Hi, all! Now I'm using USRP1 and RFX2400 d'board. In our project, we have to be able to reduce transmit power down to -40dBm. Please correct me if my approach is wrong. If we set tx_pga=0dB, the transmit power only depends on the level of signal. So, +/-32767 can give us maximum transmit power 17dBm because the maximum transmit power of RFX2400 is 17dBm. Since the power is a square of signal level, we can get -40dBm if we choose signal level +/-45 roughly. Am I right? -- View this message in context: http://www.nabble.com/RFX2400-Transmit-power-tp215... Sent from the GnuRadio mailing list archive at Nabble.com.
on 2009-01-21 03:38
on 2009-01-21 08:07
Hi Yong, I think with maximum signal levels of +/- 45 on the digital side your signal would be severely distorted due to quantization noise. Perhaps the easiest thing to do would be to put a mini-circuits attenuator inline with the SMA output of the RFX2400 board? Not sure if this will work for your application though. -Brian
on 2009-01-21 10:42
Yep, Brian's right. Doing what you propose would be equivalent to reducing the DAC to ~7bit and thus reducing signal-to-quantisation-noise-ratio by 54dB (!). You don't want that. Try subdev.set_gain(). You can see the available gain range with subdev.gain_range() (subdev is the object to access the subdevice, try usrp.selected_subdev() ). Perhaps that will help. MB
on 2009-01-21 18:24
Thanks all! As I know so far, RFX2400 doesn't have amplifier we can control. So set_gain() doesn't affect any transmit power. Right? Now I'm trying to control PGA gain on FPGA side, but I confused. AD9862 has pga which can be controled in range [0 ~ -20dB]. self.u.set_pga(0,-20) pga_gain = self.u.pga(0) print 'PGA gain ',pga_gain After running this code, I can see pga() returns -20. But transmit power is not changed. What's wrong? -- View this message in context: http://www.nabble.com/RFX2400-Transmit-power-tp215... Sent from the GnuRadio mailing list archive at Nabble.com.
on 2009-01-21 20:00
Yong J. Chang wrote: > You can use the PGA to reduce the gain on the RFX-series boards, but the problem is that the analog bias points for the quadrature modulator will change. You may be able to reduce 5-10 dB, but it may not operate well beyond that. The other way to change the output power is to reduce your digital level sent over the USB. Yes, this will reduce your dynamic range, so you won't want to do -40dBm this way, but 10 or 20 dB in reduction is fine. Matt