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CC1125: PMR long range radio, Typical RX- and TX-Delay due to the digital signal processing

Hanspeter Oppliger
Prodigy 40 points
Part Number: CC1125

We are evaluating the usability of the CC1125 family for a PMR system, where the switching time between TX and RX is allowed to be max 3 ms. This means, the TX and RX "paths" must be much faster, to finally fulfill the max allowed switching time.

The frequency range is 400 - 470 MHz, the channel spacing is typically 12.5 kHz and so, the system is narrow bandwith. The baseband frequency is 3.1 kHz max. This means, that the RX-filter must be very narrow and in parallel the selection must be very good, to fulfill the ETSI 300 113 standard. Here the channel selectivity, the co-channel selectivity (both RX) and the adjacent channel power (TX) are critical. The RX sensitivity is -110 dBm max and the co-channel sensitivity shall be -12.0 dB.
The adjacent channel power is measured @ 8.25 kHz above/below the -6 dB point from the nominal carrier frequency. The limit is 60 dB below the transmitter power, without the need to be below 0.2 uW (-37 dBm). As we use in our system +27 dBm output power, the measured values shall be below - 33 dBm.


The questions are:

  • What is for such a narrow band TX system the delay throught the transmit chain, measured from the baseband input?
  • What is for such a narrow band RX system the delay through the receiver chain, measured to the baseband output?
  • Is the transeiver family capable to fulfill the adjacent channel power specification given in the ETSI 300 113, when used with 12.5 kHz channel spacing?
  • Is the transeiver family capable to fulfill the adjacent channel power specification given in the ETSI 300 113, when used with 6.25 kHz channel spacing?

 

We are looking forward to your reply and remain with our best regards,

Hanspeter Oppliger / WaveLab Engineering AG

P.S. Be aware, that I'm on holiday's till 15. October 2021, therefore I won't react on any enquiry or comment before - many thanks for your comprehension.

  • 0
    TI__Intellectual 1000 points

    Hi Hanspeter, sorry for the late reply. The EN 300 113 has changed a bit since we did the datasheet, so we're doing some new measurements now to see if we can pass the EN 300 113 spec. We also have some new register settings that we want to try out, but do not believe we will be able to pass everything in EN 300 113. The most challenging parameter is the spurious response rejection (basically the image frequency rejection, 70 dB) and the intermodulation (70 or 65 dB). We believe we can pass ACP and selectivity. Blocking at 1 MHz  (-23 dBm,  84 dB relative) will be more challenging, but lets see. If you have a relatively narrow frequency band you are targeting, then blocking can also be "helped" by a SAW filter - you're indicating you want to use a large frequency band, so a narrow SAW filter will not work.

    As you are also indicating, we're looking at lower bandwidths to (hopefully) pass the regulations, but that is probably not something that is attractive for a PMR solution?

    What is the lowest data rate that you can allow and do you have to pass all the EN 300 113 test cases?

    In terms of a delay, I am not really sure, but I do not believe this would be a problem for a PMR system (we have other customers for this application), but we naturally have high order digital filters to handle the selectivity for the device.