Presentation on theme: "SWR Meter Session 3 Learn about Transformers and SWR Meters"— Presentation transcript:
1 SWR Meter Session 3 Learn about Transformers and SWR Meters Forward Waves on Transmission LinesZL = Zo (Characteristic Impedance)IPort 1Port 2F+VTransmitterZLLoad-Zload = Zo (No reflected wave) Zo = 50 OhmsThere is only a forward wave. V=+IZoSWR = 1.0 (No standing Wave)
2 Reverse Waves on Transmission Lines ZL = Zo (Characteristic Impedance) SWR MeterReverse Waves on Transmission LinesZL = Zo (Characteristic Impedance)IPort 1Port 2R+VZLTransmitter-Here, ZL = ZoThere is only a reverse wave V=-IZoSWR = 1.0Current now reversed
3 Normally ZL not Equal to Zo Forward and Reverse Waves on the Line SWR MeterNormally ZL not Equal to ZoForward and Reverse Waves on the LineIPort 1Port 2+FRVTransmitterZLLoad-ZL not equal to ZoStanding Waves existForward wave reflects at load
4 SWR Meter Things to note in tests Forward wave power always greater than reverse wave powerForward wave power fixed for constant Tx PowerReverse wave power = 0 for ZL = ZoSWR 2:1 for ZL = 100 or 25 OhmsMeter actual measures Voltage and Current on the lineSWR must be found from VFWD and VREV on the board
5 Kits and Parts “meter” T1 samples current T2 samples voltage RF appears at DiodesDiodes act as detectorsVrev and Vfwd measuredSWR Calculated orMeters Calibrated
6 Marking the Transformers Two TransformersMark the red dots as shownThis is arbitraryI set the dots on the single turn
7 Marking the Transformers Set the other dots by inspectionThis is not arbitrary
9 SWR Meter Circuit…modified Current in T1Opposite directionfor Forward and ReverseR4, R3 balance the bridgeAdd 33K resistors to J1,1 and J1,3to J1,2 (ground)
10 Measurements Apply 2.5 Watts to RFin Connect RFout to an open ckt Note VFWD and VREVAdjust R3 or R4 to set VFWD= VREVNow measure VFWD and VREVFor a 50, Ohm Load anda Short CKTRecord Data on supplied formDoes the data make sense?
11 Summary Meter measures voltages and currents SWR calculated Good example of Ferrite TransformersSimple circuit has many limitationsMany examples on the WEBsma connector with jumper
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