On Fri, May 23, 2025 at 8:11 AM Nikos Balkanas <nbalka...@gmail.com>
wrote:
I have implemented the following calls for uhd_usrp_set_rx_lo_freq:
uhd_string_vector_handle names;
uhd_string_vector_make(&names);
if ((err = uhd_usrp_get_rx_lo_names(dev[channel], channel, &names)))
warn(log, "Failed to get lo names (%d). %s.\n", 0, FL, LN,
FN, err, uhdError(err));
if ((err = uhd_string_vector_size(names, &len)))
warn(log, "Failed to get lo names size (%d).
%s.\n",0,FL,LN,FN,err, uhdError(err));
if (!len)
{
error(log, "No lo names found on channel %d.\n", 0, FL, LN,
FN, channel);
uhd_string_vector_free(&names);
return(FAIL);
}
uhd_string_vector_free(&names);
The problem is that names always returns 0. This is not right for
my SBX-120, or any
daughterboard with a tuner:( This is what i can get from the API.
There are no LO examples.
I have seen lo_enable() in c++, but nothing exported to C. What am
I missing?
TIA
Nikos
On Fri, May 23, 2025 at 8:12 AM Nikos Balkanas
<nbalka...@gmail.com> wrote:
Thx Marcus,
For your fast and informative answers. Sorry it took me a
while to reply,
but I'm still trying to get:
tune_request(freq, lo_off)
to work in C.
My X310 has 2 SBX-120 boards. Using uhd 4.6.0 in Ubuntu 24.04.
True about the tuner. Much cheaper and easier to implement it
in analog.
I am using your FPGA image. Haven't touched it myself, yet.
So, the spike is pretty narrow to interfere with my signals,
but still messes my power calculations:(
I already implemented the integer frequency tuner and working
on the low oscillator offset.
If you have any pointers about it, feel free to advise.
LO is not part of the request_tuner_t struct. It is set
independently.
Is this the same LO in uhd_usrp_set_rx_lo_freq?
If this is the case I can modify it externally:)
BR
Nikos
On Fri, May 23, 2025 at 4:40 AM Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 2025-05-22 21:31, Nikos Balkanas wrote:
The spike is very clean to come from outside.
Must be from my X310. My tuner must be adding a signal to the
center frequency. The small artifact at 2 Ghz is probably
the tuner not
equilibrating fully.
I recently updated my FPGA image. Is that where the tuner
lives?
You haven't mentioned in this thread which daughtercard
you're using. RF front-ends that use complex-baseband
downconversion suffer from something called "DC-offset",
which produces a spike at 0Hz in the complex spectrum.
The radio block in the standard FPGAs has methods for
reducing this, unless you turn it off. This is a very very
*normal* thing for complex-baseband receiver chains.
If the algorithms are engaged and working, then there'll
still be a central spike, but *considerably* reduced, and
I find that
said spike is usually swamped by external signals, even
in radio astronomy.
The other method that people use is to use "offset
tuning". Where the tuner is tuned to a different RF
frequency, and the
DDC brings your signal of interest down to 0Hz.
https://files.ettus.com/manual/page_general.html#general_tuning
The "tuner" is an analog collection of components,
including an LO generator, and mixers. While it is
*controlled* through
the FPGA, it is an analog subsystem.
On Fri, May 23, 2025 at 3:19 AM Nikos Balkanas
<nbalka...@gmail.com> wrote:
Hello,
Whenever I look at my spectrum I always see an energy
spike at the center frequency.
In the first image you can see a spike at 2, but not
at 2.001 Ghz. In the next image,
at 2.001 Ghz you can see the energy spike at the
center frequency, but also a small
spike at 2 Ghz.
I have verified these results by both fosphor (OpenCL
fft) and fftw3f. Besides, if it were
an fft artifact, why is the spike at 2 Ghz still
visible after a few mins? These spikes
seem to be transient, but real. In that part of the
spectrum, you there is no traffic. Could it be
harmonics from my power supply? Problems with my
X-310? My transmitter
doing funny things (I have 2 boards and not enabling
my transmitter anywhere)?
Naming of images is freq_sr.jpg. All are in Mhz.
TIA
Nikos
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