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Default DIY HF loop antenna queries

Technical questions here, but I'm sure someone knows the answer. I
recently built a 1 meter diameter three turn loop antenna that is
resonated with a broadcast band air variable cap and coupling loop. By
switching in the additional loops, I can get coverage from about 1- 20
Mhz, but I have a couple of questions:

1) I have a small Select-A-Tenna. This is about a one foot diameter
enclosed commercial loop that has probably 50 turns of enamel wire and
resonated by bb cap. It is simply brought near any AM radio that has an
internal ferrite rod, or coupled if the radio has an external small
loop. On AM Broadcast, this small loop seems to do better "honing in"
to stations than the one meter loop I just made, any idea why? Only
thing I can guess is that the many multiple stacked turns of the smaller
loop offer more directionality than the 3 turns of the big loop I made
(and these turns I did NOT stack, just fed through PVC pipe until I had
three turns).

2) Select-A-Tenna won't cover this, but the big loop I made, as I said,
covers 1- 20 Mhz. However, I notice that the sharp increase in the
receiver as I tune to resonance on the lower frequencies (mainly 5
Mhz), gets more and more difficult to notice as I tune higher. On 15
Mhz, for example, I find myself having to turn on my signal generator
and peak tuning with that because the increase is only nil. Any idea

Thanks in advance for your responses.
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