The goal has never been to reduce the strong signal rate. The goal is to improve overall reception, and the strong-signal rate is one metric you can use to tune that; it’s an indication that you might be losing some signals at the strong end of the range which you might want to receive.
What other metric are you suggesting?
(One thing I’ve been considering is to look for full-scale values in the IQ samples, as an alternative indication that the ADC is hitting the top of its range. However, there’s a lot of digital baseband processing that goes on in the RTL2832 between the raw ADC values and the sample values we get, so I’m not sure how useful it’ll be)
Well the usual guidelines don’t tell you to reduce the percentage to zero.
I think most people do understand tweaking for that percentage is just to get you in the ballpark.
It usually works just fine to set it to 1% to 5% and it’s in most cases pretty optimal.
If you’re interested mostly in nearby aircraft, then reducing the percentage to something really low makes perfect sense.
Anyhow it’s always a compromise and rough guidelines is what most people are looking for.
Everyone is welcome to use their own judgement.
If you have a few signals that get to the 100% of the digital range it’s fine. But once you have multiple strong signals, they start to overlap statistically. Signals are not correlated, so the more planes you can see, the more probability of collisions increases.
There is no mechanism for solving collisions.
So the overlapped full scale signals will start merge one with the other, loosing the transitions (fronts). Impossible to recover the data.
On the other hand, if you have some delta between levels, the software can still detect the transition.
Overlapping messages are unlikely to be decoded by rtl-sdr anyhow.
And that’s not the issue with having the gain too high.
I don’t have enough background to know what the exact cause is, but from my understanding part of the analogue portion gets overloaded and the signal gets distorted from the overload.
There aren’t enough collisions that would explain completely loosing reception on a close by helicopter / aircraft when you have the gain set too high.
I have a very dim decades old memory of a capacitor with a time constant that was slightly too long such that weak signals in a timeslot directly after strong signal were lost. It was in a military packet radio but I can’t remember the exact circumstance. I do remember that it drove us nuts trying to track it down.
I thought about this many times in the past years, never had time or energy to dig into the code to see how it’s currently being handled, but have always figured that packing unprocessed (otherwise discarded) stream into arrays sorted by signal strength for post-processing could help. That said, I’m smart enough to realize what I don’t know, and no clue of the feasibility of such processes or if even possible to reliably sort bits of the stream by signal strength to begin with - although I’m pretty sure this already being done in some capacity.
The premise would be to follow the logic that bits/chunks of the same strength would more than likely belong to the same transmitter (within a logical timeframe) and these fragmented packets could be chained together to see if they pass a round of error checking before being flushed. I’m talking a bit out of my arse since I haven’t written a line of code in a couple years now outside of some basic patches or otherwise kindergarten level work…
That’s true for amplitude modulated signals.
But here we have digital signals, more like FM. A clipped signal versus a clean sinus wave is preferable. I think that the front of the signal (or transitions) are used to demodulate the signals. What the tip part looks like is probably not that important as long as is fairly flat.
But I admit I can be wrong. Sometimes an overload amp will “clamp” up and stay like that for a while. Don’t know if the CMOS parts inside decoder chip do that.
