Navworx TransMonSPE USB cord & wifi interference

Somehow, the USB cable from our Navworx EXP box to the TransMonSPE squawk & altitude sniffer is messing up the wifi from the EXP box. I?m not sure what?s going on (or how to cure the problem).

With the USB cable connected, we have consistent trouble with the EXP wifi, both in staying connected to the EXP configuration app on the iPad and (less frequently) in maintaining a consistent ADS-B device connection on ForeFlight. Although the wifi is a problem, the rest of the system seems to work fine. We flew yesterday and got a clean report from the FAA?s ADS-B report site, and we saw WX and traffic on our MGL Odyssey G2 EFIS and most but not all of the time on ForeFlight.

What?s where:The EXP box is mounted on a plate attached to the side of the fuselage behind the rear baggage bulkhead. The UAT antenna is mounted back there, on the bottom of the airplane, and per instructions is more than 5? from the transponder antenna, which is connected to the transponder cable under the front right corner of the passenger seat pan, just aft of the wing spar. That?s where we?ve put the TMSPE, with its USB cable routed along the right side of the airplane back to the EXP box. The transponder is a Garmin 320a.

Today was the first time we did a bunch of tests all outside our hangar (as opposed to some engine-off tests we did in the hangar, when we were installing everything).

• With the USB cable connected from the EXP to the TMSPE, we have our wifi problem - the wifi signal status (which measures packet loss) on the EXP app jumps all over the place, and the top status light frequently goes to RED/offline. This is true both in flight and in front of the hangar, whether or not the engine is running, and even with the EFIS, transponder, and radio off!!
• Unplugging the USB cable from the EXP unit restores the EXP wifi signal to 100% or thereabouts, and it stays reliably connected to the EXP configuration app and ForeFlight.

Why might the USB cable be doing this? Any suggestions on how to address the interference?

I have a similar set up as yours. The NW 600EXP is mounted on the fuselage side wall Except just behind the pilot seat. The Xponder antenna and TRNSMSPE is forward and right under the copilot seat . Don't remember how long the USB cable was maybe 6 ft. The Wifi antenna is" on top " or "up" as the 600 exp is mounted, using a Garmin 327 ( yes I know is has a RS signal wire) . I have experienced several occasions of losing the wifi but not so much as being a problem. I'm using the wifi to a IFly 720 only. Sounds like your USB cable may be a bit longer than mine. Curious as to what the problem may be keep us posted.

Still no fix, though some clues. We bought another 10' USB extension and plugged it in on both ends without routing it. We got a better wifi connection to the iPad app initially and then tried moving the cable around (testing with the plane outside the hangar).

We couldn't get the wifi interference consistently, but it seemed that when the USB cable ran near even low power wiring, we sometimes had problems.

But even changing the routing again to maximize the USB cable's distance from other wires where possible, the wifi works fine in the hangar...but still has the interference problem as soon as we pull the plane out.

We'll try flying again when we can to see if there's any improvement from last time.

I'm forwarding this thread link to Bill at NavWorx so he is sure to see it. With my app it will show connection status as a % of good packets vs badly formed packets. The status color will drop from green to red based on a number of factors so going red alone does not mean you've lost your connection, but does mean that some requirement for that data to be considered valid has not been met. This can be from bad data delivered by the transponder or EFIS in addition to a possible connection issue.

Doug, thank you for continuing to hunt this down. Your routing hint might be a valuable clue for Bill. For the record, most installations have proven to be very reliable and robust.

What kind of low power wiring were you near when you had the lowest % connection?

The wiring we were near included the wires from the Navworx EXP harness, flap motor wires (while the flap motor was inactive or with that circuit breaker pulled), and the ELT switch and antenna. In addition, the forward connection of the USB cable is cable-tied to the transponder cable - this is also where the excess length of the USB cable is taken up in a loop, which is also a potential EMI point.

The current routing has the USB close to other wiring only 1) where the harness and the USB cable leave the EXP box, 2) going through the passenger seat back bulkhead, where the USB passes through close to the flap motor wiring, and 3) when the USB descends through the passenger seat pan and is secured to the transponder cable.

It would be possible to remove the excess USB from the forward area near the transponder and relocate it aft (but it would be helpful to know in advance that foreward is positively a place to avoid excess USB cable, because relocating it for another test would require taking the seat pan and possibly baggage bulkhead covers off again).

I do remember that all the excess in UBS cable is looped at the EXP unit in my case, and looks like the UBS is pretty much by itself all way back to the Exp unit. Looking back on the order confirms that my UBS is 6 foot. FYI

More testing

Hang in there, Doug. I did a few hours of testing today and am adding some more telemetry to the app so I can catch every instance where any dropouts occur to emperically evaluate each change I try.

Thanks for the update, Neil. Getting detailed feedback from the app that way may help hone in. We flew today - the first flight since our adjustment of the cable last weekend which has a little more excess USB up front near the TransMon and transponder antenna, but with the USB not bundled to any other wires.

The FAA report showed no (red) failures, but 8 for max consecutive failures of the altitude encoding. Hard to tell if that's just the scarcity of ADSB towers out here, though. In the cockpit, WX and traffic worked fine on the EFIS, but wifi was in and out as before.

Navworx EXP wifi now working

Our EXP's wifi has now worked correctly for the last two flights.

It appears that moving the USB cable away from the other wires (EXP harness, ELT antenna wire, NAV light wire) in conjunction with rotating the EXP wifi antenna 90 degrees made the difference.

Either one of those by itself hadn?t been enough to fix the problem in earlier testing.

Thanks, Neil (AllThumbs) for your followthrough and support!

You're welcome, Doug! I'm glad that's all it took. I am still working on some improvements to the app to get more data, support track-up traffic in flight, and possibly push out the amazing apple watch extension that I KNOW you've all been waiting for! (irony intended)

I looked at pics of Doug's install and noticed the WiFi antenna was parallel to a large metal surface. I had a hunch it would work better when oriented 90 degrees to the mounting surface.

Since the wifi antenna is connected to the 600 exp. Wonder if the appropriate coax extension could place the short wifi antenna to a more favorable location ??

That is certainly possible. I actually bought an extender for an RV-12 install (documented elsewhere on VAF) but did not use it as the signal strength seemed fine. I do think that getting the antenna closer to the cockpit might help some with updates and plan to relocate the -12 antenna next time they give me access to the avionics bay.

Here's what I bought: https://www.amazon.com/DHT-Electronics-coaxial-assembly-female/dp/B00COJWS32

Navworx EXP wifi - update

The mysteries continue with our EXP unit's wifi. After working well for a few flights, our unit reverted a few weeks ago to its errant behavior. We verified the wifi antenna hadn't moved.

Our symptoms are these:

• It's only rarely that the EXP wifi connects well (all green) to the iPad app (though admittedly, we wouldn't generally use that in flight, except for testing)

• Traffic sometimes fails to update for awhile on the iPad, though the MGL EFIS keeps displaying the ADS-B traffic correctly

• The "secondary" (GPS?) altitude on the iPad app is very unusual - frequently thousands of feet low, sometime even negative

Otherwise, the unit is working well for us - the EFIS display is very helpful, and we've gotten clean reports back from the FAA ADS-B test. We're running iOS 10 and the updated version of Neil's iPad app.

At some point, we may consider trying to relocate the wifi antenna forward of the baggage bulkhead cover (using an extender), but I'm not sure that would help. When we do have connectivity with the iPad app, it shows the signal strength usually in the high 90's, up to 100%.