BLE advertising Frame with unexpected bits

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Nomnom_dialog
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BLE advertising Frame with unexpected bits

Hi all,

I've demodulated an advertisement frame from a DA14580 device using the rohde and schwarz CBT BLE tester. However, I'm having trouble understanding the frame structure. I've attached a picture (in pdf) showing part of the demodulated frame.

Why are there extra bits before the 1 byte preamble?
Is a carrier tone (indicated by arrow) absolutely necessary before the actual frame?

P.S. I was able to detect the DA14580 device just fine on a BLE sniffer. So, it's working fine.

Thank you all,
Ray

Device: 
MT_dialog
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Hi Nomnom_dialog,

Hi Nomnom_dialog,

Sometimes additional preamble is send, 8 bits is the minimum, so what you see perhaps is actually the preamble itself, regarding the 2-3us of carrier before the first bit is within our timing specs so there is no issue about this. What is more confusing is the Access address that is indicated by the graph that you have attached, if i try to decode the access address it don't really get the standard access address that an advertising message has to have. By spec this is 0x8E89BED6 and as far as i can tell you are getting something else.

Thanks MT_dialog

 

Nomnom_dialog
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Thank you for your insight. I

Thank you for your insight. I check over the demodulated signal, and compare it against another from a Beacon emulator app on an Ipad. They are a match, which should be 0x8E89BED6. Picture is attached.

An additional question, does the Beacon have to transmit on all three advertisement channels for a typical Android to pick up the signal? I would just like the beacon to transmit on channel 38.

Regards,
Ray

MT_dialog
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Hi Nomnom_dialog

Hi Nomnom_dialog

This is what the spec defines, that the advertising should happen in all three channels, but the android device should be able to track the advertising packet even if the device advertises on one channel, of course in heavy traffic locating one advertising packet to only one channel should be quite harder.

Thanks MT_dialog