Re: [Discuss-gnuradio] Question of tx_ampl range: [0, 1) or [0, 2^15/2) ?

[Josh Blum]

> In transmit_path.py ( ..->  packet_transmitter ->  Multiply Const ->  USRP
> Sink),  I see that the range of Multiply Const is [0, 1).
>
> However, in one of the GRC example usrp_tx_dpsk.grc (Random Source ->  DPSK2
> Mod ->  Multiply Const ->  USRP Sink), Multiply_Const = tx_ampl*p2p/2 , where
> p2p = 2^15.

There is a multiply_const(2**15) in the transmit_path example. See 
generic_usrp.py.

The gr-usrp sink always takes samples between +/-2**15. See the docs in 
the USRP sink block in GRC.

> Does anyone know why the Multiply_Const is set to tx_ampl*p2p/2 and what
> does p2p refer to?

It means peak to peak and the purpose is to scale the signal to the 
expected range of the usrp sink block. I believe that p2p should 
actually be 2**16 in this case, but it works.

-josh