According to the AD8047 datasheet, the output voltage range is +/- 3 volts into a 150 ohm load. That works out I believe to 30 milli-watts of output. So it should be able to sink sufficient current to do better than what I'm observing...
On Wednesday, July 30, 2014 4:22 PM, Marcus D. Leech <mle...@ripnet.com> wrote: On 07/30/2014 04:14 PM, emat...@yahoo.com wrote: > Hello- > > I have attempted to increase the output power from my Rev 2.2 LFTX as per > instructions from Matt Ettus on this list dated Aug 3 2013 in which he > suggests reducing the values of resistors R3 and R5, but I am seeing a > clipped output at peak values much less than expected. > > Using the ettus.com LFTX schematic as a guide, I left the resistors on the > board untouched, but soldered wires to either side of R3 and R5 to add > additional resistors in parallel. My first attempt was with resistors of > value 220 ohms; I figured this would about halve the value at R3 and R5 which > are originally 225 ohms. I do see some increase in output power, but very > minimal. Specifically, whereas before I was observing 1 V P-P, or about 2.5 > milli-watts on an oscilloscope that is 50-ohm DC coupled, I am now seeing > 1.34 V P-P, or about 4.6 milli-watts with a 1 kHz sine-wave. To obtain this > without clipping I had to reduce the amplitude on the USRP sink block from 1 > to about .77, othwerwise the tops of the sinusoids flatten anywhere above the > 1.34 V P-P level. So I appear to be saturated. > > I am using a USRP1 Rev. 3. I verified that the LFTX output op-amp in > question is supplied with +/- 3.3 volts, so I don't see why it is clipping at > half of this. > > I am hoping to use the LFTX in an HF Ham radio application. I have > mini-circuits ZHL-1A TX pre-amplifier for this purpose, but was hoping to > obtain a little more output from the LFTX than I am currently getting to > drive the ZHL-1A. Any thoughts? > > Thanks! > > Eric > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio I would look at the datasheet for the driver amp. But +6dBm is pretty-close to the max output of the DAC as I recall, so you might be better to just put an interstitial amplifier in place. _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio