Return-Path: Received: from rly-mg07.mx.aol.com (rly-mg07.mail.aol.com [172.20.83.113]) by air-mg06.mail.aol.com (v123.4) with ESMTP id MAILINMG064-a234a099e0d3cd; Tue, 12 May 2009 12:05:30 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-mg07.mx.aol.com (v123.4) with ESMTP id MAILRELAYINMG075-a234a099e0d3cd; Tue, 12 May 2009 12:04:31 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1M3uSM-0003xe-9C for rs_out_1@blacksheep.org; Tue, 12 May 2009 17:03:50 +0100 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1M3uSL-0003xV-MP for rsgb_lf_group@blacksheep.org; Tue, 12 May 2009 17:03:49 +0100 Received: from yw-out-1718.google.com ([74.125.46.158]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1M3uSJ-0001dt-GQ for rsgb_lf_group@blacksheep.org; Tue, 12 May 2009 17:03:49 +0100 Received: by yw-out-1718.google.com with SMTP id 9so32379ywk.64 for ; Tue, 12 May 2009 09:02:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=0EHAmdoKnkkmUs2yAm3pmjWNUQVXsUYQyNebpxZel34=; b=pV3EVIcg9HWmPaKsyeGMN0o58hCkVKRmop2sTeOa85ZWrvzXQ5imEYbOH4tc4Q7r2V 2Tsktpk6D7kEvFr4rr8rE7ivSUkaN4xRM9O+qeF1NhsODHBg03ya4KDHDSHflfu0dc9B Y5x+XVylOPNcPydKyXeLK6X6pcdCmoCemadgw= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=omgxNT1O6q5Fkh9a6cDU1YjG0Hk0dsPpP8UdVO9Fdv3c0LEjf56M8Y78ch1YC2Iixi Bby8/yvm6crUu7Dd6odNDnQZTuwtDR+6YCDlkF36TGH8ae+CdvV+k2gxBN5mD0NzhYOV lu5rASxRv28a5/ONFQycfRvAP3BYnwEvC9odA= MIME-Version: 1.0 Received: by 10.151.68.3 with SMTP id v3mr15913ybk.165.1242144165620; Tue, 12 May 2009 09:02:45 -0700 (PDT) In-Reply-To: References: <4A01AEA0.1030308@btconnect.com> <003801c9cfed$3754c170$0301a8c0@mal769a60aa920> <4A094F88.31094.2E46CD4@mike.dennison.ntlworld.com> <007401c9d2fa$863a6280$0301a8c0@mal769a60aa920> Date: Tue, 12 May 2009 17:02:45 +0100 Message-ID: <88d2415e0905120902x24259365o364835d11f09dd01@mail.gmail.com> From: lawrence mayhead To: rsgb_lf_group@blacksheep.org X-Karma: unknown: DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Re: Re: 500kHz Portable Content-Type: multipart/alternative; boundary=001e680f173cc088d20469b93905 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=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-IP: 193.82.116.20 X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-d287.2 ; domain : googlemail.com DKIM : pass X-Mailer: Unknown (No Version) --001e680f173cc088d20469b93905 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit I fully agree with Mike and Andy, any slope downward will reduce the effective height of the antenna, and hence its radiation resistance. This may not be too much of a problem on 500kHz where enough RF can be generated but on 136 not so good and on 73 useless. I have proved this in practice as well as by simulation. So there you are Mal. Laurie G3AQC 2009/5/12 Andy Talbot > A full quarter wave inverted L with sloping end is starting to become a > loop with the ground path forming part of the loop conductor, rather than a > vertical. ANY antenna that approaches more than about a tenth of a > wavelength cannot be treated as small any more, and must be considered in > its entirety. Such is obvious even before resorting to modelling. Mike was > referring to electrically short antennas where the downward sloping part > simply opposes the current flow in the upward path. > > A small amount of slope on a large capacity hat might not be too noticeable > in practice, as a lot of extra capacitance at the top could do more good > than its slope undoes. > > Please stop and actually think, and perhaps before being so rude > and treating all why don't own millions of hectares of farmland as > second-class radio-ams, you stop and read the exam question. > > Andy G4JNT > wobbleU cubed .g4jnt.kom > > > 2009/5/12 mal hamilton > > You are certainly NO EXPERT at amateur radio never mind LF/MF and >> especially antennas. >> I have worked the world on LF/MF using Inv L antennas with the far end >> just above ground , and in normal CW mode. >> Some time ago it was Comics, elevated lemonade bottles as coil formers, >> thought an AR88D was a diversity fly catcher. >> What is coming next? The diversity UMBRELLA!!!! >> My current MF antenna is a full 1/4 wave inv L, 100 ft high and performs >> well but for some this might be difficult, therefore use what you can get on >> your property and let the far end tilt down if necessary. >> G3KEV >> >> ----- Original Message ----- From: "Mike Dennison" < >> mike.dennison@ntlworld.com> >> To: >> Sent: Tuesday, May 12, 2009 10:29 AM >> Subject: Re: LF: Re: Re: 500kHz Portable >> >> >> You do not need 2 masts for an inv L or T antenna. >>>> The so called horizontal wire(s) can slope down and the far end tied >>>> to a bush or tree, or a stake in the ground via an insulator, as far >>>> away as possible from the vert section, the longer the better. Keep it >>>> simple. mal/g3kev >>>> >>> >>> This is quite wrong. Any slope downwards will reduce the effective >>> height of a Marconi. Since ERP is a function of the square of the >>> effective height this is extremely important. An umbrella is far >>> preferable to an inverted-L in a single mast situation because a >>> large amount of capacitance to ground can be achieved without much >>> reduction of effective height. >>> >>> Based on my experience of LF portable (both on 73 and 136kHz), my >>> advice is to make very sure that the remote ends of a Marconi are >>> very well insulated as they carry large voltages. Keep well away from >>> wet trees. This is not just a safety issue; any voltage leaked is >>> power lost. >>> >>> Mike, G3XDV >>> ========== >>> >>> >>> >> >> >> -------------------------------------------------------------------------------- >> >> >> >> No virus found in this incoming message. >> Checked by AVG - www.avg.com >> Version: 8.5.325 / Virus Database: 270.12.25/2109 - Release Date: 05/11/09 >> 16:14:00 >> >> >> > --001e680f173cc088d20469b93905 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable I fully agree with Mike and Andy, any slope downward will reduce the effecti= ve height of the antenna, and hence its radiation resistance.
This may no= t be too much of a problem on 500kHz where enough RF can be generated but on= 136 not so good and on 73=A0 useless.
I have proved this in practice as well as by simulation.
So there you are= Mal.
Laurie G3AQC

