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ms660 · 14th Sep 2017, 9:55 am

""I tried warming the coil up again, for longer this time. Again I saw an increase in Q which temporarily improved performance somewhat in the set, but again it didn’t last. Interestingly, the Q of the other two coils seemed to rise somewhat when the assembly was warm. This is the opposite effect to what I would’ve expected as wire resistance should surely increase with temperature. Can anyone think of a reason for this?""

Heating the wire causes expansion so maybe it's the skin effect, eg: more conductor CSA in the skin depth for RF?

Lawrence.

14th Sep 2017, 9:55 am	#24
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Marconi T21A Background Noise ""I tried warming the coil up again, for longer this time. Again I saw an increase in Q which temporarily improved performance somewhat in the set, but again it didn’t last. Interestingly, the Q of the other two coils seemed to rise somewhat when the assembly was warm. This is the opposite effect to what I would’ve expected as wire resistance should surely increase with temperature. Can anyone think of a reason for this?"" Heating the wire causes expansion so maybe it's the skin effect, eg: more conductor CSA in the skin depth for RF? Lawrence.