Maximum I/Q signals frequency limit for TX

GNU Radio
1

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,

Regards,
Shaiful

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2

Shaiful wrote:

Unfortunately I can only transmit clean quadrature I/Q

transmit up to 44 MHz.
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

3

On Mon, Apr 23, 2007 at 09:42:46AM -0700, Matt E. wrote:

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.

As Matt mentions below, there are two things you can adjust: the RF
center frequency with -f RF_FREQ and the baseband data sample rate.
To increase the baseband sample rate, use the -i INTERP option. Try
-i 32. That’ll give you a baseband sample rate of 128M/32 = 4M
samples/s. The defaults give a baseband sample rate of 1MS/s which is
consistent with your report.

[eb@dee usrp]$ ./usrp_siggen.py --help
usage: usrp_siggen.py [options]

options:
-h, --help show this help message and exit
-T TX_SUBDEV_SPEC, --tx-subdev-spec=TX_SUBDEV_SPEC
select USRP Tx side A or B
-f RF_FREQ, --rf-freq=RF_FREQ
set RF center frequency to FREQ
-i INTERP, --interp=INTERP
set fgpa interpolation rate to INTERP
[default=64]
–sine generate a complex sinusoid [default]
–const generate a constant output
–gaussian generate Gaussian random output
–uniform generate Uniform random output
-w WAVEFORM_FREQ, --waveform-freq=WAVEFORM_FREQ
set waveform frequency to FREQ
[default=100000.0]
-a AMPL, --amplitude=AMPL
set waveform amplitude to AMPLITUDE
[default=16000.0]
-o OFFSET, --offset=OFFSET
set waveform offset to OFFSET [default=0]