Experiments with the DG8SAQ VNWA

Transcription

1 DG8SAQ VNWA Tutorial Experiments with the DG8SAQ VNWA and the SDR-Kits Test Board Tom BAIER DG8SAQ This is an excerpt from my Ham Radio 2013 presentation which has been slightly extended (slides 6, 20 and 21 added). 1

2 Test Board for HF Experiments Calibration Standards: Open = n.c. Short: Load =47Ω: Thru: 2

3 Measuring Load -Resistor without SOL- Calibration? Works, because VNWA TX and RX port impedances are exactly 50 Ω. Z x = 47 Ω yield 3,4 db insertion loss. only Thru calibration required! 3

4 Measuring Load -Resistor in Transmission (=S 21 -Measurement) Only Thru calibration required Measurement: Resistor between TX and RX 4

5 Measuring Load -Resistor Result = 46,6 Ω inductive part Analysis with Custom Trace n ta missio on dat nvert transm a to re eflectio Con data 5

6 S Reflection Data vs. Transmission Data 11 normalized impedance:! Z x z 50 S s 2( t S ) z S z 1 21 S t2( s S ) z 2 These conversions can be performed with VNWA Custom traces. 6

7 Simple Calibration Standard Model: Only measured Load-Resistance 7

8 SOL-Calibration SOL Calibration for S11-Measurement Measurement TX Short Open p Load 8

9 Reflexion Measurement (S 11 ) of a 1 nf Capacitor S 11 C capacitive ESR = loss Resonance due to component wires Capacitor reflects almost total power, S 11 0 db 9

10 Modelling of Measurement Result in VNWA using Custom-Trace Impedance to Reflecion coefficient i 0,984 nf 9,3 nh 0,22 Ω einfaches Modell 10

11 The Model is quite accurate! ktive! Induk 11

12 Two Port Measurement of a 12 khz Band Pass Filter S-Parameters applicable to low frequencies as well. The VNWA too! 12

13 Special VNWA Settings for low Frequencies Lowest sample rate 300 Hz Nyquist limit 150 Hz Measurements down to 150 Hz possible IF must be within Codec frequency range (20 Hz 16kHz) 13

14 SOLT-Calibration SOLT Calibration for 2 2-Port Port Measurements TX TX Short Open Load RX Thru 14

15 Beware: Steep Skirt Filters require Time to settle to changing Stimulus! 5 s sweep time 0,3 s sweep time 15

16 Two Port Measurement of a 12 khz Band Pass Filter We need to measure all four S-parameters (S 11, S 21, S 12, S 22 ) 16

17 Two Port Measurement of a 12 khz Band Pass Filter: Forward Measurement TX 1 2 RX S11, S21 measured 17

18 Two Port Measurement of a 12 khz Band Pass Filter: Reverse Measurement TX 2 1 S 12, S 22 measured RX 18

19 What are measured 2-Port S-Parameters good for? Optimum Match? 19

20 VNWA Matching Tool (1) Allows to recalculate 2-port S-parameters to source and load impedances different from 50 Ohms! 20

21 VNWA Matching Tool (2) Complex conjugate of source impedance = filter input impedance Complex conjugate of load impedance = filter output impedance 21

22 Matching Analysis with VNWA Matching Tool Optimum: Z in = Z out = 610 Ω 22

23 Forced Impedance Match using Resistors 50 Ω Ω = 610 Ω 23

24 Match works except for increased Loss Simulated with Matching Tool 21.8 db Measured with resistive match 24

25 Effect of two 560 Ω Resistors in Signal Path: VNWA Complex Calculator 21,7 db additional attenuation 25

26 This can also be properly simulated! Simulation Tool QUCS t/ Universal circuit simulator Free No restrictions Easy to use Grafics and data export needs brush up 26

27 Measured S-Parameters in QUCS measured S-parameters from s2p-file 27

28 Matching Simulation in QUCS Standard diagramm output a bit strange Export simulation result to VNWA 28

29 Comparison QUCS-Simulation vs. Measurement simulated measuerd with with QUCS VNWA PERFECT! 29

30 Free Filter Design Software (1): Elsie for LC-Filters LC-Filter Designer and Analyzer Student version restricted to 7 dipols Numerical simulation results export easily to s2p-file! 30

31 Free Filter Design Software (2): Dishal for Crystal Filters horst-dj6ev Crystal filter designer and analyzer Simulates without crystal losses S 21 -simulation results can be exported 31

32 Free Filter Design Software (3): AADE Filter Design - for all filters Univeral filter designer and analyzer Free, but with nag screen Easy to use Numerical simulation results cannot be exported 32

33 Design 3 Pole Butterworth π-band Pass for 5 MHz with 3 MHz Bandwidth at 50 Ω Filter Design with Elsie 33

34 Elsie Simulation Result 34

35 Modify Components to standard Values and finite Q simulation with finite Q 35

36 and export Simulation into s2p-file for Comparison with Measurement. Export 36

37 Filter Hardware 37

38 Comparison Measurement vs. Elsie Simulation S 21, S 11 measured - Plot1, Plot2 Elsie simulation e of uctor lel nance sindu paral reson serie 38

39 Measuring / Selecting Crystals: VNWA Crystal Analyzer eg e.g. transmission (S21-measurement) Thru standard d 39

40 The VNWA Crystal Analyzer Tool: Find 3 similar Crystals 40

41 With these we want to build a Crystal Filter Enter Crystal Parameters into AADE Daten vom VNWA Crystal Analyz er übertra agen 41

42 AADE Minimum Loss (Cohn) Design 186 Ω 66 pf 66 pf 66 pf 66 pf 186 Ω 42

43 Simulation in QUCS at 50 Ω using standard Component Values Crystals simulated with s1p-file obtained by VNWA measurement! 43

44 Crystal Filter Hardware 44

45 Crystal Filter: Measurement vs. Simulation at 50 Ω S 21, S 11 measurement - Plot1, Plot2 QUCS simulation 45

46 Crystal Filter: Measurement vs. Simulation at 186 Ω S 21, S 11 measurement - Plot1, Plot2 QUCS simulation 46

47 Now, we are able to Measure components Design filters Simulate filters Measure filters Try it for yourself! 47