Folded Resonator

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Folded Resonator
From: Tesla List <tesla-at-stic-dot-net>
Date: Tue, 24 Feb 1998 20:47:43 -0600
Approved: tesla-at-stic-dot-net

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From:  Vivian [SMTP:V.C.Watts-at-btinternet-dot-com]
Sent:  Monday, February 23, 1998 1:41 PM
To:  Tesla List
Subject:  Re: Folded Resonator

>
>----------
>From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
>Sent:  Sunday, February 22, 1998 4:52 PM
>To:  tesla-at-pupman-dot-com
>Subject:  Folded Resonator
>
>Hi all,
>        I wound a folded resonator in the weekend (expt #2). I first
>heard about this concept from my good friend in England, Richard
>Craven who was on the list at one time. Richard is an RF engineer.
>
>     Coil details: Bottom 2/3 wound in one direction, top 1/3 wound
>                   in the opposite direction.
>     Winding height: 13"
>     Diameter: 2.6"        h/d exactly 5
>     Turns: approx 1000
>     Copper diameter: 0.3mm
>
>I measured using the standard base-feed from a sig gen and hanging
>scope probe, first one way up (a) and then the other (b).
>
>(a) Cdist calculated from Medhurst to be 5.35pF
>    Lmeas on inductance meter = 8.42mH (if it had been wound all in
>          the same direction, Wheeler suggest a figure of 11.93mH odd)
>    Fr measured = 750kHz  (which agrees with measured L an calculated
>          C spot-on.
>
>I didn't measure Q because of interference from several powerful
>transmitters in my home vicinity which made graticule readings
>difficult to get to any degree of accuracy. However, it looked pretty
>high (sharp tuning).
>     With a topload consisting of a 4.3" diameter sphere mounted 0.7"
>above the top of the winding Fr dropped to 582.8kHz which left Csph
>calculated from this looking like 3.5pF (quite believable).
>Of particular note was an absence of spurii for the level I was able
>to test at.
>
>(b) Lmeas dropped to 8.4mH
>    Fr for the bare resonator: 803kHz odd
>    With the sphere, Fr = 724kHz
>
>Spurii was noted at 1.7Mhz without the sphere and 1.67MHz with.
>I will give this a spark test in mode (a) in both 2-coil and mag
>configuration after the join in the wire is properly insulated.
>
>Malcolm
>
>
>
Hi Malcolm
    So presumably this has similar characteristics as a coil only 1/3 the
length you created.  What advantage are you expecting from this particular
configuration?

Regards

Viv Watts UK.