3-input SDR with STEMlab 125-14 4-input?

[joansola]

Hello. I am new to redpitaya and a relative newby in SDR. I hope my question makes sense and that this is the right place to ask it.

I need to make a SDR application with 3 coherent channels for measuring 3D magnetic field at around 500kHz. I wonder if the STEMlab 125-14 4-input is good for me. My doubt relates the RF frontend. I would need automatic gain control for all inputs to handle the input level veriability. These AGCs should work in unison and report their gain downstream so that I can recover the original signal amplitudes for all channels. I assume the SDRlab has all these features (correct?), but it only has 2 channels, so not good for me. My question is: is the RF frontend of the 4-input STEMlab equivalent in this regard to the RF frontend of the SDRlab? Or should I consider other options for my application?

From the schematics of both systems I can see there are some differences, but I cannot conclude on a precise answer for my question.

Thanks!

[redpitaya]

Hello Joansola,

Thank you for writing on the forum. Sorry for the delay.

The analog frontend of the SDRlab 122-16 and STEMlab 125-14 are different:
- SDRlab has AC coupling, no anti-aliasing filter, and 50 Ohm input impedance.
- STEMlab 125-14 4-Input has DC coupling, aprox. 60 MHz anti-aliasing filter, and 1 Mohm input impedance.

Also, SDRlab has no "gain" setting. It just reports the exact signal value to the FPGA and later on the program. The 4-Input has a jumper immediately after the input, which indicates the input voltage range (LV == +-1 V, HV == +-20 V). And as long as the jumper setting is correctly supplied to the Red Pitaya, the gain measurement is already accounted for in the received measurements.

You can check the other differences here: https://redpitaya.readthedocs.io/en/lat ... ison-table

The only other thing that has an impact on the measurements is the calibration, but that just makes sure the measurements are correct.

Please let me know if I can help you with anything else. If you want a fastest response, please write to the support@redpitaya.com.

[joansola]

Hello. I replied on email as you suggested. Thank you!