Odd ADSB USB problem

[Seanhump]

Afternoon all ..

Can anyone shed any light on this for me ..?

More of the kit has arrived today for my all-in-one case ...

I've set about connecting things up to test for fit and positioning and have come across the following ..

With the ADSB dongle hooked up to the correct port on the Pi with the supplied whip antenna, all is fine (shows as connected on the home screen, GREEN and receiving messages and updating skydemon correctly with traffic. - All is good

With the ADSB dongle hooked up to the correct port on the Pi with the Nooelec 1090 Mhz antenna connected via a short pigtail, all is fine (shows as connected on the home screen, GREEN and receiving messages and updating skydemon correctly with traffic. - All is still  good

As soon as I put the ADSB dongle , (with a pigtail and NooElec 1090 MHz antenna this time) on a short (approx. 4 inch) USB extension, ADSB drops out - the home screen shows the dongle is connected, but RED with no messages.

If I replace the NooElec antenna with the whip antenna (still with the ADSB dongle connected via the USB extension) it springs back to life

I have tried this with  several different  SMA MCX pigtails (several came with the NooElec antenna, plus some others I had) - no difference made

I've tested the USB extension on a couple of PC's - accessing USB memory sticks etc etc and all is fine there ....

Have to admit to being slightly baffled .. (the short USB extension is a left angled one so that I can move the ADSB dongle to a move suitable location in the case ....)

Thanks in advance

[Paul_Sengupta]

How odd. Could it be that there's some sort of interference which is exacerbated by the little USB extension, and with the pigtail it gets picked up, causing a degradation of signal?

[Seanhump]

That's about the only thing I could think of too.

I'll have a poke around for a shielded USB extension and see if that makes any difference

Thanks

[Ian Melville]

Did you get some copper tape with your NooElec antenna?

I did, and have doubts that they are end fed dipoles, therefore need a ground plane. The Pi and Dongle may have been acting as a ground plane, which will be lost is you use a USB. Extension?
Does not explain why it works with the original whip on a USB extension 

[Seanhump]

No tape supplied - just the two antenna's and two pigtails ....

[Ian Melville]

Try making a ground plane. Plue Peter style bacon foil and sticky tape

[Seanhump]

Will do..

[exfirepro]

Sean,

I would be very surprised if the presence or otherwise of a ground plane will make any significant difference to the reception of relatively high power ADSB signals.

Parts 1 & 2 of your test proves that there is nothing wrong with the NooElec (or whip) antennas, pigtails or SDR Dongle as in both cases the dongle is showing as connected in the Home Screen and traffic is being detected. With Test 3 it could just be coincidence that when you changed the NooElec antenna with the SDR dongle onto the USB extension the ADSB traffic temporarily disappeared and there was no longer any ADSB traffic about. If no ADSB traffic has been received in the last 5 seconds (IIRC correctly), the ADSB ‘light’ will change from GREEN to RED even though the SDR dongle is still showing as ‘Connected’ - exactly as you describe. By the time you replaced the NooElec with the whip again ADSB Traffic may simply have re-appeared.

To prove or disprove this, you will need to run the tests for longer, preferably in a position where the antennas have a clear view of the sky in the direction of known ADSB traffic - try confirming the presence of local traffic on Flight Radar 24. Test 4 would certainly seem to confirm that the issue is NOT with the USB extension as you got traffic again when reverting to the original whip with the SDR still on the USB extension. As I say, possibly simply coincidence.

It doesn’t by the way matter which port you connect the SDR dongle to, provided you don’t change any of the port settings from ‘Auto’ on the Configure Screen, though the recommended ports have been found to be the optimal placements to minimise physical blocking between the modules.

By the way, probably not the case here, but be careful when using pigtails other than the ones supplied with your antennas as they could be what is known as ‘Reverse Polarity SMA’ - which means there will be no centre pin and hence no connection between the antenna and the other end of the pigtail even though they will physically screw together (though it doesn’t sound like this is the issue here).

Regards

Peter

[Paul_Sengupta]

Reverse SMA pigtails will have a centre pin. Unfortunately, so will a "normal" SMA antenna, so it won't fit! Normal SMA pigtails don't have the centre pin, so the problem comes when you try and use a reverse SMA antenna. Then there will be no pokey bits sticking out of either end.

[EricC]

If I remove the ADSB aerial from the dongle and reconnect, the PAW does not
receive ADSB until the PAW is rebooted.

[exfirepro]

Interesting, Eric,

I hadn't thought of that. Not at home at the moment, but will try one of mine later when I get home. If that is 'standard' it would certainly explain the issue.

Yes Paul, of course you are correct re the SMA / RP-SMA connectors, I was just trying to indicate the general principle in case it was an issue, though as I said, I thought it unlikely.

Regards

Peter

[Paul_Sengupta]

If I remove the ADSB aerial from the dongle and reconnect, the PAW does not receive ADSB until the PAW is rebooted.

Yes, I also found this. I think at some point Lee made the ADS-B dongle hot swappable though, so maybe unplugging the dongle and plugging it back in again might work rather than having to reboot the Pi. Not sure though, haven't tried it.

[EricC]

Just tried it.  Mine is not hot swap able, requires reboot.
The dongle is the long blue one.....drilled lots of holes for
cooling, not possible to read the makers name.
Found the type.  RTL 2832V R820T

[Seanhump]

Thanks for the input Peter

I'll double check the pigtails with a meter to confirm that they are ok (they did come as a bundle with the NooElec antennas - one for each)

I'm around 7 nm north east of EMA so there's plenty of ADSB traffic around here, plus the usual mix of GA stuff too.

Testing again this evening (no time in the cockpit today due to students getting in the way...!) and will see what I get.

My ADSB dongle is the small black one and IS hot swappable (according to info found on this site - the GPS and ADSB dongles, but not the WiFi one are) - I've been unplugging the dongle, then swapping antenna's over before reconnecting the dongle.

I've seen ADSB traffic come and go, with the ADSB 'light' turning RED when there are no signals in range, then going back to green when traffic comes into range.

The GPS 'mouse' arrived today (works perfectly), along with the P3i antenna extension pigtail and USB solder plugs so just about ready to get it all in one place..

[Paul_Sengupta]

If you're hot swapping, have you tried rebooting the unit?