Okay all!
I bought another one! This time it was called Hwydo AN200, but they’re all the same. This time I’ve learned some very valuable beginners lessons. If you’re reading this having never used one of these before, don’t expect miracles! Secondly, the point of tuning enhancement is very small, you only have to virtually touch the knob to get it right, that is one you’ve found the maximum noise point it will be to one side of that. I found all this out this morning when I had the bright idea of trying it with my Panasonic RF-2200. This has needle type signal strength meter which was key to all! Having found a usable station (none were very good this morning, appalling conditions) I tuned the rotating ferrite antenna to optimum position, and then having positioned the antenna closely at ninety degrees to one of it’s ends, I went ahead and tuned it. I should say that the needle position was approximately mid point, so any deflection would be quickly obvious. Doing this made it clear that the maximum gain point was very small, much smaller than I had imagined it would be. If I’d known how very small this gain point was, I wouldn’t have been so quick to return the other one. I sa an interesting video on YouTube where somebody compared the small ferrite antenna supplied with the (I think) PL-368 with an AN-200 and there was no difference, this surprised both him and me, but of course the loop isn’t restricted to one or two radios. I hope this might be of help to someone. 

Drifter