That is definitely not true. Sensitive VHF radio receivers, tuned to transmitters that are located beyond line of site, can very easily detect VHF communicatio

That is definitely not true. Sensitive VHF radio receivers, tuned to transmitters that are located beyond line of site, can very easily detect VHF communications reflected off of a very small airborne target. I can sit in my office with a spectrum analyzer and watch the signal strength of a distant digital TV broadcast station come in and out of view when an aircraft flies overhead. Couple that technique with a DF network and far more sensitive receivers and GPS timing, and building a passive radar to defeat stealth technology become far easier than you think.