''The helium was just a sales gimmick''
And beloved of those who talk like Donald Duck !
G..
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From: "James Moritz" <[email protected]>
Sent: Monday, December 19, 2011 9:36 AM
To: <[email protected]>
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
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