Topics

Frequency shift when Airspy HF "DSP library" enabled

David J Taylor
 

Context:
SDRangel 4.13.2
Device(s): Both AirSpy HF and HF+ discovery tested
Frequencies: 198 kHz 92.1 MHz 255.050 MHz

I notice that when the "DSP" button isn't pressed (i.e. the button is grey rather than orange) the receiver appears to shift 5 KHz low in frequency (the items on the spectrum display shift left, so likely the RX is high).

I don't know exactly what the DSP button does (OK, it toggles the DSP on or off!), but would you expect a frequency shift of an almost constant 5 kHz when it is disabled?

I've also noticed a tendency with recent versions (12 & 13.2) to close down unexpectedly when a new preset is selected while the RX is running.

Please let me know if there are any logs or screen-shots needed.

Thanks,
David GM8ARV
--
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor@...
Twitter: @gm8arv

Edouard Griffiths
 

Hello David,

this is due to linking with a more recent version of libairspyhf. Frequency correction is done via a library function (airspyhf_set_calibration). A lot of things are done in software with libairspyhf including precise LO correction via NCO. LO precise correction and other features like enhanced DC and IQ imbalance correction are optional and driven by activation of "DSP" feature which is linked to the "DSP" button in the UI that is active when background is orange.

For the other issue you mention that would require a core dump but I have no idea on how to get it and read it in Windows. However it is also necessary to know about the context and this is possible via the REST API and Swagger UI. When everything is set by default this is accessible via http://localhost:8091. Then you can click on Interactive Swagger UI documentation and access to Swagget UI.
  - GET /sdrangel gives general information about the SDRangel instance, the devices and channels attached.
  - GET /sdrangel/config lists all persistent values and presets. It can be large so you might be able to select only the preset in question.

In both cases clicking on "Try it out" and "execute" yields the JSON response in the "response body" box below.

With this information I can possibly try to reproduce the problem.

Brgds, Edouad.

Brgds,
Edouard. 

David J Taylor
 

Hello David,

this is due to linking with a more recent version of libairspyhf. Frequency correction is done via a library function (airspyhf_set_calibration). A lot of things are done in software with libairspyhf including precise LO correction via NCO. LO precise correction and other features like enhanced DC and IQ imbalance correction are optional and driven by activation of "DSP" feature which is linked to the "DSP" button in the UI that is active when background is orange.

For the other issue you mention that would require a core dump but I have no idea on how to get it and read it in Windows. However it is also necessary to know about the context and this is possible via the REST API and Swagger UI. When everything is set by default this is accessible via http://localhost:8091. Then you can click on Interactive Swagger UI documentation and access to Swagget UI.
- GET /sdrangel gives general information about the SDRangel instance, the devices and channels attached.
- GET /sdrangel/config lists all persistent values and presets. It can be large so you might be able to select only the preset in question.

In both cases clicking on "Try it out" and "execute" yields the JSON response in the "response body" box below.

With this information I can possibly try to reproduce the problem.

Brgds, Edouad.

Brgds,
Edouard.
==================================

Thanks, Edouard.

On the Airspy HF/Discovery, there should be no need for SDRangel to supply correction as the unit holds its calibration. What surprised me was that the shift was as much as it was (5 kHz), and that it was a constant shift almost independent of frequency. It's easy to live with.

OK on the crash. It /may/ be when a new preset is selected while the receiver is running. To start with, I'd like to know whether other Windows users are seeing this, or if it's just me!

73,
David GM8ARV
--
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-taylor@...
Twitter: @gm8arv