Pictures of the recently (2014-07-04) rebuilt loop antenna. The loop area is about 20% greater and increases the sensitivity by a useful 1.5dB.
The loops are 'low profile' rectangles to comply with a height restriction agreed with the farmer. They are 2.3 metres high and 13 wide.
The loops are very well matched despite the uneven ground: 375uH and 376uH. A 12kV power line in the background and in the far distance one of the two 33kV lines which deliver power to Todmorden in the valley below.
The antenna cable is slack, all the tension is on the rope and the wire just hangs from that. The cable is 3-core heavy duty mains cable. The house is beyond the tree.
The lower legs of the loops are buried a few cm. The ends of the loops meet up at the center of the antenna, under the white tub which contains the electronics. Signals travel to the house via a buried armoured cat5 cable.
The posts are tanalised fence posts. They are not set into the ground, it is too soft and they would gradually sink. They stand on stone tiles and there is enough downward force from the guys to hold them in place.
The antenna is on a hillside which distorts the loop response. This has to be corrected in software if I want accurate bearings.
Sheep are a problem. I have to use steel wire guys because they chew through ropes. They never chew the white cable.
The loops are aligned N/S and E/W to within one degree, by lining the posts up against convenient distant features.
The next phase of development will probably be replacement of the 3-turn loops with 12 turns which will enable optimum noise performance to be obtained without the input matching transformers. I expect about 3dB improvement in sensitivity. It will probably need a central post to support the weight of the extra copper.