Wed Jun 09, 2021 8:18 am
#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.
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.
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.