[TowerTalk] Loading Coils

[Richard (Rick) Karlquist]

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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