many of my (former) customers wanted to use these things on HF, mostly from aesthetics or stealth (🙄) aspects. Er! Efficiency? Wossat? 😉
They're not actually designed for transmission! Unless the circumference is a significant proportion (>30%) of the wavelength to be transmitted.
Even then, put significant power into it and you risk burning anyone near it!
Put just a few watts RF power into a small loop antenna and you get kilovolts on the antenna terminals, that's cos the TX current in the antenna is so high. So it needs a large expensive resonating capacitor with a very high breakdown voltage and low dielectric loss.
What you have there looks more like a DF receiving antenna to me.
I trust it is rotatable cos it's propagation/reception characteristic will be two main lobes 180° apart on the axis through the centre of of the circle.
You mention "frequencies it's designed for", what frequencies are you using it for?
I assume shortwave.
Surprised that you have interference from ASDL! Although I realise that ASDL uses frequencies from 26.075 Megs upwards to 137Megs for the Upstream communication ASDL connections are usually screened underground cables which shouldn't bother you!?
Unless there's a fault in the cable or your local distribution box😠
I only came across such loops (or more usually rectangular frame antennas) on board ships as an attempt to reduce the radar signature. Unfortunately at the expense of COMMS efficiency.