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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>
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