 35A into a loop is not an easy task!  Cou= ple 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 rea= lly 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 parallel= ed wires) and maybe 200W then the ERPs are starting to get more useful.&nb= sp;

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 eas= ier 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@gma= il.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 wou= ld 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 yo= u, 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.u= k
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.u= k
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.u= k
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.u= k
http://www= .youtube.com/user/g3xbm
https= ://sites.google.com/site/sub9khz/
G3XBM   GQRP 1678    ISWL G11088

--_000_BF4A524700075746A6467658DFC7102C88B2129D51ICTSSEXC2CAlu_--