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Published byNathan Barker Modified over 4 years ago

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**SWR Meter Session 3 Learn about Transformers and SWR Meters**

Forward Waves on Transmission Lines ZL = Zo (Characteristic Impedance) I Port 1 Port 2 F + V Transmitter ZL Load - Zload = Zo (No reflected wave) Zo = 50 Ohms There is only a forward wave. V=+IZo SWR = 1.0 (No standing Wave)

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**Reverse Waves on Transmission Lines ZL = Zo (Characteristic Impedance)**

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

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**Normally ZL not Equal to Zo Forward and Reverse Waves on the Line**

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

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**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 ZL = Zo SWR 2:1 for ZL = 100 or 25 Ohms Meter actual measures Voltage and Current on the line SWR must be found from VFWD and VREV on the board

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**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

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**Marking the Transformers**

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

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**Marking the Transformers**

Set the other dots by inspection This is not arbitrary

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**Ideal Transformers N1=N2 Identical Windings Lenz and Faraday**

B1 Lossless 1 mA B1+B2 =0 1 mA ZL Lenz B2

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**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)

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**Measurements Apply 2.5 Watts to RFin Connect RFout to an open ckt**

Note VFWD and VREV Adjust R3 or R4 to set VFWD= VREV Now measure VFWD and VREV For a 50, Ohm Load and a Short CKT Record Data on supplied form Does the data make sense?

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**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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