Hi all

I am wondering if any RF/Flarm wizards can help me. This is beyond my area of expertise/pay grade.

I am having huge issues with a Flarm unit I installed in a parachute operation's drop plane here in New Zealand. Its a Cessna 185 and the unit is installed with 3 external aerials for Flarm send/receive, Flarm receive and ADS-B receive. The GPS antenna is on the glare shield under the windscreen.

There where two reasons for the install. One for the increased glider traffic in the area after a gliding club relocated to down the road and for the flight following on OGN for the owner/operator so he could monitor the aircraft from the ground for his Safety Management System he needs in place for his commercial operation.

The traffic part seems to work ok but the OGN part is completely out of whack. We compared it with a different manufacturers Flarm product which is installed in a ASH 25 M glider. This install just uses the dipoles supplied hanging back off a couple of mounts in the front cockpit and it shows up on OGN out to about 50 km at times on this base station. This 185 installed unit shows up intermittently if at all and is no use for tracking on OGN. I have sent this data to the manufacturer but they haven't replied as yet.

The data streams are from the OGN Base station unit which logs each reception. Noticeably the ASH 25m glider unit is received every second and the variation? of the signal is consistent at 7.47 kHz ish. The dB is also very consistent. (not sure what that shows to be honest) but to my untrained eye the unit in question is all over the place. Either diploe or external aerial makes no difference. Its transmit is random or the variation of the signal is so spread that it only gets picked up when the signal freq is close enough to what the base station will receive.

Dipole in Glider cockpit.
ICAC81857 [ 59/ 62sec] 1:1:C81857 0.0m/s 49.8dB, 0.0bit/packet, +7.47(0.25)kHz *
Time/UTC
204744: [ -40.97271,+175.63299]deg 117m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.47kHz 50.2/63.5dB/0 0e 0.0km 270.0deg +5.3deg
204745: [ -40.97271,+175.63299]deg 117m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.46kHz 50.0/63.0dB/0 0e 0.0km 270.0deg +5.3deg
204746: [ -40.97271,+175.63299]deg 117m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.45kHz 50.0/63.0dB/0 0e 0.0km 270.0deg +5.3deg
204747: [ -40.97271,+175.63299]deg 117m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.45kHz 50.2/64.0dB/0 0e 0.0km 270.0deg +5.3deg
204748: [ -40.97271,+175.63299]deg 117m +0.0m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.46kHz 50.2/63.0dB/0 0e 0.0km 270.0deg +5.3deg
204749: [ -40.97271,+175.63299]deg 117m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.46kHz 49.5/63.5dB/0 0e 0.0km 270.0deg +5.3deg
204750: [ -40.97271,+175.63299]deg 117m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.45kHz 50.2/63.0dB/0 0e 0.0km 270.0deg +5.3deg
204751: [ -40.97271,+175.63299]deg 117m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.47kHz 50.2/64.0dB/0 0e 0.0km 270.0deg +5.3deg
204752: [ -40.97269,+175.63299]deg 116m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.45kHz 50.5/63.5dB/0 0e 0.0km 270.0deg +2.6deg
204753: [ -40.97269,+175.63299]deg 116m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.43kHz 50.0/61.5dB/0 0e 0.0km 270.0deg +2.6deg
204754: [ -40.97269,+175.63298]deg 116m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x03m 00fo +7.46kHz 50.5/63.0dB/0 0e 0.0km 270.0deg +2.6deg
204755: [ -40.97269,+175.63298]deg 116m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x04m 00fo +7.43kHz 49.5/62.5dB/0 0e 0.0km 270.0deg +2.6deg
204756: [ -40.97269,+175.63298]deg 116m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x04m 00fo +7.45kHz 50.0/63.0dB/0 0e 0.0km 270.0deg +2.6deg
204757: [ -40.97269,+175.63298]deg 116m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x04m 00fo +7.46kHz 50.0/63.5dB/0 0e 0.0km 270.0deg +2.6deg
204758: [ -40.97269,+175.63298]deg 115m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x04m 00fo +7.43kHz 50.2/63.0dB/0 0e 0.0km 270.0deg +0.0deg
204759: [ -40.97269,+175.63298]deg 115m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 02x04m 00fo +7.44kHz 50.0/62.0dB/0 0e 0.0km 270.0deg +0.0deg

As you can see this is every second and is very consistent.

