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Re: Making a Q-meter /

 

On Sat, 17 Sep 2022 at 17:02, John KN5L <john@...> wrote:
Hi Mikek,

Revisiting with my V-Meter prototype as shown in:
DUT = T50-2 37T #24 with 330pF C0G
Different L C components. VNWA BW Q measurement = 211 for these parts.

Peaked to VOM full scale = 1V out of fixture, AWG = 204mV
Q = 50 / .204 = 245? (3.3387 MHz peak)

3dB down = 0.7079

Best I can resolve with VOM is 0.71, measuring two frequencies;
3.3317 and 3.3456 MHz with difference = 0.0139 MHz
Q = 3.3387 / 0.0139 = 240

Nice Match!

Which then questions, which is correct VNWA BW or prototype Voltmeter
with injection transformer?

John

Almost certainly neither is correct.??? The challenge will be to determine the uncertainty of each method, but even for simple instruments, working out the uncertainty is a non-trivial process.?

It would be interesting to put your VNA bandwidth measurements through the code in the big (100+ page) document from NPL about Q measurement with a VNA. That doesn¡¯t just use 3 points, but multiple points.?

The NPL document is in the files section of the group.?

Dave?
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...

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