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Help needed on RF scheme selection

Andrew Acree
Prodigy 60 points
Other Parts Discussed in Thread: CC1120, CC1101

Good evening, 

I performed a search here but I couldn't find anyone asking the same questions that I have, specifically regarding FCC information.

I am needing to select a communication scheme that will accomplish the following goals at a minimum:

  1. At least 1 mile range in line of sight, the more the better
  2. Use an unlicensed part of the RF spectrum
  3. Low enough power to avoid the need for the customer to possess an FCC license

We need to eliminate the need for a repeater, hence the 1-mile LOS range. The system will comprise of a single transmitter, and up to 100 receivers. There will always be one way communication, like a paging system. 

I'm really at a loss at to even which FCC band to be using for this application. Any information would be greatly appreciated!

Andrew Acree

  • 0
    TI__Mastermind 29570 points
    Please use the excel range sheet to predict your range : e2e.ti.com/.../375556

    What is the size of your product ?

    What is the size of your antenna ?

    When using the excel spread sheet, you can determine a practical range estimation by entering the output power, data-rate (sensitivity) , frequency and the height of the antennas above ground.
  • 0 in reply to RGW
    Prodigy 60 points

    I've tried using that spreadsheet but there are unknowns that I need to figure out first. One of which being the transmitting power. This is why I was asking what would be the recommended FCC spectrum to use.

    The transmitter will be wall powered, and fit within a 10" square base, with a maximum height of 8". The antenna length can be up to 24" and external. 

    The receiver will be battery powered with a base either circular (maximum 5" diameter) or rectangular (maximum dimension length of 8"). The antenna must be a pcb antenna. 

    There are a few unlicensed spectrums I've read about such as 315, 433, and 915MHz, but the guidelines are extremely confusing for someone who's never looked into them. This will be a commercial application. We need the devices to be FCC compliant (after certification) and use a spectrum and maximum transmit power that does not require the user to have an FCC license. But we need a mile range LOS. 

  • 0 in reply to Andrew Acree
    TI__Mastermind 29570 points
    Hi,

    For a large antenna, you will get range benefits from moving down from 868/915 MHz to 433 MHz. But for a limited size, the antenna efficiency will drop and this will effect the range.

    433 MHz is virtually a global frequency but with different regulations set around the world. Another advantage of the lower frequency is this is better at penetrating materials for any obstacles that might be in the line of sight. In Europe, according to the ERC 70-03 regulations you will be allowed to transmit 10 dBm of output power.

    868 MHz in mostly used in Europe and 915 MHz in the United States. This is basically the same BOM design since the two frequencies are so close.

    868 MHz you can send 14 dBm and even 27 dBm (within a 250 kHz BW).

    For the excel sheet estimations I would keep to 433 MHz or 868 MHz:

    Using 433 MHz, then use 10 dBm output and a Tx antenna gain of 2.1, and for the Rx antenna gain use -4 dB gain.

    For 868 MHz, use 14 dBm output, Tx antenna gain of 2.1, and -1 dB gain for the Rx antenna gain.

    This would give you a rough approximation of the expected ranges for the two frequencies.
  • 0 in reply to RGW
    Prodigy 60 points

    Richard,

    Thank you for the responses. I've been messing with the Range Estimation spreadsheet quite a bit. I've determined that based on the numbers you gave, there's less than a 1% difference in estimated range between the two scenarios.

    From what I've found so far, I want to use the CC1120 in both the transmitter and receiver. But I still have no idea which frequency to use.

    Is there another consideration I should be looking in to? You mentioned the antenna length might be an issue using my needed footprint for 433MHz. With everything else the same, should I just choose 868/915 simply because it'd be easier to package the antenna?

    Andrew

  • 0 in reply to Andrew Acree
    TI__Mastermind 29570 points

    If there is only 1% difference in the range expectations, then I would choose 868/915 MHz due to the antenna size on the receiver. For the same performance the Rx unit could be made smaller in comparison to a 433 MHz design.

    Which data rate will you be using ?

    Will the product be sold in Europe (868 MHz), United States (915 MHz) ?

    Regards,

        Richard

  • 0 in reply to RGW
    Prodigy 60 points

    Richard, 

    We will be using something <1kbps. The base station only needs to send 12-15 bytes total, and it will always be unidirectional communication. So there is no concern about transmission delay or total transmit time. The base station only initiates transmission on use and total transmit up-time will likely never exceed 5%. 

    As of right now, the product will be sold in the US only. European sales will be on the table for later and it would be very valuable to use the same board and antenna design for both if possible. Is it possible to have an antenna design optimized for both where the product needs only a software change between regions?

    Andrew

  • 0 in reply to Andrew Acree
    TI__Mastermind 29570 points
    Hi,

    If you use the DN024 antenna then this will handle both 868 MHz and 915 MHz frequency bands.

    Regards,
    Richard
  • 0 in reply to RGW
    Prodigy 60 points

    Richard, 

    Thank you for the information. I would like to know what you think about the following hardware selection and my assumptions about the corresponding functionality. 

    Since the base station transmits only and we would like for the antenna to be an attachable unit like what comes in the development kit for 915MHz, am I correct in assuming that if I use a Value-Line wireless mcu such as the CC430 or CC111x, I can simply set the transmit power to 14dB and get maximum performance?

    Likewise, since the receiver units will only be receiving and never transmitting, to maximize range with a PCB antenna like the DN024 I can use a performance line unit like the CC1120? 

    My main assumption here is that the sensitivity of the transmitting chip is irrelevant and the sensitivity of the receiving chip is what matters. Is this correct?

    Also, as I have never used either wireless MCUs (CC430 or CC111x), what is the deciding factor between the two? They both look like they would do exactly what I need them to and more. The base station is what would use the wireless mcu if my previous assumptions hold true. The base station simply needs to transmit, control a 4 digit display (LCD or LED doesn't matter), and take input from a keypad. Is either chip easier to develop?

    Thank you,

    Andrew

  • 0 in reply to Andrew Acree
    Prodigy 60 points

    Richard, 

    Any input on my previous questions? 

    Thank you,

    Andrew

  • 0 in reply to Andrew Acree
    TI__Guru**** 317180 points
    CC430 or CC1110 both are based on the CC1101 radio. Which of them you should use is then mostly dependent on which type of MCU core (MSP430 or 8051) you like the most. If you want to control a display I would look into CC430 since some of them has a built-in LCD driver.

    Q: My main assumption here is that the sensitivity of the transmitting chip is irrelevant and the sensitivity of the receiving chip is what matters. Is this correct?
    A: Yes