This second part covers the Pulse Doppler radar mode, Notching and Pulse radar mode.
As mentioned in the first part, this is more a collection of tips and ideas rather than explanation. Details are, as usual, in the manual.
III. Radar clutter: Pulse Doppler
(Warning: ludicrously massive oversimplification ahead!)
The Mainlobe is the lobe containing the highest power. The Mainlobe clutter is caused by unwanted returns in the mainlobe and usually occurs when the mainlobe intersects the ground. The Sidelobe clutter occurs when the energy is reflected from directions outside the Mainlobe, usually due to ground returns.
The MLC region is 266kts wide (VF-14 ±133kts), centred around the F-14 ground speed.
The usage of the Mainlobe Clutter Filter can be altered by the RIO by means of the relative switch placed on the left of the DDD. The MLC switch has three settings: In, Auto and Out, default setting is Auto.
The MLC is automatically disabled if the antenna elevation angle is greater than 3°.
As notching targets are filtered by the MLC due to having zero relative speed, the RIO can manually disable the MLC in order to reacquire the target.
Plate 3.2 shows the Mainlobe Clutter filter disabled and the Mainlobe clutter trace displayed on the DDD.
Disabling the Mainlobe Clutter Filter in a non-lookup situation causes the AWG-9 to consider ground clutter as legitimate returns from targets, hence creating multiple false contacts on the TID (this, apparently, is not fully implemented yet so it is theoretically possible to fly with the MLC off most of the time but this creates very bad habits).
A technique the RIO can employ when dealing with defending targets is commanding the pilot in a dive right after cranking (Plate 3.3). When the F-14 is lower than the target, the RIO can increase the antenna elevation and disable the MLC filter, preventing any notching from the target. This allows the WCS to maintain a valid soft lock and guide multiple AIM-54 to their targets.
IV. Recognizing a Notching Target
Plate 3.4 shows how a notching target appears on the TID. Generally speaking, when the projection of the Velocity Vector is as long as the F-14’s VV, then the target is notching.
The RIO has the job of interpreting the VV on the TID and precede the target intentions by working on the Geometry or other means described in this chapter.
A target about to notch is even more recognizable by means of the DDD (Plate 3.5). Since it is the MLC that filters out the returns of a notching target, the more a contact gets closer to the MLC trace on the DDD, the closer it is to notching the AWG-9 radar (the DDD in PD mode shows closure vs azm).
Plate 3.4 shows a target orbiting in front of the F-14 (in Active Pause). The DDD on the left has MLC filter Out, the MLC trace is visible and the target is clearly turning towards a beaming aspect, proven by the fact that the closure rate is decreasing. As the target passed the mainlobe trace, the filter has been set again to Auto and the target disappeared: it is now effectively notching the AWG-9.
V. Pulse Radar mode
The Pulse Radar mode is an older tech compared to Pulse Doppler Radars. It is retained for ACM and “all-aspect” detection and locking.
The Pulse mode can be used along missiles but only in STT mode. The AIM-7 is forced to CW mode and the AIM-54 is launched in active mode. The missile guidance commands requires in fact PD modes to be sent.
Pulse mode is faster than advanced Pulse Doppler modes and can be effectively employed when the target is notching a missile launch:
- select Pulse radar mode;
- set HCU to RDR;
- lock the target.
The RIO must be proficient in quickly switching from any PD mode to PSTT, in order to counter a notching target. Therefore the RIO must pre-set the Pulse radar range depending on the target, maximising the speed of detection, hence the quality of the guidance (the longer the WCS is not guiding, the more the energy of the missile is wasted).
The STAB switch is a 2-way switch and is located in the Sensors Control Panel and controls the ground stabilization of the radar. This mode is currently usable along any radar mode due to a bug but it should be used with Pulse mode only.
The two available settings are:
The first option (IN) stabilizes the antenna along the horizon whereas the second (OUT) uses the aircraft as reference plane. The STAB switch status is override by the WCS if necessary (PD radar modes).
The STAB switch is useful in two situations: the first is ACM. The STAB OUT option changes the reference plane from the horizon to the aircraft itself.
Plate 4.1 shows two examples of the use of the STAB switch OUT. The horizon plane is represented by the Green dashed line. In a merge, setting the antenna elevation using the horizon is hardly feasible. Whilst in the example on the left a lock is achievable by means of ACM modes (VSL HIGH and VSL LOW), the second (right) is less immediate. A lock in such conditions is achievable with the STAB IN, it is much faster in a dynamic scenario, using STAB OUT and simply lower the antenna a few degrees depending on the range and the distance of the target.
The second scenario where STAB OUT can be successful is the lock of target flying much lower or much higher than the F-14 ( ΔALT = ALT F-14 – ALT TGT).
Plate 4.2 shows the antenna elevation angle as a function of altitude (abscissa) and range (ordinate). Values are from my Antenna Elevation model. As the target gets closer and the ΔALT increases. In such extreme cases the RIO may command the pilot to dive, switch to STAB OUT and acquire the target.