Firstly, there are so many gain posts, some of which are dated, I thought I would put this up for comments.
For the hell of it, I thought I would do a 12 hour gain test. Now this was between 6.00 am and 6.00 pm, , with a reasonably large regional airport near by and also a Defence Basic Flight School operating out of the same. My coverage footprint extends down towards Sydney and covers the north west and west approaches to Sydney from Asia and Europe. Average ADS B positions reported during bushiness days between 95,000 and 126,000 positions.
Using the popular original gain scripts, a Prostick Plus, a bias t power injector and a RTL-SDR Blog ADS-B Triple Filtered LNA (Bias Tee Powered, a DPD ADS-B Vertical Outdoor Base Antenna 9db gain), up the top of the pole, utilising Power over Ethernet and a POE Hat, a PI 3B+. 62 seconds over 66 runs,(each run took about 11 minutes to complete) utilising all possible gain settings, including AGC and -10.0 (reason for all possible gain settings, I have found some smaller gain tests resulting generally in the best setting being below 20.0, probably due to the setup,high gain LNA and a high gain antenna. I don’t need much gain to get high figures, SNR reasonably good as well.
The below results are reasonably self explanatory,EXCEPT for the Aircraft result: The results will have Gain, Messages, Positions, Aircraft and largest to smallest including the relevant gain numbers included:
Meassages:
GAIN - MESSAGE - POSITION - A/C
12.5 - 201422 - 45876 - 281
8.7 - 200743 - 45704 - 278
15.7 - 200408 - 45461 - 282
14.4 - 200179 - 45525 - 282
7.7 - 199577 - 45506 - 280
16.6 - 198277 - 44809 - 283
3.7 - 195659 - 44758 - 278
19.7 - 195542 - 44235 - 282
2.7 - 193715 - 44366 - 277
20.7 - 190725 - 43231 - 284
22.9 - 181904 - 41599 - 283
1.4 - 180832 - 41622 - 278
0.9 - 176269 - 40642 - 275
25.4 - 174166 - 40059 - 282
0.0 - 158133 - 36595 - 270
28.0 - 153583 - 35886 - 285
Positions:
GAIN - MESSAGE - POSITION - A/C
12.5 - 201422 - 45876 - 281
8.7 - 200743 - 45704 - 278
14.4 - 200179 - 45525 - 282
7.7 - 199577 - 45506 - 280
15.7 - 200408 - 45461 - 282
16.6 198277 44809 283
3.7 - 195659 - 44758 - 278
2.7 - 193715 - 44366 - 277
19.7 - 195542 - 44235 - 282
20.7 - 190725 - 43231 - 284
1.4 - 180832 - 41622 - 278
22.9 - 181904 - 41599 - 283
0.9 - 176269 - 40642 - 275
25.4 - 174166 - 40059 - 282
0.0 - 158133 - 36595 - 270
28.0 - 153583 - 35886 - 285
Aircraft:
GAIN - MESSAGE - POSITION - A/ C
28.0 - 153583 - 35886 - 285
20.7 - 190725 - 43231 - 284
16.6 - 198277 - 44809 - 283
22.9 - 143247 - 33577 - 283
29.7 - 181904 - 41599 - 283
14.4 - 200179 - 45525 - 282
15.7 - 200408 - 45461 - 282
19.7 - 195542 - 44235 - 282
25.4 - 174166 - 40059 - 282
38.6 - 92118 - 22129 - 282
12.5 - 201422 - 45876 - 281
Now you will note, Messages and Positions both have 12.5 as the winner. Aircraft though has 28.0, double the gain and some, of the other 2 gain fields. A quick observation from my end though, on smaller tests 62 secs and below and over only say 15 to 30 secs, the 3 data fields generally are the same gain level. Long and more extensive checks, generally have the messages and positions the same, but Aircraft different gain level.
Please feel free to comment and may be explain why the Aircraft gain level, over that length of time, would be so different to the message and position. What causes this?