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64332Re: [softrock40] Re: Combined Lite II for bandscope. Reduced gain resistor selection?

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  • Chris Wilson
    May 2, 2012
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      > --- In softrock40@yahoogroups.com, Chris Wilson <chris@...> wrote:
      >> 01/05/2012 23:59
      >> I am modifying, during the build phase, a Combined Lite II 40 metre kit
      >> to run on 9.01 MHz IF to hopefully provide a bandscope facility for my old
      >> Yaesu FT-902DM. A 12 MHz xtal, and the recommended caps for C3, 4, 11
      >> and 12, and winding the inductor L1 and transformer T1 to suit. the
      >> build notes suggest an alternative resistor pairing for R5 and R6 of
      >> 49.9 ohms for "lower gain". is it possible to tell at this stage if
      >> they should be used or the standard items of 10.0 ohms? Is there a way
      >> to measure the IF output level from the Yaesu and judge these resistor
      >> values accordingly? Thanks.

      >> Best Regards,
      >> Chris Wilson. M6DFV

      > Hi Chris, The IF output level of the '902 may be quite low and not
      > easily viewable with a scope. Also, you would need to be receiving a
      > signal leval that is as strong as the strongest you might encounter
      > when operating. And you would need to know the gains/losses from the
      > input (the '902 point-of-insertion)all the way thru to the I/Q outputs.
      > My opinion is to simply build the Rx with the 'standard' values in
      > the op amp circuit and see how it works. If you end up with too much
      > gain (overload of sound card), you can change the resistors as
      > appropriate or, since there is 100 Ohm on each I/Q output, just put
      > 100 Ohms (for example) from each ouput to ground (earth) to drop the level to 1/2.

      > 73, Sid W7QJQ
      > Okalhoma

      02/05/2012 09:38

      OK, that sounds good, will continue the build using the 10 ohm
      resistors for now. Thanks for the fast reply.

      Best Regards,
      Chris Wilson. M6DFV
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