RTL-SDR v4 with the dipole antenna it comes with (set up with 6cm length on each end) mounted inside my house by a window (I have plans to set up a proper antenna outside in a couple months)
Uputronics filtered LNA powered by Bias-Tee
Raspberry Pi4
Software:
readsb, tar1090, graph1090
My Messages > -3dBFS averages to 0.4%
I live within 50 miles of a major airport, and aircraft frequently pass within <1 mile horizontal distance from my antenna on their approach to said airport. I’m using readsb’s autogain, but it almost always keeps the gain at 48-50. I’ve read that I should have the gain set to ~35 with an LNA, but manually setting the gain to various values seems to have a negative impact on performance over just using autogain.
What gain settings should I be using? How do I properly determine this? The methods I’ve found online appear to have been replaced with automatic methods such as with readsb.
Does graphs indicate “ideal” conditions, and if not, how do I improve it?
Any other insights from reading the graphs? I’m not sure how to determine issues from any of these graphs, besides the gain problem mentioned above.
The main thing that will be a “problem” for you is that you have a fair number of airplanes somewhat close to you and if the gain is turned up too much those signals will be too strong and overtalk weaker signals. Since your number of very strong signals are low enough, it seems the auto gain is doing its job correctly. I was going to post about using the gain optimization scripts but it is not recommend to be used anymore with current setups. Script can be found here → Automatic gain optimization for readsb and dump1090 fa
The chart with ADS-B track seen can be your best clue about how well the site is setup. In a perfect world there should be nearly zero tracks with a single message. Those normally happen from decoding errors which could be caused by a lot of things but mostly bad gain settings. To my eye, it seems good enough and not much of a concern.
Yeah, that script (and forks of it) were the main tool I was finding for optimizing gain. I guess it’s safe to assume then that letting readsb’s autogain keep my gain setting between 48 and 50 is okay, even when using an LNA?
Yes, because you are using a dipole which is 6cm + 6cm (1/4 wavelength + 1/4 wavelength). This dipole has a low gain of 2 dBi. This low gain, coupled with indoor location of your antenna, means even with LNA, you will need a high gain setting like 49 or 50.
When you will use a higher gain antenna ( say 6 dBi or 9 dBi ), mounted outdoor on roof, the autogain is likely to reduce gain setting.