2009/5/12 Andy Talb= ot <andy.g= 4jnt@googlemail.com>
A full quarter= wave inverted L with sloping end is starting to become a loop with the grou= nd path forming part of the loop conductor, rather than a vertical.=A0=A0 AN= Y antenna that approaches more than about a tenth of a wavelength cannot be=20= treated as small any more, and must be considered in its entirety.=A0 Such i= s obvious even before resorting to modelling.=A0 Mike was referring to elect= rically short antennas where the downward sloping part simply opposes the cu= rrent flow in the upward path.=A0=A0=A0
=A0
A small amount of slope on a large capacity hat might not be too notice= able in practice, as a lot of extra capacitance at the top could do more goo= d than its slope undoes.
=A0
Please stop and actually think, and perhaps before being so rude and= =A0treating all why don't own millions of hectares of farmland as second= -class radio-ams, you stop and read the exam question.

Andy =A0G4JNT
wobbleU cubed .g4jnt.kom


=
2009/5/12 mal hamilton <g3kevmal@talktalk.net= >

You are certainly N= O EXPERT at amateur radio never mind LF/MF and especially antennas.
I hav= e worked the world on LF/MF using Inv L antennas with the far end just above= ground , and in normal CW mode.
Some time ago it was Comics, elevated lemonade bottles as coil =A0formers, t= hought an AR88D was a =A0diversity fly catcher.
What is coming next? The=20= diversity UMBRELLA!!!!
My current MF antenna is a full 1/4 wave inv L, 10= 0 ft high and performs well but for some this might be difficult, therefore=20= use what you can get on your property and let the far end tilt down if neces= sary.
G3KEV

----- Original Message ----- From: "Mike Dennison" &l= t;mike.denni= son@ntlworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, May 12, 2009 10:29 AM
Subject: Re: LF: Re: Re: 500kHz Port= able


You do not need 2 m= asts for an inv L or T antenna.
The so called horizontal wire(s) can slop= e down and the far end tied
to a bush or tree, or a stake in the ground via an insulator, as far
away= as possible from the vert section, the longer the better. Keep it
simple= . mal/g3kev

This is quite wrong. Any slope downwards wil= l reduce the effective
height of a Marconi. Since ERP is a function of the square of the
effecti= ve height this is extremely important. An umbrella is far
preferable to a= n inverted-L in a single mast situation because a
large amount of capacit= ance to ground can be achieved without much
reduction of effective height.

Based on my experience of LF portable=20= (both on 73 and 136kHz), my
advice is to make very sure that the remote e= nds of a Marconi are
very well insulated as they carry large voltages. Ke= ep well away from
wet trees. This is not just a safety issue; any voltage leaked is
power l= ost.

Mike, G3XDV
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D




--------------------------------------------------------------= ------------------



No virus found in this incoming message.
Checked by AVG - www.avg.com
Version: 8= .5.325 / Virus Database: 270.12.25/2109 - Release Date: 05/11/09 16:14:00



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