MLAT results degrading?

[moscho]

Hi everyone,
Just joined today to this forum, but a frequent reader in the past myself. Happy to be here at last!

First some background:
My station (EXTRPI590582) is a year old now and consists of a RPi 3B+ running bullseye. I'm using the recommended software for AirnavRadarBox, with the green ADS-B flightstick connected to an AirNav Radar ADS-B XBoost antenna. Data is fed thru RJ45 to my router. Not using other tracking software and not sharing data with other flight trackers.
Last year I've tested different positions for my ADS-B antenna, and lately (around January) I decided to move it to a mast I have attached to my roof's chimney, where I had rigged my old discone. I, of course, updated my station's height variation, +/-3 meters higher now.
I live in a 1000m AMSL town near Madrid, and my roof is *almost* free of obstacles. This last year the data results have been good, but with the new antenna position I got a max coverage of around 590kms and ranking position of 30-40th (for Spain), really better. I have MLAT active from the start and the usual number of synced stations was close to 30. Messages received were more than 1million/day, with position data around 75%.
Now, some days ago I noticed a sudden drop in ranking position down to 58, today 59th. Also, the MLAT synced stations dropped to just 4! Strangely, the number of messages is consistent if I have to give credit to my station's status panel.
My question is: Maybe something (like the last weeks constant rains) degraded my coverage? Or, is it a problem with the servers statistics not reflecting my real results? I read some old posts talking about these issues. Checked my antenna/cable/connectors as well and all seems ok. But, overall, MLAT results baffle me. Of course, I rebooted my RPi some times after apt upgrades with no apparent errors, and also checked that data is flowing as usual, netstat shows the connections working, rbfeeder systemctl status is ok, etc. By the way, I suppose myself competent enough at CLI.

Any suggestions are welcome!
Cheers

[Runway 31]

Just had a look at your station coverage map (shot attached) and note that while you have good coverage to the south  and south east it is quite restricted in the other directions, especially to the weast.  Was it like this before you moved the antenna.  There appears to be something blocking your coverage in all directions apart form the south, south east and north east which might need looking at as everything else appears to be ok

Alan

[moscho]

Hi Alan,

Yes, those restrictions are assumed since I started my station. There is a mountain range back to my NW which is around 1700 mts. high, and some roofs around that shadow my coverage. These limitations have been the same all the time.

As I said, I guess I gained some more coverage with said antenna moving up, considering the increase in range that lasted for a while. Just for the record, I remember reaching both north and south spanish shores easily and radius getting to Mallorca at the east, also had four or five MLAT stations synced in Portugal to my west, apart from all the others totaling around 30 stations. Now they are just 4!

The problem is that those gains have been reduced drastically on the last weeks without me changing any configuration. Mostly the number of MLAT stations synced. And that was what I was asking about. I'll wait some days to see if it goes back to the great results I had. Maybe it's just too cloudy and rainy lately and this limits propagation...

Anyway, thank you very much for the quick response.

[Runway 31]

Cloud and rain will decrease performance

I used to have 55 or so stations synced but now showing 30.  Only stations within 4 or 5 miles are required for MLAT calculations to its possible they have rejigged the algorithm to cut out ones far away that are of no use for calculations

Alan

[moscho]

Hi Runway 31,

I didn't realize that fact: MLAT far stations not very useful for calculations, neither 'they' could change the algorithms without warning. Maybe it's all related to that, hopefully.

And as ranking positions tend to change a lot I won't do much fuss about it. Guess the number of messages with position is a better measure of radio performance.

Happy to be contributing anyway.

Thanks for your answer!

[moscho]

Well, today I've noticed the MLAT synced stations row has adjusted itself back to 27. Don't really understand this, maybe I shouldn't obsess that much...

[edit]
Oh, OK. I've read some other posts now related to MLAT, and it seems they managed to fix the issue.