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,
>
>> 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
>
>
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