-49.5 dBFS is a raw signal level of zero, so yeah, you will see this for aircraft where you are receiving only synthetic messages (anonymized mlat, mlat during the period after the aircraft has left your reception range but before the mlat server stops feeding you results)

The particular plane involved passed almost directly over my location, and I received messages from about 200 nm away both coming and going. It displayed -49.5 the entire time.

When you say “anonymized mlat”, are you referring to aircraft that have been obfuscated to keep the information from the public?

See the mlat announcement post for details.

Hi, I have tried to reverse engineer your set-up, is this correct?

Would be very cool to see a bill-of-materials for this… :slight_smile:

simpler and better … The Final Filter Shootout

I have filters like that. I bought 6 1090Mhz and 6 978Mhz for about $30 each.
The dongle is a std rtl-sdr($US20) and the amp is maybe another $20.

It looks well engineered. I probably would have put the amp inside a metal, to reduce noise, especially from the AC/DC converter.

About RSSI: i use a RTL-SDR dongle in my setup. I can see anywhere from -1 to -34 reporting ADSB messages with correct position. Of course, -34 from planes far away, around 70nm and my antenna is just a half wave dipole on my desk, which is respectable.
On the other hand, I tried a FlightAware blue dongle from a friend, and indeed can’t see anything below -20, and even then the position is not decoded.

I am using the blue FA stick on both of my receivers and have no problem receiving signals with an RSSI below -20

Looking at my map now with low traffic i have at least three aircraft with an RSSI below -25 and all are visible on the map

Probably didn’t reduce the gain.
Might also be interference there giving the ProStick trouble.

Maybe do a scan: Do I Need A Filter?

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Consider the poor location of your antenna. You are probably loosing signal due to terrain (hills, trees, buildings) rather than receiver sensitivity.
You’ll probably see a massive improvement if you can get you antenna a lot higher.
Of course, a decent antenna would help a lot too.

FA blue dongle
Jetvision antenna on the roof
NO filter

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No, this is not the problem. I explained in another topic that replacing the blue dongle with RTL-SDRv3 gives me way better results using same antenna (there is no cable, home made antenna connected directly).

Better results in what? A comparison of all values which are better would be good.
AFAIK the RTL-SDR does not perform as good as long as no LNA and Filter is used

RSSI goes down to around -33 on RTL-SDR. Does not have a filter in front and only a dipole.
That difference in RSSI is reflected also on distance, which goes even above 100nm with RTL-SDR.
Tried to troubleshoot why the FA blue dongle does not perform as it should but no good answer yet.

Only thing left, interference:
Do I Need A Filter?

Do a scan with both configurations i possible.

Last possibility: the blue SDR is just defective.

Did that. There is 3 and 4G nearby in 800 and 900Mhz band but seems not to be a problem since RTL-SDRv3 in handling them just fine with just a dipole.
Trying to construct a new CoCo antenna which has narrower bandwitdth but for the moment I am fighting for time to do so.

You might just not believe me, but there are have been quite a few reports of unamplified SDRs working better for them due to interference.

The LNA itself (not the receiver behind the LNA) is somewhat susceptible to interference.
I’m not sure which band is the issue, it might well be FM or even AM that overloads the LNA in the blue stick.
As it has no filter before the LNA, the fix is to add one of the FA barrel filters in front of the ProStick+.

Which particular problem?

Antenna at ground level?
local obstructions?
They will all degrade your sites performance

So does the blue FA, at least the two ones i am using.
I think if it’s not performing pretty well for you, it might be your environment. Or as @wiedehopf said a broken stick

Merry Christmas and happy holidays, all -

I’ve finally moved into the house which I bought back in January this year and set up my PiAware site 5163. I had hastily set it up with the FA gain omni up on the roof, and given all the other things I had to deal with (remodel, day job, Covid pan., I never spent any time investigating why, with me line of sight and looking downhill into KPHX, I’d rarely hear planes landing or on the ground.

So on this wonderful Friday, after now living in the house since the first of this month, I decided to figure out what was up. OBJ’s and Nitr0’s wisdom documented here live on for the ages, and in a few minutes I rediscovered the darned gain adjustment command.

I checked my Pi, it was running “max” gain, so I turned it down to 45, then gradually brought it down to 25 where almost none of my traffic is peaking above -3 RSSI. Suddenly, I got coverage - Yeay! Merry Xmas to me!

Currently this station’s at a ranking of 1361 - I’ll circle back in a few days and see how it’s doing!

Cheers - Jon N7UV

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