Low sample rate in tx limited to 100ks?

I am using GNU RADIO on WINDOWS 10 to do amateur radio DVB-S2 emission experiments with the limeSDR mini
I am not a programmer.
I installed PothosSDR 2021 07 25 vc16-x64 with the Lime suite
I am using the Soapy Custom or Soapy lime Sink or Osmocom Sink module.
We are doing very low bit rate testing in DVBS2 emission.

With SOAPY modules the sample rate is limited to 100,000cps
With the Osmcom sink module I can go down to 40000cps with the device argument “driver = lime, soapy = 0” but the constellation and the results for all flow rates are much worse (m e r)
While it is the same driver
Is it a problem with the limitation of the driver or the GNU Radio module ?
Is there a way to “force” the sampling frequency lower for the SOAPY sink module ?

Thanks for your help.

The smallest analogue TX low pass filter is 1.8 MHz, you can see where that is within the overall LMS7002M functional block diagram.

Which in my mind would typically correspond to a minimum TX sample rate of about 2 MSPS, but that is not to say that you could not transmit a signal that is only using 10Hz of bandwidth anywhere within that 2MHz (Look into the gnuradio Frequency Xlating FIR Filter block I suspect that might help you).

Lowest sample rate I try was 192KHz but it was not with GNU radio. Small sample rates are for narrow band modulation like CW, SSB, AM, NFM… What you need is sample rate at least twice the DVB-S2 signal width.

In our amateur radio experiments we manage to transmit in DVB-S2 with a very narrow bandwidth.
The smallest to transmit a video with sound is 36kHz to transmit a DVB-S2 16APSK signal at 25 kS/s
In the configuration of the DVBS2 examples in GNURadio we therefore need a sample_rate = symbol_rate * 2 or 50kHz or even 40kHz in some tests.
With the Osmocom sink module and the Soapy driver there is no this limitation but the signal is not “clean”. Maybe there is no IQ balance correction?
With the Soapy LimeSDR sink module, the signal is perfect (constellation) but limited to 100kHz

Why don’t you request an arbitrary sample rate higher than required (say 1.2 Msps) and them resample your DVB-S2 signal to that particular sample rate?

I do not understand how the Soapy Sink module works in DVB-S2 but with a larger sample rate the phase quadrature modulation does not work (checked with an oscilloscope)
However, I have resolved the malfunction of the osmocom sink module.
This was due to too much gain on an intermediate stage, so I can use it because we can go lower in sample rate
Thanks for your help.