160 metre DXers have long used separate receiving antennas to hear weak signals. However the benefits of this also apply on the lower HF bands.
While a shoddily built magnetic loop antenna might not be good for much apart from WSPR transmitting, it can perform well as a receive antenna. This is because signal to noise ratio, rather than efficiency, is most important in a normal environment with ambient RF noise. Loops offer the benefit of having deep nulls that can be used to null out noise if most of it is coming from a single source.
Loops can either be narrow band (like a transmitting magnetic loop) or wide band. Narrow band is good if you want the loop to act as a preselector. This could be useful on the lower HF bands if you have strong AM broadcast stations nearby and your receiver's front end isn't very strong. However narrow band loops require some sort of variable capacitor which needs to be changed if there is a significant excursion in frequency. Wide band loops don't have that constraint but don't offer selectivity.
* VA3STL receiving loop
* VK2TPM 80m receiving loop on crochet hoop
* W1AEX simple broad band receiving loop
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