FlightAware Discussions

Positions Reported

Hi to all
In the Positions Reported box, I know what ABS-B and MLAT is.
But what is Other and how can I improve my score?

Well, better receiver, better antenna, better antenna position, amplifier, filter, different gain setting, shorter antenna cable, not necessarily in this order. It really depends where you start from.

In Australia we mainly have mode-S and ADS-B. The exceptions are old and very infrequent and can be ignored.

Simplistically, everything transmits mode-S. ADS-B equipped aircraft also transmit GPS location information.

The first packet received by piaware may or may not have GPS location.

If it does have GPS location it is classified as ADS-B position and if not it is classified as mode-S.

If enough other receivers that hear the mode-S packet are synchronized with your receiver then Flightaware may be able to calculate a location and send it back to you as an MLAT position.

If there are not enough synchronized MLAT receivers that have all received the data needed for FA to calculate the MLAT position it remains classified as a mode-S and no position information is provided.

All airlines and a large proportion of GA in Australia have ADS-B. If I sort the data table in Skyview by inverse source I get mode-S and MLAT at the top. When ADS-B aircraft come into range about 50% pop up as mode-S without position before changing to ADS-B within a few seconds when a location packet is received.

The same happens with MLAT. First sighting is mode-S and then switch to MLAT as FA calculate position and send it back.

I sync with about 50 other MLAT receivers many of whom have similar coverage to mine and so most mode-S only aircraft are eventually located by MLAT.

It seems that improving your receiver by having a better antenna and optimized gain and filtering for your location will increase your ADS-B and MLAT counts and decrease your mode-S only counts which are shown as Other. Other are actually aircraft for which there is no position information.

I emphasise that this is simplistically how it works in Australia where there is no TIS-B or UAT.

YMMV.

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Good point, Other are also Mode S messages, to quote the newsletter:

Other Mode S
The primary reason why a message would be classified this way in Skyview or on the My ADS-B statistics page is because the message was not an ADS-B position message and it was not received by enough sites at the exact same time to be used for MLAT purposes. It is normal to see a portion of your site’s messages fall into this category.

I think it is called Mode S Extended Squitter, which allows to send more information like gps position.

Thanks to all for the replies.

I live in the UK

I already have a Raspberry with.

Uputronics 1090MHz ADS-B Filtered Preamp

FlightAware Pro Stick Plus

Coaxial Collinear Antenna (home made)

FlightAware ADS-B 1090MHz Band-Pass SMA Filter, when added into the system it reduces the number of planes tracked.

FlightAware Pro Stick Plus is directly connected to the Pi.

In my FlightAware group I track the most number of aircraft, but my score is let down by Mlat and other results.

So I’m a little bit disappointed to say the least!

I will have another go at optimizing the gain.

That is two amplifiers. Try a gain of 30 as a start. You will probably need to go lower.

Apart from that make yourself a Spider antenna for comparison to check if your colinear is any good.

Where is your antenna mounted?
This is also always interesting to know:
(What is the Maximum Range I can Get?)

As a very rough guide to set gain:

Displaying the RSSI in SkyView:

Click on expand sidebar:
Screenshot%20from%202018-12-16%2010-44-54

Click the column head of RSSI twice so the numbers closer to zero are first:
Screenshot%20from%202018-12-16%2010-46-24

If there are many entries larger than -3, for example -2 you can reduce the gain.

If that RSSI of -2 or -2.5 happens very rarely you are just fine in regards to the gain.

If all entries are smaller than -4 then you may want to increase the gain.

If you have aircraft that vanish as they fly close by at low altitude that normally means the gain is too high to receive those. But if you don’t care about that you can optimize for plane further away. But that does not necessarily help to increase reception far away.

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If I run my setup with the highest possible gain, I see planes further away, but the message count goes down quite a bit, presumably because signals close by are too strong.

The number of aircraft stays roughly the same, the way the traffic patterns are sooner or later a message comes through and that is enough to count as an a/c.

Mlat messages count depends on the number synchronised feeders. To few, and there are not enough that receive the same message to calculate the position, to many and the chances that the data from your receiver is used for the calculation goes down and you’ll have fewer mlat position messages (but probabably more other messages).

My antenna is on the chimney about 30feet from the ground, in total about 180 feet above sea level, and the gain is set at 25.4

And my range is 200nm or so.

This site i presume?
(https://flightaware.com/adsb/stats/user/Gerry55#stats-68139)

Have you checked the displayed RSSI? Maybe a screenshot for the curious? :slight_smile:

Anyway your reception seems excellent.
Probably you receive pretty much everything there is to receive at your location.

Just more planes in other locations :wink:
Global ranking is not too useful on flightaware.
And you local ranking you get the best numbers.

Country of registration: Norway
Altitude: 10965 m | 35975 ft Squawk: 7552
Speed: 872 km/h | 471 kt RSSI: -27.0 dBFS
Track: 301° (Northwest) Last seen: now
Position: 52.877°, -5.198°
Distance from Site: 266.6 km | 144.0 NM

Feeder Type: PiAware (Debian Package Add-on) 3.6.3
Multilateration (MLAT): Supported / Enabled (synchronized with 164 nearby receivers)

That’s not what i asked. See my post a bit up.
Sort RSSI so the -2 -3 -4 -5 and so on is on the top.

A screenshot like this:

The problem is I’m unable to use Skyview with this feed, though I can with my third feed

I see. dump1090-mut has a similar table.
Is the feed not provided data by dump1090?

It has but this all I can access
ICAO Flight Squawk Altitude Speed Distance Track Msgs Ag

Well there is still trial and error.
You could reduce gain one notch and check if the <40 nm positions become more.
If the positions close in increase it could mean your gain was a little high. (But if it reduces positions really far out than you need to choose what you want or get a dongle with large dynamic range, for example the airspy mini)
Screenshot%20from%202019-01-03%2017-54-30

Also you already posted the RSSI of one plane
Speed: 872 km/h | 471 kt RSSI: -27.0 dBFS

I guess you can check in whatever interface you got that from.
Can you sort that interface?

No that’s from a spare Pi I have and the aerial is in the loft, and its connected to a cheep dongle and the reception is poor!

Why don’t you get more info from that other installation?
Or rather how do you get the information you get? :slight_smile:

I mean if you can change the gain then you can ssh/putty into the box right?

Then you could take a look at some of the json files.
For example for setting gain this would be most useful:
Run the following command:

cat /run/dump1090-fa/stats.json | grep total

And post the output here :slight_smile:

Sorry but I get No such file or directory with that.

Thanks to every one for the help, I think I will give up on this.

Which dump1090 version are you running?
The folder is different for the different versions.

Also i’m curious why you can’t connect to the webpage while you can access via ssh but if you don’t want to change that that’s fine :wink:
After all SkyView is really nice to look at.

You can try the following:

cat /run/dump1090-mutability/stats.json | grep total
cat /run/dump1090/stats.json | grep total