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LF: Re: TX system at DK7FC, schematic

To: <[email protected]>
Subject: LF: Re: TX system at DK7FC, schematic
From: "James Moritz" <[email protected]>
Date: Mon, 19 Dec 2011 09:36:58 -0000
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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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