Apple

I have tried several units inside the RF box, and the iPod reads values in a 4 dB range, as compared with 25 dB lower for a unit with no antenna, so I think the plan is workable in that respect. Multiple runs with one unit yielded values in a 3 dB range, which is pretty good too. Both of these tests were using the readRSSI / peripheralDidUpdateRSSI pair, which seemed to work a lot better than the didDiscoverPeripheral measurement in open air.

I had hoped to be able to lower my acceptance threshold to somewhere in the 10 to 15 dB range below optimal, to detect defective antennas, and not just missing the missing ones at 25 dB down. It is a bit late for me to give up on this now. Also, does anyone have a answer to that second question: if the measurement is instantaneous?

Jeff

From: András Kövi [mailto:email@hidden]
Sent: Tuesday, February 26, 2013 5:38 AM
To: Jeff Hosack
Cc: email@hidden
Subject: Re: BLE RSSI questions

Hi Jeff,

my experience is same as yours, the RSSI is very volatile. I think you should not build on this value at all. The magnitude of it is what may be considered but not the actual value. It depends on a huge variety of factors. If you need to measure your antenna, then you'll have to buy a dedicated device. I'm pretty sure that the i* devices were not developed for precise measurement but for everyday operation.

Regards,

Andras

2013/2/25 Jeff Hosack <email@hidden>

1 - How accurate are the RSSI measurements intended to be? I was measuring the power of a device with my iPod in the open air; they were about 8 feet apart. I called scanForPeripheralWithServices and let it run for about 18 seconds, collecting didDiscoverPeripheral messages. The RSSI values ranged from -87 to -74 dBm over that time, a 13 dB range. Isn’t that range a bit wide?

2 - Are the RSSI measurements are averaged over time, or instantaneous? This is especially important to know for the readRSSI and peripheralDidUpdateRSSI combination. I intend to put the device and iPod in an RF isolated box and make measurements using these calls. I am hoping for a much tighter variance than 13 dB, so that I can determine if the antenna on my device is functioning as designed. I would like to make just one measurement, and get the correct value at that instant.

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References:
	>BLE issue with iOS 6.1 (From: Jeff Hosack <email@hidden>)
	>BLE RSSI questions (From: Jeff Hosack <email@hidden>)
	>Re: BLE RSSI questions (From: András Kövi <email@hidden>)