Errors if oversample=1

General Discussion
1

I’m trying to generate a GFSK signal at 450Mhz using gnuradio-3.7.13-4-4build1 (Ubuntu 19.10 amd64) and a LimeSDR-mini.

If I set oversample=1, then I get the following errors. However, leaving oversample at “Default”, it works. So I have a work around, but the bug might be useful to someone.

LimeSuite and gr-limesdr were built from source (stable and master branches respectively).

Here is the gnuradio-companion log:

LimeSuite Sink (TX) info

##################
Connecting to device
##################
LimeSuite version: 19.04.0-gabf82140
gr-limesdr version: 2.1.4
##################
Device list:
Nr.:0 device:LimeSDR Mini, media=USB 3.0, module=FT601, addr=24607:1027, serial=1D53BA19C07646
##################
INFO: device_handler::open_device(): no serial number. Using first device in the list.
Use “LimeUtil --find” in terminal to find prefered device serial.
Reference clock 40.00 MHz
Using device: LimeSDR-Mini(1D53BA19C07646) GW: 1.28 FW: 6
##################

INFO: device_handler::enable_channels(): SISO CH0 set for device number 0.
INFO: device_handler::set_samp_rate(): set sampling rate: 0.072 MS/s.
INFO: device_handler::set_oversampling(): SetFrequencyCGEN(0.288 MHz) - cannot deliver requested frequency
Followed by a Python crash and libusb errors…

2

Hello robodan65,

That isn’t really a bug, a “Default” selection configures oversampling automatically, meaning it could be configured as high as 32.

3

Thanks for following up.

So you are saying there is an (undocumented) minimum sampling rate.

There might be a nicer way to communicate that than dumping core…

4

The smallest analogue filter for RX after the mixer is 1.4 MHz.
The smallest analogue filter for TX before the mixer is 2.4MHz.

There is a complex document that I use to find out the publicly documented LMS7002M registers that control the LMS7002M chip, plug “LMS7002M SPIRegs” into your search engine of choice (I’m not going to paste a direct link because there may be a later version of the document than the one I’m using - Version 01, Revision 18).

But you are right when someone demands a sample rate of 72 KSPS and wants to disable TSP decimation and force a 1.4 MHz of bandwidth to be folded into 72 kHz generating lots of aliases there should be a warning and crashing is the wrong kind of warning.

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