[hpsdr] Penny Question

robert halloway rhalloway at gmail.com
Fri Jun 12 13:34:31 PDT 2009


I have question that maybe the Penelope designers can help me with.
My nephew has a Penelope that he wants to use with a transverter that
requires about 10 mW drive.   If I read the AD9744 data sheet
correctly it is capable of 20 mA into a 50 ohm load.  With a 1:1
transformer this would be 20 mW I think.  I see that Penelope uses a
4:1 transformer and there is a 220 ohm resistor on the AD9744 side.
I'm guessing that this resistor establishes a 50 ohm impedance for the
following low pass filter?  If I replace transformer T3 with a 1:1
ratio transformer without a 50 ohm loading resistor (R17) is it
correct that I would get about 20 mW into a 50 ohm load?  With a 1:1
transformer and 50 ohms for R17 I should get 10 mW out into a 50 ohm
load?  Thanks, Robert.



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