Re: [Discuss-gnuradio] Maximum I/Q signals frequency limit for TX

[Matt Ettus]

Shaiful wrote:
> Hi guys,
>
> I'm trying to generate complex I/Q waveforms using
> this command (for 700 KHz):
>
> ./usrp_siggen.py -T A -w 700000 -f 0
>
> >From the mailing list, I've read that the USRP can
> transmit up to 44 MHz.  
>
> Unfortunately I can only transmit clean quadrature I/Q
> signal only up to 700 kHz.  Above the frequency, I'm
> starting to see two or more waveforms for each
> generated quadrature I/Q signals.
>
> If I increase the frequency further to 1 MHz, USRP
> only generate one signal from TX_A connector, there is
> no signal from TX_B connector.   Both TX_A and TX_B
> connectors are on daughter board of 'USRP Tx side A'
> as indicated by '-T' flag. FYI, I'm using LFTX
> daughter board not the Basic ones.
>
> If I transmit more than 1 MHz, the frequency is still
> cap at 1 MHz.
>
> Any idea what is happening and how to get higher
> frequency?
>
> Thanks,
>
>   
> >From the mailing list, I've read that the USRP can
> transmit up to 44 MHz.  
>
> Unfortunately I can only transmit clean quadrature I/Q
> signal only up to 700 kHz.  Above the frequency, I'm
> starting to see two or more waveforms for each
> generated quadrature I/Q signals.
>
> If I increase the frequency further to 1 MHz, USRP
> only generate one signal from TX_A connector, there is
> no signal from TX_B connector.   Both TX_A and TX_B
> connectors are on daughter board of 'USRP Tx side A'
> as indicated by '-T' flag. FYI, I'm using LFTX
> daughter board not the Basic ones.
>
> If I transmit more than 1 MHz, the frequency is still
> cap at 1 MHz.
>
> Any idea what is happening and how to get higher
> frequency?
>   


Yes.  the -w frequency is the baseband frequency.  To go higher you need 
to change the -f frequency which is the carrier frequency, or lower the 
interpolation rate.

Matt