Having some anomalies with and questions about the ST25RU3993eval.

[DBurt.1]

1. I have found on one day I get good performance and read range from the unit, but I can come in on the next day and only be able to read an inch or so with the same settings. Today it is working reasonably well again. Can anyone explain this?
2. I need to read two different tags both in range. It seems the larger tag always kills the ability to read the smaller tag. I assume this is because it gets swamped by a larger return signal from the larger tag? Any way around this? Or am I misunderstanding what might be happening here?
3. I'm going to be extracting what I think we need from the eval board design. (Hopefully no ext power amp or signal switches, etc.). Is there any chance I can get away with a fixed tuning since all our implementations will be the same and the tags will be of fixed type and location? I assume I can optimize with the eval board and just save my settings and the tuning table to use as fixed parameters.
4. Are there any guidelines that help with deciding how to set up all the various parameters for best performance? (i.e. output level, receive gain, adaptivity or AGC?

Lastly, are there any UHF RFID experts here who could consult on a project and maybe help us avoid some pitfalls?

Thanks.

[Cedric Dalban · Accepted solution]

Hello DBurt,

some few comments related to your questions.

1) The reader and tags are really sensitive to tuning (cf Application note: AN5532, https://www.st.com/content/st_com/en/products/nfc/st25-nfc-rfid-tags-readers/st25-nfc-rfid-readers/st25-uhf-readers/st25ru3993.html#resource).

I assume your performance results from one day to another are linked to tuning.

Please ensure you pre-tune the reader before starting your inventories.

Reader Suite (RS) provide a dedicated tab for it (Reader Settings->Tuning), you can even save the tuning and other settings in a text file (on main window, right click on "ST25RU3993 Reader" and "Save Reader Settings") and reload it.

If you are using STUHFL API, some example code is provided with releases for proper tuning, SLOW method is the most efficient. 

Please ensure as well the output level, receive gain, sensitivity and Q are identically set from test set to another.

2) The UHF technology is relatively protected against return signal swamping each other. Nevertheless, if the smallest tag is directly located behind the biggest, the antenna of biggest may be seen by the smallest as a shield and it becomes untuned, this explaining smallest is never answering.

3) As mentioned above, the RS allows to do the appropriate tuning and save the result (on main window, right click on "ST25RU3993 Reader" and "Save Reader Settings"). The generated file can be used to reload the tuning values in RS.

This file is a text file, if you are using the STUHFL API, the file can be used as well to see and reuse the tuning parameters with STUHFL API (API: SetTuningTableEntry(), demo code in demo_resetFreqsTuning()).

4) UHF system really depends on the overall environment conditions, it is difficult to provide guidelines working for all conditions. Anyway, the RS helps playing with the various parameters and get the best configuration for the current conditions.

Regards,

Cedric.

[DBurt.1]

Thanks for pointing out the save reader settings option. I was hoping I could do that but had only seen the antenna settings save function.

I've been using adaptive sensitivity, AGC mode and adaptive Q. Setting target as A only and S1 session helped a fair amount with multi tag reading.