868 Mhz usage in U.S

[malik]

Hi,

We have been using Moteino 868 Mhz  successfully for past couple of years in U.K, now we need to ship some of our units to U.S for a product trial, but I am vaguely aware about FCC regulation about 915 Mhz is allowed instead of 868 ? Can somebody, kindly clear this for me, whether we can use our 868 Moteino based  designed in U.S or we need to change the module with 915 Mhz.

[joelucid]

You'll need to use 915 Mhz radios in the US. See https://www.semtech.com/images/promo/FCC_Part15_regulations_Semtech.pdf for the regulations of 915 Mhz. Felix actually sells 915 Mhz radios also for use in the 868 Mhz band so HW wise you likely don't need a change. You'll get improved performance since the 915 Mhz passive filters do degrade performance in the 868 Mhz band based on recent measurements I did.

Problem then is that the allowed TX power is very low (like -1 dBm or so) unless you use wide-band signals or frequency hopping. See http://www.semtech.com/wireless-rf/rf-transceivers/Boosting-ISM-Signal.pdf for details on wide-band signals.

If you want to use the full tx power of the rfm69hw frequency hopping is really the only solution.

Joe

[malik]

Thanks Joe.

I saw on Felix website the 915 MHz modules.
So do I need to replace my 868 ones with new 915 ones.
Or I can simply Change the firmware on 868 ones ?

[perky]

What Joe said. Not that simple unfortunately. In Europe the 868.0MHz to 868.6MHz sub-band can use 25mW with < 1% duty cycle which allows simple narrow band operation and hence good range. The FCC regulations don't use this approach, it's much more about spreading the RF power using wideband and using frequency hopping. If you use simple narrow band transmission you're basically shafted.
Mark.

[Felix]

Hi Malik,

Program your same modules (868/915mhz) with 915mhz settings, they will work just as well and will be OK for the US.
The ISM bands for EU is 868, for US is 915.

[perky]

Program your same modules (868/915mhz) with 915mhz settings, they will work just as well and will be OK for the US.
The ISM bands for EU is 868, for US is 915.

I think the OP said 'product trial'. They would need to meet FCC regulations if they were selling a product. It would work as you said (minor mismatching not withstanding), but those FCC regs are a PITA :-(
Mark.