What in the purple hell was that???

[Ray Tackett]

Ray -- ADS-B operates at 978 and 1090 MHz. The echoes that are discussed are from primary radar, not DME/Mode C transponders, as I understand it.

Yep, and radar used to operate in what is now the FM broadcast band. Shorter wavelengths equal more fun with reflections, absorbtion, and interference patterns, regardless of the information which modulates the carriers.

Back in the mode C days, when I was flying traffic watch on weekday evenings, I almost got in Class B trouble due to a flaky transponder. It had me at illegal altitudes, and very erratic speed indications (evidently variations in return latency). Eventually PNE Tower got hold of me on the radio, and asked me to make a pass over the airport at a particular altitude and airspeed. Their radar display was showing crazy stuff coming from my transponder, but looking out the window, it was obvious I was doing what I had been told.

That, and the fact that I interacted professionally with towers at PHL, PNE and sometimes TTN several times every day gave me a far better reputation than any piece of hardware from Happy Herbie's Used Airplane Lot. (That's what I called the excessively low-budget flight school/rental/charter biz I flew for.)

[Russell Holton]

Shorter wavelengths equal more fun with reflections, absorbtion, and interference patterns, regardless of the information which modulates the carriers.

As I understand it, ADS-B is usually triggered by a radar sweep. In a congested airspace with multiple radars, two transponders could be triggered at the same time. The parity bits may not catch the corruption every time.

What we're seeing is a "still". I'd like to see what the "movie" it comes from reveals.

[Scott Dyer HPN/NY]

As I understand it, ADS-B is usually triggered by a radar sweep. In a congested airspace with multiple radars, two transponders could be triggered at the same time. The parity bits may not catch the corruption every time.

What we're seeing is a "still". I'd like to see what the "movie" it comes from reveals.

No, Russell, ADS-B out transmits every second, regardless of radar coverage.

[Scott Dyer HPN/NY]

Yep, and radar used to operate in what is now the FM broadcast band. Shorter wavelengths equal more fun with reflections, absorbtion, and interference patterns, regardless of the information which modulates the carriers.

Today's primary radar is S band, 2.42.7 GHz. Nothing like 978 or 1090 MHz.

[Russell Holton]

No, Russell, ADS-B out transmits every second, regardless of radar coverage.

Either way, in a congested airspace, packets will get stepped on.

[Terry Carraway]

But missing packets will not make MACH 4+ speeds show up.

[Scott Dyer HPN/NY]

But missing packets will not make MACH 4+ speeds show up.

And, if erroneous data is shown on a 1 second burst of received data subject to interference, it will be corrected in the next second. There are a lot more ADS-B receivers out there than radar sensors, too, so interference at the source isn't the same problem.

[Stephanie Belser]

Anyway, I'm thinking of getting or building an ADS-B receiver and plugging it into that website to improve coverage. I'll have to see if I can do it for under 0.1 AMUs

[Scott Dyer HPN/NY]

This will get you started on hardware, Steph. https://flightaware.com/adsb/piaware/build

[Stephanie Belser]

This will get you started on hardware, Steph. https://flightaware.com/adsb/piaware/build

Thanks. If I do it, I'll feed it to ADS-B Exchange, as they claim that they don't filter the results.

[John O'Shaughnessy [FCM]]

This will get you started on hardware, Steph. https://flightaware.com/adsb/piaware/build

I've got one of these feeding up into Flightaware.

[Scott Dyer HPN/NY]

Thanks. If I do it, I'll feed it to ADS-B Exchange, as they claim that they don't filter the results.

Yeah, I know, but aside from the software it gives you an idea of hardware requirements.

[Tom Tyson]

Are those the ones we built in DLH at the GIG a few years ago?

[Scott Dyer HPN/NY]

Those were ADS-B In receivers, not the Out receivers. Got wx, traffic, etc. Even from the back seat of the KingAir....

[John O'Shaughnessy [FCM]]

Are those the ones we built in DLH at the GIG a few years ago?

Not exactly, but they are 90% the same under the hood. Both are based on a Raspberry Pi, and both use software-defined radios to tune in the appropriate frequencies. Both also use about 80% of the same software too.