Return-Path: X-Spam-DCC: paranoid 1233; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.4 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id tA7Fw7tw007049 for ; Sat, 7 Nov 2015 16:58:07 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Zv5pD-0007Ms-BV for rs_out_1@blacksheep.org; Sat, 07 Nov 2015 15:54:43 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Zv5pC-0007Mj-Ur for rsgb_lf_group@blacksheep.org; Sat, 07 Nov 2015 15:54:42 +0000 Received: from smtpout4.wanadoo.co.uk ([80.12.242.68] helo=smtpout.wanadoo.co.uk) by relay1.thorcom.net with esmtp (Exim 4.86) (envelope-from ) id 1Zv5o9-0003QO-Vv for rsgb_lf_group@blacksheep.org; Sat, 07 Nov 2015 15:54:41 +0000 Received: from AGB ([95.150.81.41]) by mwinf5d50 with ME id eftS1r00C0tVK6703ftSga; Sat, 07 Nov 2015 16:53:26 +0100 X-ME-Helo: AGB X-ME-Date: Sat, 07 Nov 2015 16:53:26 +0100 X-ME-IP: 95.150.81.41 Message-ID: <957601B31AB3407BB82F82515E15A9F1@AGB> From: "Graham" To: References: <1843908200.20151104162925@chriswilson.tv>, , <8E31BC8EB75546E59F99E35AFAAA0DEE@AGB> <563DD93A.22662.37C4EA@mike.dennison.ntlworld.com> <514333482.20151107111905@chriswilson.tv> <79AAC450664E4A62AE4F7F72331E43BC@gnat> <9E37EAD7DC7A43E08EFF3EAF82788F58@gnat> In-Reply-To: <9E37EAD7DC7A43E08EFF3EAF82788F58@gnat> Date: Sat, 7 Nov 2015 15:53:26 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 X-Scan-Signature: e2fb1a5df1e2bc3146a6f486b4640b03 Subject: Re: Re[2]: LF: Capacitive top hat question Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response Content-Transfer-Encoding: 7bit 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-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 4879 Im thinking of transformation, caused by a top loading coil . That would appear to offer a higher ground capacity from the top wires , after the coil , lowering the feed z at one side and higher at the other ? G, -------------------------------------------------- From: "Alan Melia" Sent: Saturday, November 07, 2015 3:24 PM To: Subject: Re: Re[2]: LF: Capacitive top hat question > Measured ....the only type that matters :-)) > Alan > ----- Original Message ----- > From: "Graham" > To: > Sent: Saturday, November 07, 2015 2:31 PM > Subject: Re: Re[2]: LF: Capacitive top hat question > > >> doubling the capacity ofan aerial halves the ground loss >> >> Actual or effective capacity ? >> >> G, >> >> -------------------------------------------------- >> From: "Alan Melia" >> Sent: Saturday, November 07, 2015 12:32 PM >> To: >> Subject: Re: Re[2]: LF: Capacitive top hat question >> >>> I think that maybe too much emphasis is placed on specific structures. >>> At these frequencies any structure of conductors can be resolved into an >>> equivalent vertical and horizontal arrangement......even a continuously >>> sloping wire!. As Mike says the horizonal portion does not radiate >>> appreciably because of the reflection in the close-by ground. >>> >>> Predominantly horizontal conductors will inrease the capacitance of the >>> aerial to ground and an extra run of wire will have most effect if >>> separated by around a metre to reduce interaction between to two. >>> Ball-park figure an extra 6pF per metre. The actual configuration of >>> connection is unimportant for the horizonals form a "skeleton" plate. >>> Note whereas Rugby LF station had originally caged wires between the 850 >>> foot masts to increase the capacity, after the rebuild the internal area >>> with the masts was "laced" with straight single wires. This produced >>> more capacity and was easier to maintain the the high windage cages. >>> >>> Then the more horizontal wire the higher the aerial capacity, so the >>> smaller the inductance needed to resonate it ......and lower coil loss. >>> However another effect not well modelledin aerial synthesis programs >>> isthat doubling the capacity ofan aerial halves the ground loss. There >>> are mesurements on my web site confirming this, under spiral aerials. >>> Halving ground loss is very difficult to achieve with extra groundrods >>> or "radials" at LF/MF unless it is poor to start with. The only >>> casewhere this is not useful is over very good ground, a high >>> water-table or possibly sea water. >>> >>> As to feeding Chris's loop as a loop..... the size is much less than a >>> wavelength and is too low compared with the wavelenth to radiate >>> efficiently. Any uncancelled radiation will probably be vertically >>> upwards, much of which will escape the ionosphere never to return. >>> Its performance at HF where distance above ground is of the same order >>> as a wavelength will be totally different. Phase difference round the >>> loop will lead to a totally different pattern of radiation. >>> >>> Alan >>> G3NYK >>> >>> >>> ----- Original Message ----- >>> From: "Chris Wilson" >>> To: "Mike Dennison" >>> Sent: Saturday, November 07, 2015 11:19 AM >>> Subject: Re[2]: LF: Capacitive top hat question >>> >>> >>>> Hello Mike, >>>> >>>> Saturday, November 7, 2015 >>>> >>>> >>>> Thanks for the info Mike, as always! Is there any real benefit in >>>> having the vertical section centralised within the top hat capacitive >>>> array, be it a horizontal loop, random horizontal wires, or a plain >>>> single wire? >>>> >>>> And is there much point in struggling to get one corner or side of a >>>> horizontal top hat loop higher than the rest, or the same for a single >>>> wire? I have some tall trees, but unfortunately not two tall trees >>>> opposite one another across free space, so whatever capacitive hat I >>>> fix up is likely to be significantly higher at one end or one corner. >>>> There's no point in struggling and risking life and limb to get one >>>> end as high as possible if it ends up only as efficient as the lowest >>>> end or point. >>>> >>>> >>>>> To all intents and purposes a short (in wavelengths) vertical >>>>> attached to an arrangement of horizontal wires is a simple >>>>> (capacitively) loaded vertical. >>>> >>>>> The horizontal part will radiate, especially if it has a vertical >>>>> component rising higher than the feedpoint, but most of that >>>>> radiation will be cancelled by its reflection in the ground. >>>> >>>>> Several unbelievers have tried using purely horizontal transmitting >>>>> antennas and have had poor results. The beauty of amateur radio is >>>>> that you can prove something to yourself, but it won't change the >>>>> laws of physics. >>>> >>>>> Of course, every electrically small Marconi that is not in free space >>>>> performs in a complex way, but the result of that complexity is small >>>>> compared to the predominent omnidirectional radiation from the >>>>> vertical section. There is very little difference between various >>>>> arrangements of capacity hat, so long as you follow the rule to put >>>>> up as much wire as possible, as high as possible and covering as much >>>>> ground as possible. >>>> >>>>> Mike, G3XDV >>>>> ========== >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> >>>> -- >>>> Best regards, >>>> Chris mailto:chris@chriswilson.tv >>>> >>>> >>> >>> >> > >