FCC Band Edge Measurements at 2Mbit on Advertising Channels

[Kyle]

Greetings,

We are currently certifying a device to be compliant with FCC & IC rules in the US & Canada.  The upper band edge measurement is failing on advertising channel 39 (2480MHz) by 1.5dB when using the 2Mbit/s PHY.  My understanding of the Bluetooth 5 specification is that the only PHY used on the primary advertising channels (37, 38, and 39 / 2402MHz, 2426MHz, and 2480MHz, respectively) is 1Mbit/s.  In other words, we do not need to test the 2Mbit/s PHY at 2480MHz because it will never be used.  Is that correct?

Thank you,
Kyle

[AmbystomaLabs]

Since no one from Nordic responded, I'll give this a shot.

Per my read of the spec, you are correct that the BLE 5.0 spec has only 1Mbps operation on the primary advertising channels with both standard packets and LE coded packets. And, that 2Mbps is only used on the remaining channels (ie, 0 to 36).

Now that being said, absolutely every single test report for a BLE 5.0 device that I found tested both 1Mbps and 2Mbps at low, mid and high channels.

I think the discrepancy arises from the fact that the FCC different from other authorized bodies, doesn't really care about the protocol. You are just declaring that it is a digital transmission system, supporting GFSK at some data rates, in some ISM band on some channel scheme. You have to report your software version, but frankly that could be your internal rev of firmware or it could be a BLE spec and the FCC knows that it has very little control over the software once the device is approved.

Then you have the issue that the test lab is required to test the "worst case".  Well for this device that would be 2Mbps at low, mid and high.

I think you have a shot at getting your lab to not do 2Mbps testing on channels 37 and 39, but it will take some work on how the device is declared on the FCC 731 form and the ISED RSP forms. Also, you will have to come up with a lot of supporting documentation and likely your lab will get involved in calls with their TCB. They will have to do a little retesting too since there will be a different worst case for 1Mbps vs. 2Mbps operation.

I didn't go over the ISED rules to see if the guidance differed from the FCC's. But generally they have very similar rules which is why the two test plans are normally combined to save time&money.

If you go for a CE mark the process will be very different since ETSI combines protocol into their standards. So for ETSI you will be tested as a BLE device and not a generic GFSK device.