LOGARITHMIC_WATTMETER

Published:2009/6/26 2:59:00 Author:Jessie | From:SeekIC

Single meter scale covers 1-1000W, with equally spaced divisions for 1,10,100,and 1000. This log scale makes it possible to measure very low reflected powers and very high forward powers simultaneously with same percentage accuracy. Basis of operation is that voltage dropped across forward-biased 1N40C2 silicon PN junction diode is proportional to logarithm of cur rent through it. For 50-ohm line, use 220 for R2 and 27 for R3 and R4. For 75 ohm Iine, coffesponding values are 180 and 33. Detectordiodes are point-contact germanium rated at 80 PIV. Article gives construction details. Ground coax braid at one end only. Ferrite ring is 0.5-inch Mullard FX1596 or equivalent.-P.G.Martin, Some Directional Wattmeters and a Novel SWR Meter, 73Magazine,Aug.1974,p 17,19-21,23-24,and 26.



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