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The N2PK VNA Brian Flynn GM8BJF

The N2PK VNA Brian Flynn GM8BJF. What is a VNA?. Measures the transmission and reflection properties of a network. Technique has been around since the 1970s Instrumentation is expensive Normally beyond the scope of amateurs. The H-P 8410 (History!). The H-P 8510 (Current).

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The N2PK VNA Brian Flynn GM8BJF

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  1. The N2PK VNABrian Flynn GM8BJF

  2. What is a VNA? • Measures the transmission and reflection properties of a network. • Technique has been around since the 1970s • Instrumentation is expensive • Normally beyond the scope of amateurs

  3. The H-P 8410 (History!)

  4. The H-P 8510 (Current)

  5. The H-P 8573C (Current)

  6. Why reflection and transmission? • The reflection and transmission properties can completely describe a network. • A “network” can be any device • A load is a one port network • Filters or amplifiers are two-port networks • Directional couplers are 3 or 4 port devices

  7. A one –port network

  8. The Smith Chart

  9. A two-port network • S11 is complex input reflection coefficient • S22 is complex output reflection coefficient • S21 is forward transmission coefficient (gain) • S12 is reverse transmission coefficient (isolation)

  10. Black box representation of circuits • Approach is very versatile • A knowledge of 4 S-parameters completely characterises the network. • The VNA is the means of making these measurements.

  11. The N2PK approach to VNA design • Commercial instruments work with a superhet based architecture • N2PK uses a direct conversion approach • Depends on direct digital synthesis of test signals and accurate phase detection

  12. N2PK VNA Block diagram

  13. PCB layout

  14. Back view

  15. The Reflection bridge

  16. Calibration • The accuracy of measurements depend on comparison with known standards. • Open circuit • Short circuit • 50 ohm load • Through piece

  17. Software • A large part of the instrument’s functionality is dependent on the software (which is freely downloadable). • N2PK • W3WWV – EXETER • GM3SEK – VNA4WIN

  18. N2PK

  19. N2PK

  20. Exeter

  21. Exeter

  22. VNA4WIN

  23. VNA4WIN

  24. N2PK a la GM8BJF

  25. The Reflection Bridge

  26. The Calibration Standards

  27. Plot of My 7MHz Dipole

  28. A Live Demonstration.

  29. Further Plans . Convert to USB (Plug n’ Pray) Extend frequency range Fast ADC conversion (allows real-time measurement)

  30. Acknowledgements • Paul Kiciak, N2PK • Greg Ordy, W8WWV • Ian White, GM3SEK • Giancarlo Moda, I7SWX • Lou Macknik, W8LI and Suja Raviraj

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