[hpsdr] Penny Question

[Graham / KE9H]

Robert:

I would recommend purchasing or building a 10 dB pad, and setting the output
of Penny to 0.1 Watts (100 mW) so that the output of the pad would be
the 10 mW you need.  You can build one for three resistors and two 
connectors,
or buy one on eBay for about $10.

If you changed the Penny circuitry as you describe below, you would 
defeat the
closed loop power control, so you would also have to go into the 
software, too.

And 20 mA is the peak output of the data converter.  Divide by
1.4 for the RMS value used for calculating power.  After doing all the
math, the maximum you could get out of the data converter directly is 
about 2 mW,
before filter losses.

--- Graham / KE9H

==

robert halloway wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> 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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