# Difference of two RSSI value

**URL:** <https://bbs.aprbrother.com/t/difference-of-two-rssi-value/1602>\
**Category:** AprilBeacon\
**Created:** [May 21, 2020, 12:54pm UTC](https://bbs.aprbrother.com/t/difference-of-two-rssi-value/1602 "2020-05-21T12:54:45Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![pauldeng](https://bbs.aprbrother.com/user_avatar/bbs.aprbrother.com/pauldeng/32/440_2.png) [@pauldeng](https://bbs.aprbrother.com/u/pauldeng)\
**Post date:** [May 21, 2020, 12:54pm UTC](https://bbs.aprbrother.com/t/difference-of-two-rssi-value/1602/1 "2020-05-21T12:54:45Z")

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Hi,

I received a raw beacon message from gateway V4 v1.2.5.22 below:

`00 dd cd 99 db 44 48 d3 02 01 06 1a ff 4c 00 02 15 fd a5 06 93 a4 e2 4f b1 af cf c6 eb 07 64 78 25 00 01 00 02 d8`

- Based on the header [info page](https://wiki.aprbrother.com/en/User_Guide_For_AB_BLE_Gateway_V4.html#data-format), the byte 0xd3 is RSSI = 0xd3 -256 = -45.

- In the raw advertising data format below, the byte 0xd8 is RSSI at 1m = 0xd8 -256 = -40.  

Why there are two RSSI value, what is the difference?

Thanks.

Cheers,  
Paul

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**Author:** ![aprilpea](https://bbs.aprbrother.com/user_avatar/bbs.aprbrother.com/aprilpea/32/9_2.png) [@aprilpea](https://bbs.aprbrother.com/u/aprilpea)\
**Post date:** [May 22, 2020, 3:00am UTC](https://bbs.aprbrother.com/t/difference-of-two-rssi-value/1602/2 "2020-05-22T03:00:04Z")

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The 0xd8 is measured power bit. see [What is Measured Power](https://wiki.aprbrother.com/en/How_to_use_ApriliBeacon.html#what-is-measured-power)

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<div class="post-metadata">

**Author:** ![pauldeng](https://bbs.aprbrother.com/user_avatar/bbs.aprbrother.com/pauldeng/32/440_2.png) [@pauldeng](https://bbs.aprbrother.com/u/pauldeng)\
**Post date:** [May 22, 2020, 6:17am UTC](https://bbs.aprbrother.com/t/difference-of-two-rssi-value/1602/3 "2020-05-22T06:17:47Z")

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Thanks for you quick response, I still a bit confused.

Let me try to understand:  
 ![beacon_rssi](https://bbs.aprbrother.com/uploads/default/original/1X/4657755c32d16e60383052d280f362bdde34c3f8.png)

1. For example, gateway measures RSSI of the beacon message from a beacon device one meter away
2. This RSSI is the Measured Power
3. This Measured Power value then is hard coded into beacon message as a reference?

My question is what the beacon’s transmitting power is when measure this Measured Power?  
If I change the transmitting power on beacon device, does this reference will also change?  
Do you have a table mapping the Transmitting Power --\> Measured Power?

Thanks.  
Paul

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<div class="post-metadata">

**Author:** ![aprilpea](https://bbs.aprbrother.com/user_avatar/bbs.aprbrother.com/aprilpea/32/9_2.png) [@aprilpea](https://bbs.aprbrother.com/u/aprilpea)\
**Post date:** [May 22, 2020, 6:23am UTC](https://bbs.aprbrother.com/t/difference-of-two-rssi-value/1602/4 "2020-05-22T06:23:37Z")

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> [@pauldeng](#):
>
> If I change the transmitting power on beacon device, does this reference will also change?

No. You need do measure RSSI at 1 meter and write new measured power to the beacon.

> [@pauldeng](#):
>
> Do you have a table mapping the Transmitting Power → Measured Power?

No. It’s depend on your hardware. For Transmitting Power 0dBm, the measured power is usually -59dB.

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<div class="post-metadata">

**Author:** ![pauldeng](https://bbs.aprbrother.com/user_avatar/bbs.aprbrother.com/pauldeng/32/440_2.png) [@pauldeng](https://bbs.aprbrother.com/u/pauldeng)\
**Post date:** [May 22, 2020, 6:30am UTC](https://bbs.aprbrother.com/t/difference-of-two-rssi-value/1602/5 "2020-05-22T06:30:35Z")

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Hi,

Thanks for your support.

Now I understand. It is a value for me to set based on my settings and calibration.

This is very helpful, thanks.  
Paul