SNA DCpl

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This page describes the Directional Coupler/Reflectometer for the rev0SNA 50-2500 MHz Scalar Network Analyzer.

Summary

Schematic for the rev0VTx VCO.
Board for the rev0VTx VCO.

The Directional Coupler/Reflectometer is based around the Mini-Circuits JDC-20-5 50-1500 MHz and SYD-20-33 30-3000 MHz 20dB Directional Couplers. The PCB includes a SKY65017 20dB amplifier, three SPDT RF switches, and necessary support components to allow switching between the low-frequency optimized JDC-20-5 coupler and high-frequency optimized SYD-20-33 coupler. The expected performance is >20dB directivity from 50-2500 MHz, allowing a +/-3dB error at 10dB return loss (2:1 VSWR) across the frequency range, with +/-3dB error at 24dB 15dB return loss (1.13:1 1.45:1 VSWR) at the 2m ham band, and +/-3dB error at 11.3dB 20dB return loss (1.75:1 1.22:1 VSWR) at the 70cm ham band.

Testing

  • 11.17.2013: The PCB was assembled with all components.
  • 11.18.2013: Through testing it was determined that the PCB was designed incorrectly to only display forward coupling, rather than reverse (needed to measure reflection power). The low frequency coupler was re-routed via semi-rigid coax to the correct orientation. Test results show >20dB directivity from 10-540 MHz, less than the datasheet specification of 50-1500 MHz (seen below).
Antenna measured via VNA directly vs. via directional coupler illustrating error vs. return loss and directivity.
Performance characteristics of the low frequency side of the directional coupler.

Revisions

  • 1.0: Initial revision.

Bill of Materials (v1.0)

Part Quantity Unit Cost Total Cost Source
JDC-20-5 1 $17.95 $17.95 Mini-Circuits
SYD-20-33+ 1 $21.95 $21.95 Mini-Circuits
SKY65017 1 $1.63 $1.63 Digi-Key
AS179-92LF 3 $0.52 $1.56 Digi-Key
74LVC1GU04 1 $0.38 $0.38 Digi-Key
0402 100nF Capacitor 11 $0.011 $0.12 Digi-Key
0402 10pF Capacitor 1 $0.0116 $0.01 Digi-Key
0603 Capacitor 6 $0.0096 $0.06 eBay - mib_instruments
0402 Resistor 10 $0.025 $0.25 eBay - mib_instruments
0603 Ferrite Bead (1500 Ohm) 1 $0.21 $0.21 Digi-Key
Male Header 3 $0.01 $0.03 eBay
SMA Female Connector 3 $3.37 $10.11 Digi-Key
PCB 1.725"x0.95"/3 $10.00 $5.46 Laen's PCB
Total Unit Cost $59.72

PCB/Construction Photos