Return-Path: Received: from mtain-df06.r1000.mx.aol.com (mtain-df06.r1000.mx.aol.com [172.29.64.218]) by air-da09.mail.aol.com (v129.4) with ESMTP id MAILINDA091-85eb4d848a28336; Sat, 19 Mar 2011 06:49:12 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-df06.r1000.mx.aol.com (Internet Inbound) with ESMTP id 50D76380000A4; Sat, 19 Mar 2011 06:49:10 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Q0thY-00031b-Py for rs_out_1@blacksheep.org; Sat, 19 Mar 2011 10:48:08 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Q0thX-00031S-GL for rsgb_lf_group@blacksheep.org; Sat, 19 Mar 2011 10:48:07 +0000 Received: from qmta06.emeryville.ca.mail.comcast.net ([76.96.30.56]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Q0thV-0002hD-Fi for rsgb_lf_group@blacksheep.org; Sat, 19 Mar 2011 10:48:07 +0000 Received: from omta16.emeryville.ca.mail.comcast.net ([76.96.30.72]) by qmta06.emeryville.ca.mail.comcast.net with comcast id LyiF1g0011ZMdJ4A6ynyvE; Sat, 19 Mar 2011 10:47:58 +0000 Received: from JAYDELL ([76.23.233.102]) by omta16.emeryville.ca.mail.comcast.net with comcast id Lyiw1g00c2DDHkk8cyixWB; Sat, 19 Mar 2011 10:42:58 +0000 Message-ID: <000b01cbe622$6a23f8d0$8d01a8c0@JAYDELL> From: To: References: <4D83D475.9090609@telus.net>, Date: Sat, 19 Mar 2011 06:42:58 -0400 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 X-Spam-Score: 0.8 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001,MAILTO_TO_SPAM_ADDR=0.276,NO_REAL_NAME=0.55 Subject: Re: LF: Loop TX antennas at VLF? Content-Type: multipart/alternative; boundary="----=_NextPart_000_0007_01CBE600.E26B9180" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.9 required=5.0 tests=HTML_20_30, HTML_FONTCOLOR_UNSAFE,HTML_MESSAGE,MAILTO_TO_SPAM_ADDR,NO_REAL_NAME 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: 3039ac1d40da4d848a2613f2 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none ------=_NextPart_000_0007_01CBE600.E26B9180 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit 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 losses. Not sure what the soil loss would be at 9 kHz but it would be interesting 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 coax 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 75uOhm. 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 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 small 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 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 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 seems 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 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 -- 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 ------=_NextPart_000_0007_01CBE600.E26B9180 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Rik, Roger, Jim, Mal
 
There are soil losses to consider wit= h the loop as=20 well. At 185 kHz (Part 15 lowfer band), I ran a 50' X 50' transmi= tting loop=20 made from mil spec RG-11 (copper braid) and the soil losses were= about=20 equal to the wire losses. Not sure what the soil loss would be at 9 kH= z but it=20 would be interesting to know. 
 
Jay W1VD  WD2XNS =20 WE2XGR/2   
 
 
----- Original Message -----
From:=20 Rik Strobbe
Sent: Saturday, March 19, 201= 1 6:07=20 AM
Subject: RE: LF: Loop TX ante= nnas at=20 VLF?

Roger,
 
as Jim calculated running 100W in= a 10 x 10 m=20 loop will give about 0.5uW ERP (is you use 4 x 1.5mm wire in paralle= l instead=20 of a single 3mm wire in order to avoid skinn effect losses). Using= more=20 parallel wires of a coax cable might pump up the ERP to 1 or 2uW.
 
Looks pretty poor, but will a vert= ical antenna=20 of a similar size do better ?
 
At 9kHz the radiation resistance= of a 10m high +=20 10m topload vertical 75uOhm.
The antenna capacitance is 110pF,= a reactance of=20 161kOhm. What means that you will need a loading coil of 2.84H (yep= Henry).=20 Apart from the fact that it will cost a lot on copper wire the coil= losses=20 will be high. You will need a Q of 160 to reduce the losses to 1kOhm= . In=20 addition for such a small antenna you can excpect several 100= Ohm ground=20 loss, so let's assume a total loss of 1500 Ohm. 100W TX power= will result=20 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 chea= p cap's=20 you will need a monster coil. I ran it one on the online coil=20 calculators and it came up to a 2.5m high and 1.8m diameter coi= l with=20 amost 10km of 1.5mm Cu wire (weight 150kg). And running 0.25A into= the antenna=20 will result in 40kV !
 
