FlightAware Discussions

Signal difference is 8 dBFS. How much is this?

I receive a beacon signal from the same location with different antennas.
Simple complete antenna and directional antenna designed for 1090MHz

Simple antenna

Directional antenna
IMG_20200830_131213
The difference in the received signal is 8 dBFS. How to interpret this?

Wed Feb 3 17:31:54 2021 MSK dump1090-mutability v1.15-dev-334-g0ec2dd8 starting up.

Using sample converter: UC8, integer/table path

Found 1 device(s):

0: Realtek, RTL2838UHIDIR, SN: 00000002 (currently selected)

Found Rafael Micro R820T tuner

Max available gain is: 49.60 dB

Setting gain to: 49.60 dB

Gain reported by device: 49.60 dB

Simple antenna:

*91202002b82100003318f6d45ff5;
CRC: 000000
RSSI: -17.4 dBFS
Score: 1400
Time: 15825143.50us
DF:18 AA:202002 CF:1 ME:B82100003318F6
Extended Squitter (Non-Transponder) Test message (23/0)
Other Address: 202002 (ADS-B, other addressing scheme)

*91202002b8110000331af6c1f344;
CRC: 000000
RSSI: -18.7 dBFS
Score: 1400
Time: 25321720.92us
DF:18 AA:202002 CF:1 ME:B8110000331AF6
Extended Squitter (Non-Transponder) Test message (23/0)
Other Address: 202002 (ADS-B, other addressing scheme)

Directional antenna

*91202002b8210000338af6d18cd1;
CRC: 000000
RSSI: -10.1 dBFS
Score: 1400
Time: 421800624.67us
DF:18 AA:202002 CF:1 ME:B8210000338AF6
Extended Squitter (Non-Transponder) Test message (23/0)
Other Address: 202002 (ADS-B, other addressing scheme)

*91202002b8110000338af6d83b60;
CRC: 000000
RSSI: -12.2 dBFS
Score: 1400
Time: 423288718.08us
DF:18 AA:202002 CF:1 ME:B8110000338AF6
Extended Squitter (Non-Transponder) Test message (23/0)
Other Address: 202002 (ADS-B, other addressing scheme)

*91202002b8110000338bf6d636e0;
CRC: 000000
RSSI: -12.3 dBFS
Score: 1400
Time: 427296969.67us
DF:18 AA:202002 CF:1 ME:B8110000338BF6
Extended Squitter (Non-Transponder) Test message (23/0)
Other Address: 202002 (ADS-B, other addressing scheme)

*91202002b821000033d2f63db0c3;
CRC: 000000
RSSI: -12.5 dBFS
Score: 1400
Time: 709850715.67us
DF:18 AA:202002 CF:1 ME:B821000033D2F6
Extended Squitter (Non-Transponder) Test message (23/0)
Other Address: 202002 (ADS-B, other addressing scheme)

*91202002b811000033d2f6340772;
CRC: 000000
RSSI: -11.9 dBFS
Score: 1400
Time: 711338809.17us
DF:18 AA:202002 CF:1 ME:B811000033D2F6
Extended Squitter (Non-Transponder) Test message (23/0)
Other Address: 202002 (ADS-B, other addressing scheme)

Every -3 dB reduces to half
Every +3 dB doubles

+9 dB = 2 x 2 x 2 = 8 times
-9 dB = ½ x ½ x ½ = ⅛ times

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Great coincidence. Today couple of hours ago I posted this:

https://discussions.flightaware.com/t/directional-antennas/19586/53

 

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10(8/10) = 6.3x difference in power.

(or, equivalently, 10(8/20) = 2.5x difference in voltage)

2 Likes