But even when local radars are off then some radars need to be on to detect non emitting enemy threats (Aircraft and weapons). Those radars that are on can be jammed to deny the entire air defence network information about objects operating passively in their airspace. Obviously it will be clear where the jamming aircraft are, but the radar and radio silent objects that may be receiving datalink info or not will be rather harder to detect especially at longer ranges or in bad weather.
I think we didn't understand each other correctly. I talked for the radars on SAM system or in battery, but anyway. IADS doesn't have only early warning radars, but also other passive sensors like Kolchuga, Orion, etc, and a network of visual observation posts. IADS than combine all those pictures and infos in one big picture, which they send to other air defense units and batteries through data link. If battery get a clear picture of air space from higher level, than they don't need to turn on their radars, but just optically track designated targets. You could also use radars, but for shorter period.
I don't think that is true. Most ESM suites are now fully automatic and are designed to kick in when particular threats appear. A heat bloom on the ground and a rapidly approaching object with a heat bloom following it for example will be identified as an incoming IR guided missile... the reaction time for which will be short. Equally the heat bloom of the launch of an AMRAAM from 40km might not be detected, but when it gets to a position 15km from your aircraft with its rocket motor burned out and only the friction heated nose of the missile as an IR emitter it will be the active radar in the nose of the missile that might be the first clue to the threat... a threat that is likely closing at over mach 3. The ESM suite would not be surprised, it would detect the radar signal and its direction and would likely immediately release chaff and if it is very sophisticated it might direct a jamming beam into the chaff cloud in the hope that the home on jam mode of the AMRAAM will direct it into the chaff cloud.
Either way the reaction to a sudden electronic signal will be very fast.
The point however is that Tunguska has a missile range of 10km and a gun range of 4km and I would guess that its optics can detect and track targets at this range except in the worst weather, so the only times it would have to use radar (ie during an engagement) the target it is engaging will not be the much of a threat for long as its missiles reach 10km in about 15 seconds or so and of they do need to go to radar mode for part of the engagement that is not long enough for that target to get the Tunguskas coordinates and fire an ARM. For threats further away the time it will take to find the Tunguska and lock on and fire an ARM the engagement will be over, the radar will be off and the Tunguska will be moving to a new position.
Misunderstanding again. I talked for radar mode for radio guided missiles. AMRAAM is different class with its active radar homing head. When you use optical mode for radio guided missiles, RWR will not detect emission of tracking radar. Missile itself will be detected by MAWS. To secure 100% kill with tracking radar is, that you turn on tracking radar and go to radar mode in last seconds before missile hit target, so plane have very short time to react. On the other hand you could still work optically, just target will try to jam tracking radar.
...& by the way what is photo-contrast guidance system in SA-13??
This is actually day time optical homing head which see a plane as a dark shadow on the bright sky. It works together with IR homing head and in case when IR doesn't recognize plane because of flares, photo-contrast still see a plane as a shadow.