Daq_chain_config.ini sample_rate=500k but receiving ~2.4MHz - Config not applied?

1

Hi KrakenSDR community,

I’ve searched the forum and found similar issues with low sample rates (like the 250kHz calibration problem), but my situation seems different.

My Setup:

  • KrakenSDR with latest Heimdall DAQ firmware

  • Raspberry Pi 4

  • GNU Radio on Ubuntu VM receiving via TCP port 5050

Issue:

Despite setting sample_rate = 500000 in daq_chain_config.ini, I’m consistently receiving ~2.0-2.4MHz worth of data in GNU Radio.

My config:

ini

[daq]

sample_rate = 500000

decimation_ratio = 1

center_freq = 147000000

[data_interface]

out_data_iface_type = eth

What I’ve verified:

  • Config file is being read (center_freq changes work)

  • Heimdall starts without errors

  • No GNU Radio decimation/interpolation blocks

  • Measured actual sample rate in Python embedded block

Specific questions:

  1. Does RTL-SDR hardware have minimum sample rate limitations that override config?

  2. Should I expect decimation to happen at DAQ level vs DSP level (as mentioned in the 250kHz thread)?

  3. Which log files should I check to see what sample rate RTL-DAQ actually sets?

I suspect the config isn’t being applied at the hardware level, but would appreciate guidance on debugging this.

Thanks!

2

Hm it should work at the lower sample rate, but if it’s not you could also try increasing the DAQ side decimation.

2.4 / 5 should get you to 480 kHz which would be near equivalent to setting the sample rate to 500 kHz.