On Thu, Jul 30, 2015 at 1:37 AM, Jeon <sjeon87+gnura...@gmail.com> wrote:
> I am building a communication system which uses light. For the system, > I've buiult a custom analog circuit and connected it to LFRX with > SMA-BNC-Alligator clip. > > A simple dry run gives the following: > <snip> As you can see, data is transmitted with on off keying. > (Please ignore some ripples and fluctuation, it's due to 60 Hz fluorscent > light interference. I'll fix it later.) > > I wonder that such input range (+- 50 mV) is quite acceptable for GNU > Radio to manipulate. > > Since it's my first time to physically implement a communication system, I > only have mathematical and theoretical knowledge, but have little > experience and sense about dBm, rx sensitivity and so. > > But as I can see the waveform not so bad, I think I can manipulate it by > equalizing or something... > > PS: In addition, that 60 Hz interference, would it be better if I filter > out that at the analog circuit with high pass filter? Or is it just ok to > use high pass filter block in GNU Radio. I think the former is better to > reduce the computational cost of GNU Radio. And it is more proper to filter > out before it passes through the ADC... > > Regards, > Jeon. > Jeon, This is pretty cool. I'll leave the answer about the 50 mV to Marcus who has already replied. One thing to add is that you'll want to take your signal up to about +/-1 in the floating point world (whatever that means in real voltage), which you'll do using an AGC block. This block will just scale the signal (and the noise). I think that signal looks really clean. The fluctuations are evident, but you know, at least partly, where they are coming from. Given that you have a known source of interference that will likely be present in almost any situation you are interested in, I would suggest a hardware filter. You'll likely need other filtering later on for different effects and environments, and this is where the digital filter would be useful. Tom
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