How to check if the FiPy LTE radio is damaged or not



  • I have by a mistake run LTE CAT-M1 example script without moving the antenna from the LoRa/Sigfox antenna U.FL connector to the LTE antenna connector. After discovering this I connected the LTE antenna to the LTE U.FL connector, but now the FiPy will not attache to the radio access network. Prior to this and without LTE antenna I, strangely, observed that the FiPy did actually connect to the radio access network, but first after 5 to 10 minutes of waiting.
    Now it seems to be "dead".

    Is there a way to check if the LTE radio is damaged or not, ref https://docs.pycom.io/gettingstarted/connection/fipy.html ?



  • @devodog You're welcome. ;o) private repo link


  • Global Moderator

    @devodog Sorry no. I only kept copies of the NB-IoT firmware. But Pycom should have them.



  • @robert-hh
    As said earlier, the modem seems dead after upgrading the modem firmware. As a last attempt, I would like to downgrade the modem firmware to the one that produced some sensible reception readings, but I can't find 39529 (CATM1-39529.dup) for Sequans modem. Do you know if this is available from some repository?


  • Global Moderator

    @devodog You should also be able to break a running code with Ctrl-C or to perform a safe boot with Ctrl-F. Also, pulling P2 low during reser puts the device into firmware update mode, at which state one erase the flash, if things go totally haywire.
    After creating the lte object, AT+CSQ also returns 99,99. I have to switch on the radio first with AT+CFUN=1, and then after a few moments AT+CSQ returns a good value.
    No having a reasonable response to AT+CSQ looks bad. In my failed attempts, this was the only thing that worked.



  • @robert-hh
    As you said - "...it is always possible to recover the firmware on a xxPy device..", but not necessarily strait forward. I had to use the P12-to-3.3v wire-strap (for not longer than 3 sec.) to safe boot the device to disable boot.py and main.py, and got the python prompt in a putty console. Long story short: I now have CATM1-41065 firmware on the modem, but it does not attach to the radio access network. The coverage should be good since I have 3 "base stations" in the near vicinity (250 - 300 meter) of my home.

    Another observation is that the modem now seems not to receive any signal when i execute the 'AT+CSQ' command - it shows only 99,99 which is no useful information. When I was using the CATM1-39529, the modem produced an output of 23,99 - 27,99, which means some sensible signal strength.

    As I have understood the specifications for the radio interface between the User Equipment (UE) interface and e-NodeB (eNB), the UE will detect the sync signal (periodic) from the eNB, and based on the received signal strength and other information in this signal, the UE will issue a attache message with proper power and timing. The attach request til then be received by the eNB and forwarded to Mobile Management Entity (MME) and this will decide whether to accept the request or not. So, the FiPy modem would start to listen for the eNB "beacon" and if not good enough, keep listening - thereby waiting forever for an acceptable physical bearer channel.

    NOTE! this is what I have extracted from various resources on the net and is absolutely up for discussion and serious review. I would surly appreciate any corrections of my understanding.


  • Global Moderator

    @devodog If the pymakr console fails, try a dedicated terminal emulation program like putty. For putty, set flow control off, speed to 115200 baud. When you reset the device via reset button, you should see at least the reset & boot messages. It is always possible to recover the firmware on a xxPy device, unless it was encrypted.

    Windows has the habit of changing COM port numbers when you plug the device into a different USB port, which is kind of confusing. You can tell the port number by looking into the device manager.
    I cannot tell you the procedure of device attachment. I found the 3GPP documents barely readable.



  • @robert-hh
    I just tested your idea on measuring the output radiation from the external antenna, but could not detect any significant signal - most noise of some kind. This leads to another question, which is: What is the procedure/protocol for LTE Base Station to device attachment. I have dived into the 3GPP specs (TS 36.213 Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures) and try to interpret the information there.
    Anyways, I also saw that my firmware is two versions old so I tried to upgrade according to the pycom docs. This failed and the FiPy device is stuck in an application running a never ending loop and I'm not able to connect to the device in any way now - tried most stuff but I'm left with either:
    Connecting to COM6...
    Connection error: Error: timeout
    or:
    Connecting to COM6...

    Failed to connect (Error: Port is not open). Click here to try again.
    So for now I'm concentrating on getting in touch with the device through the pymakr console.


  • Global Moderator

    @devodog The pisoscope is sufficient. It is important to have the capacitive load as small as possible, so use a 10:1 test probe.
    The blie heartbeat is AFAIK not related to any LTE RF activity. As far as I recalled, there is only a short burst some time after reset.
    https://forum.pycom.io/topic/3549/important-update-regarding-lte-modem-updates/64



  • @robert-hh
    This was actually a good idea. I have a picoscope (100MHz) for use with a PC, an I will try your suggestion.
    I would expect the modem transmitter will send packet-bursts periodically - a wild guess would be like every 3800 ms since this is the periodicity for the blue LED on the FiPy board. So this transmit burst might be detected by the diode as you said.
    Thanks a lot for your responds.


  • Global Moderator

    @devodog If you have an oscilloscope, even low bandwidth, you can at least tell if there is some RF transmission. Use a high impedance tip (10:1, 10 MOhm), and a small signal diode as receiving antenna (1n4148 or better 1N5711). The Diode will rectify the RF, So you can see just a slow pulse, level several 100 mV. If you see pulses, you know at least that the device is transmitting. If you do not see anything, it proves nothing. Possible causes: a) the signal may be too small, b) the (diode-)antenna is misaligned, .....,

    WP_20180907_10_01_27_Pro.jpg



  • Currently I'm using a type of internal antenna from WIESON (seems to be similar to http://www.wieson.com/products-view.php?sn=279) which is designed to ~900MHz band.
    But I really would like to know if there is any way to know if the radio module in the FiPy is damaged or not without having advanced spectrum analyzer.


  • Global Moderator

    @devodog Unless you know that you are using a LTE band at about 900 MHz, you should use the LTE antenna. The Pycom SigFox/Lora antenna is designed for ~900 MHz, with acceptable parameters between 800 and 1000 MHz. If you are using a 700MHz or 1800MHz band, then the LoRa antenna will hardly be better then using no antenna at all, which both has to be avoided.
    So: fist step is to connect a proper antenna.


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