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## Re: [Amps] AL 1500 P.O. Meter Function

 To: amps@contesting.com Re: [Amps] AL 1500 P.O. Meter Function Larry Benko Sun, 04 Oct 2009 23:11:45 -0600 mailto:amps@contesting.com>
 ```Joe, You are correct about trying to measure power based on voltage but in your example an SWR of 2:1 is the same as a reflection coefficient (Rho) of 0.333 meaning that the voltage on the line will be between 66.6% and 133.3% of the voltage on the line for a 1:1 SWR. This would mean than any power calculated from the voltage could be between 44.4% and 177.8% of the correct value. Not as bad as your numbers but still pretty far off. 73, Larry W0QE Joe Subich, W4TV wrote: > Based on the schematic of the amplifier, the PO function is > not a wattmeter but a simple capacitive voltage divider and > rectifier on the RF output. A circuit like that has no > directivity and is easily confused by reflected power and > common mode currents on the feedline. > > If you are concerned about accurate power measurements, > get a good wattmeter and use it in a matched circuit - > SWR = 1:1 - and use common mode chokes between the meter > and antenna. A capacitive voltage divider/rectifier will > only provide accurate readings with no reflected power to > "boost" or "buck" the voltage in the line. For example, > if the SWR is 2:1, "power" calculated by using a voltage > measurement can range from 25% to 400% of the actual > power depending on the distance to/from the antenna (load). > > 73, > > ... Joe, W4TV > > > _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ```
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