1090 congestion shouldn’t need to be an issue if you use low power for GA purposes. The 20W used by SkyEcho is perfectly sufficient and with even lower power outputs then there is plenty of capacity on 1090 unless we all fly about in close formation!
The biggest problem for 1090 is the continued insistence on using transponders that output at 500W, 250W and even the lower power 125W Class 2 transponders. It’s crazy using ADS-B Out with those sorts of power levels for GA as who wants to track my aircraft flying over Newcastle with a receiver based in London!
That is why CAP1391 is a great initiative and the whole idea of a Low Power ADS-B Transceiver (LPAT). In fact in 2014 the UK’s QinetiQ did such a peer reviewed study called “Low Power ADS-B Transceiver (LPAT) RF Environment Modelling Study”. The conclusions of which mean that low powered units would not need to suffer the spectrum congestion problem that others talk about.
The biggest problem for 1090 congestion is the ‘willy nilly’ interrogation on 1030 by TCAS, SSR and Military Interrogators producing lots of replies on 1090 - many of these being 250W or more from multiple sources. Removal of the older Mode 3/A transponders and using ADS-B for collision avoidance rather than a 1030/1090 set up for TCAS would really help. The US’s insistence on keeping Mode 3/A means that they had to open up 978 for their GA ADS-B solution, but the use of LPATs as per CAP1391 expects that this would not be necessary. TCAS/ACAS is a big offender as well to adding to frequency congestion - Hybrid Surveillance using ADS-B has already demonstrated that it produces much less spectral congestion.
I often liken the 1090 debate in my thoughts to that of ‘Project Fear’ in that it is often quoted to be an issue to those that really do not understand what is the root cause of the problem - that frightens them unnecessarily in my humble opinion.
Yes, independent studies and trials are good. It would be great to hear from the scientific community on the effectiveness of the various EC devices rather than from their various sales teams!