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Re: What is proximity effect? (was:litz)
Hi Finn,
Before replying to this, I visited your website to have a look
at your rotary. Looks very nice!
> Original Poster: Finn Hammer <f-hammer-at-post5.tele.dk>
>
> I need help to understand the nature of the proximity effect.
>
> Proximity effect has been mentioned before, as a reason not to use
> thich wire in secondary coils. I have come to understand it as that
> the HF will not flow in the parts of the wire, that is close to each
> other. (As if it was repelled, like magnetic lines of equal polarity)
>
> If the wires are divided into 4 quadrants, this would mean that there
> would be little current flowing in quadrants 1 and 3, like indicated
> in ASCI below.
>
> Please view in a fixed-width font such as Courier.
>
> +++++++++++ +++++++++++
> .++++ ++++ .++++ ++++
> ++.. +.. ++.. +..
> ++ .. 2 .. ++ ++ .. 2 .. ++
> + . ... + + . ... +
> + .. .. + + .. .. +
> + .. .. + + .. .. + +
> 1 ... + + 1 ... + +
> .. . 3 + + .. . 3 + + ..
> .. + + .. .. +
> + ... .. + + ... .. +
> + .. . + + .. . +
> +.. 4 .. ++ +.. 4 .. ++
> ++ .. ++ ..
> ++++ ++++ ++++ ++++
> +++++++++++ +++++++++++
>
>
> If we now take the skin effect into consideration, there is not much
> conductor left!, and perhaps quadrant 4 doesn`t conduct either?
Thick wire is better than thin in a closewind for scoring high Q.
However, with the same winding pitch using thiner wire (i.e. a space
wind), Q improves over the thick wire, at least that's what I've found.
I can only write that down to the proximity effect.
> But if this is true for a litz wire too, and the litz is twisted, then
> the current will have to jump from wire to wire along the turns,
> making the litz wire an undesirable choise on a level with braided
> shield.
There is a fundamental difference between Litz and braid - litz has
each strand insulated from the other. Braid does not. The
comparisons in performance could not be more stark at TC
frequencies. However, litz is reputed to lose its advantage over solid
qire at frequencies much beyond the high end of the broadcast
band (i.e. above 1.6MHz or so). Don't know about that - haven't tried
it.
Regards,
Malcolm