Short Shielded Receiving Loops

Been thinking of this for some time. I have a length of surplus LCF12-50 feeder that simply is never going to be used for feedline again, as I cant afford the connectors. So why not use it for something else?

Surplus hunk of LDF12-50 1/2inch feeder

One obvious use is a loop antenna. The solid outer shield lends itself well to being used as the E-field shield of a 'magnetic loop', if of course we discount the practical issues of cutting the stuff! I have been contemplating making a clone of the Wellbrook loop antenna with it, but, the Wellbrook is a balanced loop, using just the 'pipe' its formed from as the antenna, in this case that would be the shield of the feeder, meaning the inner conductor would be redundant. At present this seems a bit of a waste, as there are other designs that would make use of all of the parts of this rather expensive cable!

So, Im looking at the Short Shielded One Turn Loops, as per PA0FRI/PA2GZKs designs.

So, after removing the manky PVC tape and the old cable markers, I roughly rolled the LDF12-50 out and measured off an approximate loop with a 120cm diameter. On cutting this section off from the remainder, I found that the left over section itself is near bang on for an 80cm loop!

120cm and 80cm sections as cut

Now, I have already used about 6 inches of the LCF12-50 to form the handle of a VHF DF loop, which is in the testing phase. This is another version of the loop I attempted way back in 2015.

VHF DF 1/2λ loop with integral 1/4λ sense antenna

The plan is to form the loops, and then use an 'off the shelf' LNA with them for initial tests. 120cm is a pretty big beast, so a comparison of performance between the 120cm and 80cm loops will be interesting. My main interest for these is in MF and LF work.

With the pieces cut, the next job is to prepare the ends for connection, and to remove the central section of the shield to provide the break in the shield loop. As the shield loop is continuous at the feed point, this means I will have to sacrifice a small section to be used to rebuild the shield at the feedpoint, maybe a couple of inches. As this is fairly flexible stuff, there is no need just yet to form it into a perfect circle, which will require a bending jig to be built.

Unfortunately, on measuring the actual length for the 120cm loop, I found I was a little short! I could have made a 114cm loop, but didnt like the idea of the 'odd' dimension. So, instead, I will cut the length to 345.5cm, for a 110cm diameter loop. This also gives me plenty of offcut for bridging the gaps of the feedpoints.