Message-ID: <C33AF569AF2D4CB2B8A4B6E059543542@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <CAA8k23Rn9WpQM3Ukf=cq5-bLmWy+o4SEsH2abf7cAX=BpLWExQ@mail.gmail.com> <op.v6k16ktpyzqh0k@pc-roelof> <033201ccbcab$5c5fe640$1502a8c0@Clemens04> <op.v6mtuugnyzqh0k@pc-roelof> <000901ccbcc4$42768fe0$c763afa0$@com> <4EECC1E8.4000806@iup.uni-heidelberg.de> <002c01ccbd6f$572761c0$0401a8c0@xphd97xgq27nyf> <39D91133A64A480596FBAA4395D85812@JimPC> <007901ccbd9e$69fe2ed0$0401a8c0@xphd97xgq27nyf> <08C805D2A1C04E64836275C632577CF2@JimPC>
In-Reply-To: <08C805D2A1C04E64836275C632577CF2@JimPC>
Date: Mon, 19 Dec 2011 12:26:08 -0000
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Subject: Re: LF: Re: TX system at DK7FC, schematic
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''The helium was just a sales  gimmick''

And  beloved of those  who  talk like  Donald Duck !

G..

--------------------------------------------------
From: "James Moritz" <james.moritz@btopenworld.com>
Sent: Monday, December 19, 2011 9:36 AM
To: <rsgb_lf_group@blacksheep.org>
Subject: LF: Re: TX system at DK7FC, schematic

> Dear Mal, LF Group,
>
>> The highest Q coils I have seen are self supporting encased in a helium
>> container and the Q specified was only in a few hundred. What sort of 
>> coil
>> construction yields 4000 and above ?
>> I have yet to encounter such a specimen
>
> Errm.... The sort of specimen shown in the picture you sent to everyone 
> yesterday, i.e., a coil a few metres in diameter wound using very large 
> litz wire.
>
> The highest Q LF coil I have made so far had 109 turns of 729-strand litz 
> wire wound on a plastic former about 400mm diameter. L was about 4mH and Q 
> measured at 1100. Stefan's loading coil uses similar construction and has 
> similar Q. A coil of similar size and inductance wound with PVC insulated 
> copper wire had a Q of only about 300.
>
> For a given inductance and type of construction, Q increases with size, 
> but only slowly. The size required to reach a given Q seems to reduce 
> fairly slowly with increasing frequency. This is part of the reason for 
> VLF loading coils being so large. The "helium coils" were discussed on 
> this reflector some time ago - they were loading coils for HF mobile 
> whips. A Q of a few hundred for a fairly large coil  is not remarkable; 
> obviously, the size of coil is limited for a practical mobile whip. The 
> helium was just a sales gimmick that would make no significant difference 
> to Q.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>