Nice measurements
I would guess that the measurement uncertainty (and modeling uncertainty) is
sufficiently large that the modeled and measured are the same.
Reactance of 22.5 uH at 1.8 MHz is 1480 ohms, so given a Q of 570, that works
out to around 2.6 ohms AC resistance. A change of 5% would be 20 milliohms,
which isn't very much.
On Mon, 18 Aug 2025 08:35:13 -0700, Brian Beezley <k6sti@att.net> wrote:
I borrowed a coil from QCoil Inductors to measure with my HP 4342A Q meter.
This coil did not have the black, UV-resistant dielectric spreaders of
production coils, but it was otherwise the same. Here's what I tested:
23 turns #10 wire
Coil length = 6.25"
Coil diameter = 3.625"
Length of each #10 lead = 4.25"
All dimensions are wire center to wire center. I supported the coil
horizontally above the 4342A by its leads. The side of the coil nearest
the 4342A enclosure was 3.25" above it.
Measurements followed by results from coil.exe:
MHz Q uH Calculated
1.8 580 22.6 547 22.4
3.7 730 23.7 753 23.5
The 3.7 MHz measurement was highly sensitive to my hands on the Q meter.
I positioned them for maximum Q. I figured that current through lossy
flesh can only reduce Q.
I modeled annealed copper wire. The wire was very stiff. Calculated Q
for hard-drawn copper was 536 and 739. At these frequencies the
dielectric composition of the four 0.25 rods I modeled embedding the
turns (Air Dux style) had virtually no effect.
https://qcoil.net
https://k6sti.neocities.org/coil.htm
Brian
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