With the Jamming Assessment Aerial off it was decided to dismantle it rather than just paint it and that caused us to want to analyse how it worked; a couple of notes first:
- The two aerial elements (dipole and director) are on a shaft that is offset by about three degrees from the centre line so the dipoles rotate in a small circle to emulate the dipole in the missile which is seen below.
Here is the aerial broken down to its invidual parts.
The dish itself is within the drum so the aerial assembly passes through and bolted up to the back of the dish.
- The motor’s gear wheel seen here but the grease has not been dislodged from the wheel apart from where it touched a mating gear tooth. Does this mean that the aerial had not rotatated since it was last serviced, I think it does?
A couple of other observations: Corrosion is affecting the butted alloy joints, so that will be treated. The second being, the drive to the dipole shaft uses a rubber band. It was a check (six monthly?) to ensure the band hadn’t broken and I remember finding at least one that had snapped. The band on this aerial is OK burt set in a shape that again indicates it has never been running.
The diameter of the dish is 16” (just over 40 cm) and is covered in a fibreglass case. It was noted that the displacement of the dipoles from the centre line is the radius of the metal disk in front of dipoles. If you spin the aerial the edge of the disk appears stationary at the point where the disk edge matches the centre line.
A description which looks very close to our arrangement is described here: http://armymunitions.tpub.com/mm50058/mm500580227.htm
Besides the poor soldering a couple of features took us by surprise. First all elements really are electrically connected – zero ohms, even the dipole and director! Also the size of the balance weight is quite staggering.
Here is the schematic of the aerial system, the idea of the offset aerial is shown :
Pete H may connect up a mains supply to see if the motor still runs. If that’s OK he will run the motor again when reassembling and video the aerial rotating.