Dan, Any chance you can attach those pictures in a different way and resend, I 
couldn't find a way to view them and I'm curious to see them.
-Ian

On Jun 11, 2013, at 10:12 PM, Dan CaJacob <dan.caja...@gmail.com> wrote:

> There are two parameters that will affect your TX power: digital amplitude 
> and RF gain.  The digital amplitude sets the amplitude of your signal going 
> into the DAC.  UHD expects a signal between 0 and 1.0, but to keep your 
> output nice and linear, keep your signal amplitude belw 0.2.  Conversely, 
> 0.02 seems pretty low.  RF gain is applied in the aughtercard once your 
> signal has been up converted.  My practice is to keep the signal amplitude at 
> 0.2 max amplitude, then adjust RF gain to control power.  You'll end up 
> getting less than the max rated power output (e.g. 20 dBm for WBX, but you'll 
> have a clean RF signal.
> 
> I very recently characterized a WBX across the full range of amplitude and 
> gain settings.  Here's the result.  Note that the non linearity belw a gain 
> of about -10 dB is due to the signal power being belw the bottom range of the 
> power sensor.
> 
> 
> And here's a plot for just the 0.2 amplitude curve.
> 
> 
> 
> 
> On Tuesday, June 11, 2013, yeran wrote:
> Dear all,
> 
> I am doing channel estimation in gnu radio narrow-band. I'm collecting data 
> at the receiver side after the time_recov block. It has been through the  
> gr.firdes.root_raised_cosine in the time_recov. But the plot I get is as the 
> figures in the attachment. It looks like the fluctuation of the channel 
> amplitude has some pattern, it looks like signal pulse shaping in there. But 
> doesn't the gr.firdes.root_raised_cosine works as the rrc matched filter, and 
> already take off the pulse shaping?
> 
> Also, when I do experiment, I found out something strange. According to my 
> understanding, the --tx-amplitude on the transmitter benchmark sets the 
> transmission power. So the bigger the amplitude is, the better performance it 
> should be, since the SNR will be bigger. But in actual experiment, it is 
> totally the opposite way! The amplitude of 0.02, or even 0.002 works better 
> than the default 0.25. Has anyone come across the same problems?
> 
> Highly appreciate if anyone can give me some suggestions on this! Thanks in 
> advance!!
> 
> Ada
>  <rrc.png>  
> 
> 
> -- 
> Very Respectfully,
> 
> Dan CaJacob
> 
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