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SWR Meter Session 3 Learn about Transformers and SWR Meters Forward Waves on Transmission Lines Z L = Zo (Characteristic Impedance) ZLZL V + - I Z load.

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Presentation on theme: "SWR Meter Session 3 Learn about Transformers and SWR Meters Forward Waves on Transmission Lines Z L = Zo (Characteristic Impedance) ZLZL V + - I Z load."— Presentation transcript:

1 SWR Meter Session 3 Learn about Transformers and SWR Meters Forward Waves on Transmission Lines Z L = Zo (Characteristic Impedance) ZLZL V + - I Z load = Zo (No reflected wave) Zo = 50 Ohms There is only a forward wave. V=+IZo SWR = 1.0 (No standing Wave) Transmitter F Load Port 1 Port 2

2 SWR Meter Reverse Waves on Transmission Lines Z L = Zo (Characteristic Impedance) ZLZL V + - I Here, Z L = Zo There is only a reverse wave V=-IZo SWR = 1.0 Transmitter R Port 1 Port 2 Current now reversed

3 SWR Meter Normally Z L not Equal to Zo Forward and Reverse Waves on the Line ZLZL V + - I Z L not equal to Zo Standing Waves exist Transmitter F Load R Port 1 Port 2 Forward wave reflects at load

4 SWR Meter Things to note in tests Forward wave power always greater than reverse wave power Forward wave power fixed for constant Tx Power Reverse wave power = 0 for Z L = Zo SWR 2:1 for Z L = 100 or 25 Ohms Meter actual measures Voltage and Current on the line SWR must be found from V FWD and V REV on the board

5 Kits and Parts meter T1 samples current T2 samples voltage RF appears at Diodes Diodes act as detectors Vrev and Vfwd measured SWR Calculated or Meters Calibrated

6 Marking the Transformers Two Transformers Mark the red dots as shown This is arbitrary I set the dots on the single turn

7 Set the other dots by inspection This is not arbitrary Marking the Transformers

8 Ideal Transformers N1=N2 Identical Windings Lenz and Faraday 1 mA B2 B1 B1+B2 =0 Lossless Lenz ZL

9 SWR Meter Circuit…modified Current in T1 Opposite direction for Forward and Reverse R4, R3 balance the bridge Add 33K resistors to J1,1 and J1,3 to J1,2 (ground)

10 Measurements Apply 2.5 Watts to RFin Connect RFout to an open ckt Note V FWD and V REV Adjust R3 or R4 to set V FWD = V REV Now measure V FWD and V REV For a 50, Ohm Load and a Short CKT Record Data on supplied form Does the data make sense?

11 Summary Meter measures voltages and currents SWR calculated Good example of Ferrite Transformers Simple circuit has many limitations Many examples on the WEB sma connector with jumper


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