FWIW, your number for Q (673) agrees exactly with the number I get using
Medhurst's 1947 formula.
On 8/3/2025 10:19 PM, Brian Beezley wrote:
A photo at the QCoils website shows a coil attached to an HP 4275A LCR
meter. At 2 MHz the coil reads 47.69 uH with a Q of 600.
I modeled the coil as follows:
Frequency: 2 MHz
Turns: 38 (counted from photo)
AWG 10
Coil inside diameter: 3.75" (website says diameter is approx 3.75")
Coil length: 10" (from website)
Annealed copper, no plating
Four 0.375" support rods (no Q degradation for any plastic)
Results:
L 47.0 uH
Q 673
I believe what the HP meter says. The small zeros shown in the Q readout
may mean that accuracy is limited in those digits. Perhaps an HP expert
can chime in.
The wire distributor says the tinned wire conforms to ASTM B-33 and MIL-
SPEC A-A-59551. I looked up both and could not find a plating thickness
specification in either. But the measured and calculated Q figures
suggest that plating loss is insignificant at 2 MHz.
Coil calculator:
https://k6sti.neocities.org/coil
Brian
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