64332Re: [softrock40] Re: Combined Lite II for bandscope. Reduced gain resistor selection?
- May 2, 2012
> --- In firstname.lastname@example.org, 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
OK, that sounds good, will continue the build using the 10 ohm
resistors for now. Thanks for the fast reply.
Chris Wilson. M6DFV
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