StratuX ADSB Traffic

[John W 4sba]

I'm posting this in the hope that it can start yet another conversation
on this popular topic that can be helpful for Avare users searching the
Forum for info or solutions.

Traffic may sometimes seem spotty with StratuX on Avare. I recently
passed less than two miles from a faster converging aircraft at my
altitude that did not show in Avare using StratuX. Due to a smoky day
from distant wildfires and the sun being somewhat near the target
location, I couldn't see it even after making a Flight Following
recommended turn. It was finally obvious less than a minute later very
near where I'd have been on my original heading.

My observations:
*The range setting is a factor in some cases. To reduce clutter Avare's
"Filter ADSB Traffic" setting (8th item at
Map->Menu->Preferences->Display) has a maximum of 100,000 feet (about
16nm). So traffic seen by StratuX or other sources won't be shown
beyond that or whatever range "Filter" setting is selected.

*StratuX is a relatively inexpensive receiver that may not compare
favorably with commercial units using more expensive components. Also,
the firmware (software) in StratuX units may be less robust and
sophisticated. All receivers are also sometimes offered firmware
updates that can improve performance and reliability.

*There seems to be some kind of "reliability" feature in how apps
display traffic data. I notice that different apps display some traffic
not shown simultaneously with other apps using the same source.

*Some traffic is using ADSB's 1090 frequency broadcast direct from the
aircraft, and others use the 978 frequency. The latter is broadcast by
FAA ground transmitters which may not be received at some locations
(e.g. remote or mountainous areas). In such locations even airliners
broadcasting 1090 from 33k' altitude need to be relatively close to be
within maximum Filter range. Placement of transmit and receiver
antennae on/in the aircraft is also a significant factor and the signal
is inevitably degraded by the airframe(s).

*With several steps in the process there is some delay between the time
a target's location is determined by ADSB, and it's displayed on any
app. I've often spotted fast movers far ahead of where ADSB shows them.

*To my knowledge FAA radar data is still not included in their ground
station traffic ADSB data transmission. So ATC may see nearby traffic
that won't be displayed.

My Policy: Assume that relevant traffic may not be displayed correctly
if at all, and that ADSB Traffic is at best an excellent extra set of
"eyes" in the cockpit. Flight Following adds the FAA's radar "eyes" but
keep in mind that the controller may be busy or distracted.

Do you have comments or additional info to share on this topic?

Comment: It's likely the traffic I encountered had an opposite-wingtip
mounted 1090 ADSB transmitter or (being non-ATC contact VFR outside a
mandate area) none at all, but was detected by a nearby FAA radar. I'm
lucky to have been flying in the U.S. with Flight Following and an alert
controller.

[Eric Jacobsen]

I'm an EE that has spent several decades working on various wireless systems, including several projects using the same platform that the Stratux uses, specifically RTL-SDR receiver dongles and a Raspberry pi (or other comptaible Linux-ARM platform).    The receiver dongles and the software are not the performance limiters for the Stratux, they're actually quite good.   Usually ADS-B-in performance degradation comes from antennas or placement or unavoidable shadowing at either the receiver or the transmitter.   No wireless link is 100% reliable, and without multiple external antennas per band the likelihood of shadowing from wings or other aircraft structure is always an issue.    On the transmitting aircraft the same shadowing issues happen even between the external transponder antenna and the direct path to your receiver.   Terrain or other obstructions can get in the way as well.   UAT retransmits may help you still see an otherwise shadowed airplane on your display, but you get the idea.

I have a dual-band Stratux that spends most of its time hanging in one of the rear windows in my airplane (a Mooney).  It feeds the two tablets I fly with that run Avare.  I also have an in-panel UAT ADS-B-in receiver that feeds my in-panel IFD540 navigation display.   The in-panel ADS-B-in UAT receiver is fed by an external antenna on the belly of the airplane.   I've flown with this configuration for several years, probably five or six hundred hours.  It is not unsual for traffic to appear on my EFBs from the Stratux that does not appear on my IFD, and vice versa.   The in-panel receiver and display are all certified devices.   It's not a receiver or software quality issue on either device, it's just the nature of wireless signals.

Basically I agree with your conclusions that it is still a Good Idea to look outside for traffic.    I'm glad your situation came out well.   I'm really just addressing your comments that the quality of the Stratux was a factor, which I can say it is not any worse than anything else, and better than some others.   The same issues that affect traffic reception in a Stratux will affect any other ADS-B-in receiver.  The best way to improve that performance would be to mount multiple external antennas, per band, carefully mounted to provide more consistent directional coverage, and make a diversity reception system.   That would improve reliability, but it's a lot of effort and the difference may not be huge, and it still won't overcome shadowing from the transmitting aircraft, tower, or terrain.

[mcso...@gmail.com]

I didn't see whether you have 'out' installed. If you don't have 'out', and/or the other guy didn't have 'out', then the ground transmitter wouldn't send a reply to the Stratux.

Having said that, in my limited flying with a uAvionix in/out, I've seen the same target go on/off repeatedly over several minutes. ADSB is far from a perfect system and our hardware is only a small part of the equation.

[johngo...@gmail.com]

I too use a stratux for gps, uat, and 1090.

Today during a flight I saw very close traffic at my altitude about a mile ahead and on the 180 course, closing fast, we both turned to our rights, no problem.  

However, I wondered why I did not see him before on the avare display, so I looked and there he was behind me now.  Why did I not see him earlier on the avare display?  Because the background map image so cluttered the display as to mask the target approaching.

I know there is a way to filter out adsb traffic beyond so many feet, so why not have a feature whereby if a target is within say 3000 ft the map is replaced with a blank screen every other second for 0.750 seconds, that would still show the traffic target in the correct relative position with zero display clutter.

The flashing background map would serve as an attention getter.  While the map is blanked out the relative position of the target is unmistakable.

I would like that.

jg