A SIMPLE CRYSTAL NOTCH CIRCUIT FOR NOISE MEASUREMENTSJacques AudetVE2AZXjacaudet [at] videotron [dot] ca I used Mini Circuits

ZFSC-2-4 BroadbandCombiner/Splitter

OUT

PORT

IN

PORT

XTALTuner

FROM: 50 ΩGENERATORUnder Test

TO: 50 ΩSPECTRUMANALYZER

12 M

Hz

Cry

stal

5 Ω

ESR

Crystal Tuning CapacitorAdjust for best notch

Adjust tuner forbest notch

~100 ΩControlsNotchWidth

200 Ω

Combiner/splitter

R

Shielded

MFJ Antenna Tuner

L

References:Oscillator Noise Evaluation with a crystalNotch Filter by Wes Hayward, W7ZOIQEX July/August 2008

HP RF & Microwave Phase NoiseMeasurement Seminar

Select L to resonateabove and below XTALfrequency.

SIMULATIONS

20 Hz Span

R=0 Ω

R=100 Ω

SIMULATIONS

200 Hz Span

R=0 Ω

R=100 Ω

SIMULATIONS

2 KHz Span

R=0 Ω

R=100 Ω

SIMULATIONS

20 KHz Span

R=0 Ω

R=100 Ω

NOTCH MEASUREMENTS

20 Hz Span

NOTCH MEASUREMENTS

200 Hz Span

NOTCH MEASUREMENTS

2 KHz Span

NOTCH MEASUREMENTS

20 KHz Span

NOTCH MEASUREMENTS

200 KHz Span

+55 KHz-21.2 dB

+97 KHz-15.6 dB

+135 KHz-9.5 dBNot shown

MEASUREMENTS on Marconi 2019A Signal Generator (set at 0 dBm, 12.00000 MHz)

Calibration signalTuner disconnected

20 KHz SpanLevel = -6.86 dBm

10 dB/div50 traces averaged

MEASUREMENTS on Marconi 2019A Signal Generator (set at 0 dBm, 12.00000 MHz)

Carrier nulledwith tuner andXTAL series LC

20 KHz SpanLevel = -68.28 dBmDelta = 61.4 dB

10 dB/div50 traces averaged -94 dBc

-61.4 dBc

Shows residual generator noise, after carrier has been notched by -6.86 – (-68.28) = 61.4 DbCorrection at 2 KHz: add 3 dB. Effective BW = 300 Hz x 1.2 = 360 or - 25.6 dB / Hz Random signal Correction = +2.5 dBExample at 2 KHz offset, graph reads -103 dBc + 3 - 25.6 + 2.5 = -123 dBc/Hz. At 10 KHz offset: -134 dBc/Hz