Re: [Discuss-gnuradio] Data Types In GNU Radio

[Tom Rondeau]

Fatima Af wrote:
> Hi,
>
> I am working on a project on Cognitive radios. I want to achieve
> real-time transmission n reception of audio between two USRP boards. The
> biggest problems i am facing are in designing the flow graphs because of
> data type mis matches. For example i am taking the audio input from
> microphone and its Float type but blocks like modulation and
> chunks_to_symbols do not accept float type data. I have tried to use the
> float_to_char bloack to accomplish the necessary conversion but
> unfortunately it didnt work.
>   
> Another question is "Are the float_to_char and char_to_float bloacks bot
> exactly reciprocal of each other??? (coz after passing through both
> these bloacks the original float signal wasnt recovered) Similar is the
> case with float_to_short and short_to_float blocks..."
>
> Kindly guide me how i should get rid of this data type issue coz alot of
> my time is getting wasted just in resolving it..
>
> Looking forward to your help...
>
> Regards
>   

You probably need to adjust for the difference in dynamic range. Float's 
give you 32-bits and chars are only 8-bits, so you will likely be 
clipping a lot. You need to understand the data types to convert from 
the floating-point representation to a PCM representation that you can 
then split into chunks for the modulators to handle.

I you want to know if the two blocks are reciprocals or each other, you 
can always look at the code. Neither of these blocks are very complicated.

Tom