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## Re: [Discuss-gnuradio] Simple digital data transmitter

**From**: |
Tom Rondeau |

**Subject**: |
Re: [Discuss-gnuradio] Simple digital data transmitter |

**Date**: |
Thu, 13 May 2010 08:05:35 -0400 |

On Thu, May 13, 2010 at 1:18 AM, marcin_w <address@hidden> wrote:
>
>
>* Eric Blossom wrote:*
>*>*
>*> Your baseband sample rate is 100M/32 -> 3.125MS/s*
>*>*
>*> You're using 2 samples/symbol, thus your symbol rate is*
>*> 3.125MS/s / 2 -> 1.5625Msymbols/s*
>*> And since you're using DBPSK, you're getting 1 bit/symbol, thus your*
>*> raw over-the-air bit rate is 1.5625Mbit/s*
>*>*
>
>* Hi Eric, a quick question about this.*
>
>* According to:*
>* _pick_bitrate(bitrate, bits_per_symbol, samples_per_symbol, xrate,*
>* converter_rate, xrates, gen_info) in pick_bitrate.py*
>
>* when the samples per symbol and interpolation are given, then our bitrate*
>* can be determined straight away.*
>* i.e Bitrate = converter_rate / xrate / samples_per_symbol*
>
>* Is this correct though, in determining the bitrate for both dbpsk & dqpsk?*
>* For instance if we passed the_pick_bitrate() function an interpolation of*
>* 128 and Samples/symbol of 2, then according to the code, our bit rate for*
>* both dqpsk and dbpsk will be 500kbs.*
>
>* But according to what your saying:*
>* 1) for dbpsk*
>
>* if DAC rate = 128e6 Interpolation = 128 Samples/symbol = 2*
>* Bitrate = 128e6 / 128 / 2 = 500k*
>
>* 2) for dqpsk*
>
>* Using the same parameters*
>* Bitrate = 128e6 / 128 / 2 / 2bits per symbol = 256K*
>
>* Have i missed something here, or in the code?*
>
>* Regards,*
>
>* Marcin*
This does appear to be a bug. That calculation in pick_bitrate.py
should also be divided by bits_per_symbol.
Tom