Primarily for general aviation discussion, but other aviation topics are also welcome.
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By gaznav
#1851905
@Forfoxake
It does depend on the antennae gain of the ground stations too. As these aren’t standardised, then you will get differing results for each signal type. Whilst size is no guarantee of performance, it can be an indicator. Just look at the difference in design and size - 1090MHz is 27cm wavelength and 868MHz is 34cm - so really the sizes shouldn’t be that different.

Image

The reason why the 1090MHz ADS-B antenna looks less capable is because you have 250W-500W transmissions coming from commercial airliners (where a 13.5cm bent coat hanger would do!), down through the average GA type transponder at 75W to ~175W down to SE2 at 20W. So really, if you want to pick up the weaker SE2 signals better, then a more fancy antenna is needed. Hence the FLARM and PAW antennas look a bit more impressive in size and design.

Also, I should point out that the ADS-B signal/modulation format is less efficient to those used by FLARM/PAW, but that isn’t going to change until the next ICAO agreement comes out for an ADS-B replacement (maybe 10-20 years away?). So really, to put SE2 on comparison without that simple factor of having similar antenna designs and gains, then the comparison is subtly flawed.
kanga, ls8pilot liked this
By Forfoxake
#1852021
The ADS-B antenna in at least of the one of the local ground stations is the same size as the PAW antenna- as large as the PAW antenna in your picture I think. The FLARM one is a bit bigger-as in your picture. I should know because it is in my cottage! I am about to put all on the roof which should improve reception all round.

However, it is clear that the positioning of SE2 is very important, and probably the aircraft type, at least for good ground reception by ATOM stations. Whether this is reflected in air to air transmission/reception is unclear.

In any event, I still think that SE2 would benefit from an external antenna connection (to connect an antenna external to the box, not necessarily to the aircraft!).
gaznav, ls8pilot liked this
By Straight Level
#1852176
gaznav wrote:@Forfoxake
It does depend on the antennae gain of the ground stations too. As these aren’t standardised, then you will get differing results for each signal type. Whilst size is no guarantee of performance, it can be an indicator. Just look at the difference in design and size - 1090MHz is 27cm wavelength and 868MHz is 34cm - so really the sizes shouldn’t be that different.

The reason why the 1090MHz ADS-B antenna looks less capable is because you have 250W-500W transmissions coming from commercial airliners (where a 13.5cm bent coat hanger would do!), down through the average GA type transponder at 75W to ~175W down to SE2 at 20W. So really, if you want to pick up the weaker SE2 signals better, then a more fancy antenna is needed. Hence the FLARM and PAW antennas look a bit more impressive in size and design.

Also, I should point out that the ADS-B signal/modulation format is less efficient to those used by FLARM/PAW, but that isn’t going to change until the next ICAO agreement comes out for an ADS-B replacement (maybe 10-20 years away?). So really, to put SE2 on comparison without that simple factor of having similar antenna designs and gains, then the comparison is subtly flawed.


Although the antenna size difference is quite impressive, the gain difference is only about 3 or 4db and therefore only a minor factor.
What is most noticeable is the difference in output power between SE2 and PAW (or Flarm)
SE2 20W = 43dBm
PAW 0.5W= 27dBm
Flarm 0.04W= 16dBm

So the 'gain' of SE2 is 16dBm greater than PAW. Taking into account the antenna gain difference, lets say 4db, the ADSB 'link' is still 12dBm over PAW, which is 16x more powerful but only manages roughly 1/4 of the range.
Indeed, ADSB modulation is horrendously inefficient and needs 200W of grunt to do the job effectively. :thumright:
gaznav liked this
User avatar
By gaznav
#1852183
ADSB modulation is horrendously inefficient


@Straight Level indeed it is, but until ICAO and all the signatory nations come up with a new agreed standard for transmitting GPS info on an agreed frequency, reserved for aviation use, then it is the only game in town.

I think my posts show the limitations of FLARM, in that any international aircraft visiting UK airspace is unlikely to have a detection capability on all those frequencies. It is also even less likely to detect PAW’s P3i signal as it has very little global penetration in the market (and unlikely to). So we’re stuck with 1090 ADS-B for now until the next agreement within ICAO a and the signatory nations. Even doing something with 978 would help, but not everyone uses that yet - even though there is an ICAO agreement on its use: https://www.icao.int/safety/acp/acpwgf/ ... 0sarps.pdf

If I was a betting man, then 978 is probably where it goes next…
Flyin'Dutch' liked this
User avatar
By Dave W
#1852190
gaznav wrote:If I was a betting man, then 978 is probably where it goes next…


About 5 minutes after 1090 gets mandated.

Perhaps Betfair will do an accumulator.
By HansGruber
#1859357
@gaznav We have an SE2 in our aircraft. It provides a weak and unreliable ADSB. But at least it's something. We saved spending money on a proper ADSB in/out transponder upgrade on our Garmin 330.
EC-IN is provided by PAw, ADSB, gliders, Mode S. All ported in to Skydemon.
It's £300 (the PAw), you get ALL the benefit, you're not reliant on THEM avoiding YOU. YOU see THEM
Cost effective, see more threats, be safer. Good airmanship is about making good decisions... PAw until there's a comprehensive ADSB + FLARM environment. Cheaper, better, safer - get ahead of the curve.

I've been doing other stuff, didn't ya'll know this already?
Are we enthralled by the 'spend money - hope they see you' theory?
Oops, I have a call. cya!
By johnm
#1859505
I saw a few aircraft on Skydemon today but is Skyecho 2 a reliable EC device seeing most traffic? No it isn't.
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