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Re: Ensemble RXTX PA Standing Current Question

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  • g8voip
    Hi Paul, The difference probably is due to the characteristics of the two FETs being used or minor differences in the source or gate resistor values. You could
    Message 1 of 2 , Aug 30 11:20 PM
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      Hi Paul,

      The difference probably is due to the characteristics of the two FETs being used or minor differences in the source or gate resistor values.

      You could remove R46 & R47 and R48 & R49 to check their values are the same, or replace the BS170 FETs. Usually if they come from the same batch the characteristics are pretty similar.

      There might be some slight degradation in the RF output quality, but I suspect in practice you would not really notice it if you stick to using the Ensemble by itself. If you intend to add an amplifier after it, then probably more important to make sure the drive signal is as clean as possible.

      73, Bob G8VOI






      --- In softrock40@yahoogroups.com, "wnpauls" <wnpauls@...> wrote:
      >
      > In the Driver/PA Testing the current draw is normal (25.6 ma and 121.5 ma with PTT activated).
      >
      > The PA Standing Current is a problem ?
      > Voltage across R48 si 54.5 mV.
      > Voltage across R49 si 48.8 mV.
      >
      > The difference is a bit more than 10% of the average.
      >
      > How can I adjust the balance of these PA standing currents?
      >
      >
      > The forward bias is 2.65 volts a bit high but consistent with Robby's measurement.
      >
      > thanks,
      > Paul K0ZYV
      >
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