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From: John Rabson <john.rabson@numeo.fr>
In-Reply-To: <08C805D2A1C04E64836275C632577CF2@JimPC>
Date: Mon, 19 Dec 2011 11:36:22 +0100
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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>
To: rsgb_lf_group@blacksheep.org
Subject: Re: ***CECI EST UN SPAM*** LF: Re: TX system at DK7FC, schematic
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When the 73 kHz band was made available in the UK, I asked Arnold Lynch =
(formerly of Post Office Research Department, Dollis Hill) about =
measuring high Q values. I believe the maximum he mentioned was 5000.

John F5VLF

On 19 Dec 2011, at 10:36CET, James Moritz wrote:

> Dear Mal, LF Group,
>=20
>> 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
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> Cheers, Jim Moritz
> 73 de M0BMU=20
>=20
>=20