Message-ID: <000901ccbe3e$31cd2700$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
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>
Date: Mon, 19 Dec 2011 11:06:01 -0000
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Subject: LF: Re: Re: TX system at DK7FC, schematic
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Hi Jim es LF
My LF loading coil as described recently is wound with ex Decca litz 729
strand wire wound on a semi air spaced plastic basket
I avoid using a variometer which would degrade the main coil Q
mala/g3kev

----- Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, December 19, 2011 9:36 AM
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
>
>