What I did in the USMC: Work on the missile fire control system of the F-4J McDonnell-Douglas Phantom Ii

Thread Starter

SgtWookie

Joined Jul 17, 2007
22,226
Ran across this video of a film I'd not seen before; the 1967 flight test/missile shoot of the aircraft type I worked on from '75-'80.


It's been over 42 years since I last worked on them, but the equipment designations came whirling right back.

Fun facts:
The F-4J's AN/AWG-10 radar set had a 1,425 Watt X-band main KPA (Klystron Power Amplifier) for PD, CHIRP and SP modes
(PD = Pulse Doppler (about 50% transmit duty cycle), SP = Short Pulse (0.65uS for 10nm range), CHIRP = a mode where the trigger pulse is expanded from 0.65uS to ~70uS while outgoing, and compressed back to ~0.8uS during receive using a single delay line (basically, an inductor).

There was a 2nd KPA of 900W for target illumination, used with the AIM-7 Sparrow radar guided missiles. You'll see the rectangular feedhorn for the CW illuminator on the starboard edge of the main antenna.

There is a wide rectangular area on the main antenna just above the center feedhorn; this is the "beam spoiler" used for PPI mode (Plan Position Indicator aka ground mapping). When PPI mode was selected on the RIO's control panel, the Beam Spoiler would extend about 1-1/4" to cause the system to spread the RADAR beam vertically.

This aircraft was not equipped with IFF antennas (Identification Friend or Foe) ; a later modification placed eight dipole antennas polarized vertically across the the face of the main antenna in two straight lines equidistant from the center feedhorn.

The antenna had a range of 120° in both AZ and EL.
There were 3 scan modes; 1-bar, 2-bar and 3-bar modes. In 1-bar mode, the antenna scanned one direction, changed elevation slightly, returned the other direction, and resumed original elevation. 2-bar added 2 more elevations; 3-bar another 2 elevations. This helped the RIO scan the skies ahead without having to continually manipulate the elevation thumb wheel.

An interesting tidbit is the safe distance for PD mode on the ground was 175 feet, but for formation flying with cockpit attenuation of 5dB, it was 22 feet.

PD was the most powerful mode of the radar, and was the first airborne radar with lookdown/shootdown capability. However, this model's display was difficult for the aircrew to understand, so many used CHIRP or SP instead. PD mode displayed bogeys in Vc (closing velocity) in a range of -500kts to +1,500kts instead of range; to determine range you needed to lock on to a target. CHIRP and SP modes displayed targets in relative distance.
 
Last edited:

Ya’akov

Joined Jan 27, 2019
5,998
The reason I remember the F4 is that the Blue Angels flew them. When I was a kid in the 70s, the Blue Angels were kind of like the SEALs of the air in the popular mind, sort of superhuman performers in a military context. I once got to see the Blue Angels but racking my brains I can’t remember the context. It must have been an air show becasue there were other planes. It was not a regular thing for my family to attend air shows, though.

This is long, but with a lot of information and flight footage.

 
Top