Another 'any idea what this is??' Thread!!

Due to a completely un-readible site plan of the former RAF Leicester East, i made a completely pointless 'voyage' through a load of unforgiving nettles and thorns thinking i'd found the battle Headquarters...Typically it turned out to be some sort of disused concrete cattle feeding 'thing'....Looked just like a BHQ in the distance though Grrrrr!!!
Anyway on the way back to the peri track i found this small section of concrete hidden away in some long grass. It's situated not far from the where the tech site was. I can just about make out the words petral instillation on the plan to what i think the number matches up with, but the print is so blurred and poor i can't say for sure. There was defitnetly a picket post nearby. Any ideas?? -

maps.google.co.uk/maps?client=firefox-a&...642&t=h&z=19&iwloc=A