So, despite the vertical could be= 10dB better=20 than the loop, the loop seems much more easy (and cheap) to=20 build.
It might be easier and cheaper to= get the extra=20 10dB by usung mor wire in the loop and pump up the power.
 
73, Rik  ON7YD - OR7T&= nbsp;
 
&= nbsp;
Van:=20 owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.o= rg] namens=20 Roger Lapthorn [rogerlapthorn@gmail.com]
Verzonden: vrijda= g 18 maart=20 2011 23:02
Aan: rsgb_lf_group@blacksheep.org
Onderwe= rp:=20 Re: LF: Loop TX antennas at VLF?

Yep, I guess you're right Scott. And you know better than most.=   Ah=20 well, it was an interesting idea to toss around.

73s
Roger= =20 G3XBM

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

The practicality of pumpi= ng 35A into=20 a loop is not an easy task!  Couple this with the stability= of most=20 capacitors creates a real engineering challenge for a loop on 9KHz= , notE the=20 BW and Q.  Not to mention really low ERP one would get. = =20

This will be an engineering challenge for sure!

73= =20 Scott
VE7TIL=20


On 3/18/2011 2:39 PM, Roger Lapthorn wrote= :=20
Hi All

Just run Andy's spreadshee= t for=20 magnetic loops to see the sort of figures we get at 8.9kHz. Assu= ming 100W=20 and a loop diameter of 10m with 3mm wire the efficiency works ou= t at=20 -87.4dB and the ERP -67.4dBW (0.2uW). There is also the matter= of the low=20 loss 6211.7nF capacitor. With larger loop diameters, thicker wir= e (or=20 multiple paralleled wires) and maybe 200W then the ERPs are star= ting to=20 get more useful. 

The Marconi does seem a better be= t, even=20 with all the issues with losses in the huge loading coil, but a= VLF TX=20 loop doesn't look a total "no-hope" approach. Larger loops, with= improved=20 efficiencies, may be easier than kite or balloon supported ones= in a /P=20 location.

And then there is the widely spaced earthed el= ectrode=20 antenna..... but I won't start a discussion on the merits or oth= erwise of=20 this as I am about to go on holiday this weekend and will not be= able to=20 respond to emails next week. We know from work by DK7FC (and VLF= =20 professionals) that this does work as a radiating structure.=20

73s
Roger G3XBM



On 18 March 2011 14:09, Roger Lapthorn= <rogerlapthorn@gmail.com>=20 wrote:
Just=20 wondering if anyone has done the maths to work out what sort= of ERP=20 could be expected at 8.97kHz with, say, 100W to a smallish loo= p antenna=20 in the garden?

It would certainly avoid the need for= very very=20 large matching coils and may be easier to engineer than a Marc= oni. Even=20 an efficiency of -80dB would allow 1uW ERP and, judging by res= ults from=20 G3XIZ with around 2uW, this could be useful with long stable= carrier=20 transmissions of several hours. Most of us could run a loop wi= th an area=20 of 100sq m. with thickish wire in our gardens. A loop might al= so be more=20 practical for portable operations perhaps with a triangle with= one high=20 support.

Certainly my own results with WSPR at 136 and= 500kHz=20 with just a few watts and quite thin wire and around 80sq m lo= op area=20 were encouraging. Mind you, 9kHz is very much lower than 136kH= z, so the=20 radiation resistance would be tiny I assume.

73s
Ro= ger=20 G3XBM

--
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http://www.g3xbm.co.ukhttp://www.youtube.com/user/g3xbm
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G3XBM  =20 GQRP 1678    ISWL=20 G11088



--=
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http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
ht= tps://sites.google.com/site/sub9khz/
G3XBM  =20 GQRP 1678    ISWL=20 G11088



--
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http://www.g3xbm.co= .uk
http://www.youtube.com/user/g3xbm
https://sites= .google.com/site/sub9khz/
G3XBM   GQRP=20 1678    ISWL G11088
------=_NextPart_000_0007_01CBE600.E26B9180--