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Folded Resonator
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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