Here is a first upgrade for my ADSB receiver box – GPS precision time. The MLAT position calculation for aircrafts depends on a precise time. While there is already a time synchronization between MLAT receivers in a specific area it is also possible to add a precise time source to improve the calculation result. A GPS receiver is such source when equipped with a PPS (pulse per second) output. The PPS is a signal with a width of less than one second and a sharply rising or abruptly falling edge that accurately repeats once per second with low jitter. The GPS time and PPS signal are then used to sync the internal ntp time service and keep a low offset and jitter.
My ADSB receiver box is another project that I had on the shelf and now finished due plenty of time.
Here is another quadrifilar helix antenna design, this time for ADSB (aircraft mode-S transponder) reception at 1090 MHz. Unlike other antenna types this antenna has a spherical coverage with 120° 3dB beamwidth and estimated peak gain of 4.6dBi at 1090MHz.