Upconversion problem

GNU Radio
1

I’m using a FLex900 daughterboard with the usrp. I used the
usrp_siggen.sh script from the /gr-usrp/apps folder.
I wanted a sinusoidal carrier(no modulation) at 915Mhz. However after
running the code I observe max. power at 920Mhz in the spectrum analyzer
and a small peak at 915Mhz.

I am not clear how the wfreq(waveform freq) parameter in the foll. line
of code:
/* Set up the signal source */
siggen = gr_make_sig_source_c(input_rate, GR_SIN_WAVE, wfreq, amp);

affects the output.

The output that was displayed was:

which: 0
interp: 128
rf_freq: 9.15e+08
amp: 5.000000
nsamples: 0
Subdevice name is Flex 900 Tx MIMO B
Subdevice freq range: (8e+08, 1e+09)
mux: 0x000098
usrp->dac_freq(): 128000000
usrp->interp_rate(): 128
baseband rate: 1e+06
target_freq: 915000000.000000
ok: true
r.baseband_freq: 920000000.000000
r.dxc_freq: -5000000.000000
r.residual_freq: 0.000000
r.inverted: 0

I dont know if I’m setting incorrect values or using a wrong approach.
Please help me out.

Thanks
-Rush

2

On Wed, Jul 15, 2009 at 5:59 PM, [email protected] wrote:

The output that was displayed was:
usrp->interp_rate(): 128
baseband rate: 1e+06
target_freq: 915000000.000000
ok: true
r.baseband_freq: 920000000.000000
r.dxc_freq: -5000000.000000
r.residual_freq: 0.000000
r.inverted: 0

What I think is happening is you are sending out a tone at 5MHz. What
is the value of wfreq?

If you send out strictly DC when you upconvert to 915MHz, you will see
something at 915MHz. Positive frequencies shift the carrier higher,
negative frequencies shift the carrier lower.

I dont know if I’m setting incorrect values or using a wrong approach. Please help me out.

Hope this helps.

Brian