Yes, im assuming you are asking when enemy aircraft Radar is switched off.
1. Radar Cross section detection through a Surveillance Radar using low frequencies or Track while Scan mode.
2. Intercepting/tracking VHF/UHF comm links and other data links. Voice communication is mostly through VHF or UHF in RF spectrum between pilot and ATC/Command. The monitoring system has to be robust in tracking even short comm/data message bursts.
3. Detecting IR signature of the aircraft using IRST/FLIR.
View attachment 553225
True, seen that in SCO Chinese comm systems deployed in north of Pakistan. Another reason why USA tactical radios were preferred before 786 series of PA radios were provided by NRTC.
Haan emotional ho k share kar dena. nokri se tu bari jaldi farigh honay wala hay in harkaat ki waja se. chup nai reh sakta tu.
You are always spot on