Re: NEC-LIST: Hi-Q inductors

RMC,

I used a similar test setup as I didn't want to travel to another
building to use a VNA. I series resonated the coil with a 470 pF ceramic
cap. The specified Q of the cap is 1000. It is not an NPO dielectric.

I do suspect the cap though as I rebuilt the coil along the lines of a
Miniductor. Enameled wire spaced one wire diameter with thin strips of
Kapton tape to hold the shape. The Q now measures 20. I will bring in a
mica capacitor tomorrow and get to the bottom of this.

I measured the voltage across the series LRC when driven from a 50 ohm
source (generator with a 10 dB attenuator on the output to ensure a 50
ohm source). I also measured the -3 dB points to confirm the Q.

   Dave Cuthbert

-----Original Message-----
From: nec-list-bounces+drcuthbert=micron.com_at_robomod.net
[mailto:nec-list-bounces+drcuthbert=micron.com_at_robomod.net] On Behalf Of
RMC
Sent: Monday, February 14, 2005 2:37 PM
To: nec-list_at_robomod.net
Subject: Re: NEC-LIST: Hi-Q inductors

> I built a solenoid inductor wound on a PVC Pipe form. The measured
> results are close to the K6STI results except for the exceptionally
low
> measured Q.
> Measured Q @ 2 MHz = 15

How did you measure the Q, though? Maybe your measurement method
resulted
in an anomalously low Q being recorded.

I think you need to resonate the inductor using an external C designed
to
resonate well away from the self-resonant frequency (say, a tenth of
that
value i.e. 2MHz is close enough to be a good figure) .

Then sweep a low Z-output sinusoidal generator across the resonant
point.

Detect the electric field using a probe antenna a couple of coil
diameters
away from the coil, and then detune the signal generator and measure the
3dB
points.

Then Q is found by f/delta f

If this still gives you a Q of 15, then it is likely because of
proximity to
objects capable of having emfs induced in them i.e. concrete floors,
metal
table legs etc.

RMC, England

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