I just bought a pro stick plus and was thinking about adding my nevis adsb filtered preamp to it. I used the nevis when I was using my mode s beast until the sma connector broke. Is there any upside or downside to adding the nevis to the pro stick plus?
Sure you can use it you have an overcrowded frequency environment. I mean a lot of near gsm base stations and so on.
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Thanks…
How would you define a lot of gsm base stations?
I am curious to see at what point this could be impacting performance. I have line of sight of less than 1000meter or yards to six all operating in the 850/900Mhz bands.
A lot of people have made such experiments and studies. Just put a filter and you will notice the improvement. And it is not only in plane count, but also range.
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The only problem I can think of is receiver stick saturation if you use a preamp (nevis) in front of a preamp (pro stick).
I have the FA antenna → 5 meter of LMR400 → FA filter → Pro stick and the stick seems to be overloaded when aircraft are in close vicinity (already lowered the gain).
I’m currently trying different things to overcome this …
To capture both nearby and distant traffic at some sites we’ll run two receivers, one with an amp and one without (or even one with an attenuator for very close traffic on the surface).
This is exactly what I used to do sometimes ago:
One system with high gain FA Antenna+Filter+ProStick (which has integral amplifier)+Reduced Gain Setting (due to cell phone antennas nearby)
Other system with low gain Cantenna+Generic DVB-T (Black)+Gain max
Don’t wanna hijack this thread, but may i ask a short question: I was also thinking of using a second receiver set. I have a noelec-smart stick left. Can i use the same Rpi3 for the second stick and merge the streams maybe using a maxrange setting of 10 NM for the second stick to avoid a lot of duplicate messages (second instance of dump and/or modesmixer)?
If a solution was already posted, a link would be enough.
Another question: Is there a logfile for dump1090-fa like the one for dump1090-mutuability in /var/log - cannot find an appropriate logfile for the FA version?
Merging data from two receivers will break mlat if you feed the combined data to piaware
Dump1090-fa logs to syslog, but it is pretty quiet so you won’t see much
Thanks for the hints, I found older threads about combining two or more receivers, I dug through them and started to reorganize my setup.
What exactly will break this? The duplicate Mode S or ADS-B reports or both?
Having two different sets of timestamps from different clocks is what breaks it. The mlat server needs to maintain a clock model for each receiver and the Beast protocol has no way to say that data is coming from different receivers, so the server will try to synchronize both receivers as if they were a single receiver with identical clocks and sample counts which just doesn’t work.
I assume that ADS-B reports of several different feeders are interpolated to get to know their time difference and this information is used in the calculation of MLAT solutions out of Mode S reports.
So to filter out Mode S reports from the secondary receiver will not help? As I don’t wanna break things and I will create a merged feed just for internal usage.
Essentially yes. ADS-B position reports are used as a kind of common beacon to work out the clock offset and frequency difference between pairs of receiver clocks (nb: a clock driven by counting received samples, not the system clock) and then that information is used to convert the arrival timestamps of Mode S messages on different receivers to a common timescale so the difference in the arrival time can be calculated.
So to filter out Mode S reports from the secondary receiver will not help? As I don’t wanna break things and I will create a merged feed just for internal usage.
You could zero out the timestamps of messages from the secondary receiver entirely and they would be ignored by the mlat client.
But the better approach, if you can, is to run two piawares, one per receiver, taking the raw feeds, and merge the data for your own use separately.
Ok, understood. Thank you obj