What brands of radios are these folks using that are having fly-aways?
Are they all using direct sequencing?
I agree that using a spectrometer would be a good idea, but a quality tool can cost around $30K if you want to get reliable readings.
Safest bet is to invest in a quality brand of radio system that has the highest number of FHSS frequencies that you can afford:
https://www.rchelicopterfun.com/RC-Spread-Spectrum.html