Cessna 185 with the external aerial replaced by the supplied Dipole mounted in windscreen area. All avionics turned off and engine not running to minimize RF interference. The 185 was towed from its hanger 300 meters away with the unit running and was then parked in the same position as the Glider was earlier.

Dipole Antenna only
ICAC80177 [ 16/ 4753sec] 5:1:C80177 0.9m/s 26.1dB, 3.6bit/packet, +11.12(3.84)kHz *
Time/UTC
222238: [ -40.97048,+175.63233]deg 80m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 03x06m 00fo +0.23kHz 15.8/18.0dB/2 3e 0.3km 343.9deg -7.4deg !
222655: [ -40.97047,+175.63198]deg 114m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 00x01m 00fo+10.47kHz 15.8/13.0dB/0 4e 0.3km 337.5deg -0.2deg !
222852: [ -40.97050,+175.63202]deg 107m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 01x01m 00fo +9.47kHz 17.2/16.5dB/0 2e 0.3km 338.9deg -1.6deg
222854: [ -40.97050,+175.63202]deg 107m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 01x01m 00fo +9.42kHz 16.0/15.5dB/0 1e 0.3km 338.9deg -1.6deg
223053: [ -40.97174,+175.63183]deg 111m -0.1m/s 2.8m/s 167.3deg -0.3deg/sec 5 01x01m 00fo+14.60kHz 30.0/31.0dB/0 4e 0.2km 316.5deg -1.4deg
223903: [ -40.97283,+175.63288]deg 108m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 01x01m 00fo+13.12kHz 41.0/40.5dB/0 3e 0.0km 270.0deg -12.9deg !
224145: [ -40.97271,+175.63269]deg 109m -0.1m/s 2.5m/s 292.4deg -7.0deg/sec 1 01x01m 00fo+14.58kHz 36.8/36.0dB/0 0e 0.0km 270.0deg -7.4deg !
224338: [ -40.97299,+175.63185]deg 113m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 00x01m 00fo +9.47kHz 15.5/14.0dB/0 11e 0.1km 258.1deg -0.9deg
224946: [ -40.97287,+175.63285]deg 112m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 01x01m 00fo+10.68kHz 32.0/31.5dB/0 2e 0.0km 251.7deg -5.0deg ?

Not very strong and very intermittent. Gets stronger as the aircraft gets closer to the hanger but still not as good as the previous unit.

Replaced the Dipole with the external aerial. All Avionics still turned off etc.

Parked in front of base station. Then towed back to its hanger.
Time/UTC
232702: [ -40.97267,+175.63238]deg 110m +0.1m/s 2.7m/s 265.5deg -4.3deg/sec 5 01x01m 00fo+15.00kHz 36.5/38.5dB/0 1e 0.1km 277.0deg -3.9deg ?
233325: [ -40.97288,+175.63185]deg 111m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 01x01m 00fo +6.57kHz 28.0/25.5dB/0 1e 0.1km 266.0deg -1.9deg
233616: [ -40.97336,+175.63092]deg 108m +0.1m/s 2.6m/s 086.3deg -1.6deg/sec 5 01x01m 00fo+14.64kHz 31.2/33.5dB/0 1e 0.2km 251.7deg -1.9deg
233743: [ -40.97308,+175.63187]deg 108m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 00x01m 00fo+12.50kHz 21.2/20.0dB/0 5e 0.1km 254.2deg -3.3deg
233852: [ -40.97167,+175.63155]deg 108m -0.1m/s 3.7m/s 348.8deg +0.0deg/sec 5 00x01m 00fo+16.55kHz 39.0/43.5dB/0 2e 0.2km 310.8deg -2.1deg
234011: [ -40.97047,+175.63220]deg 112m +0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 01x01m 00fo+10.25kHz 19.8/18.5dB/0 9e 0.3km 342.2deg -0.6deg
234150: [ -40.97047,+175.63219]deg 111m -0.1m/s 0.0m/s 000.0deg +0.0deg/sec 1 01x01m 00fo+10.38kHz 21.2/18.5dB/0 8e 0.3km 342.2deg -0.8deg

Any thoughts or suggestions much appreciated.

Cheers

Paul