Topband: Magnetic Loops

[Tom W8JI]

> At best mag loop lowers the noise in two directions drastically - along 
> with any signals in those two spots.  But in the non null areas there are 
> absolutely no characteristics of the loop which are beneficial for DX 
> other than getting whatever you may get.  Also know the loop has no 
> vertical or horizontal directivity except for the two sharp nulls off the 
> end of the loop so all atmospheric noise will be collected by th antenna 
> and your DX will compete I that noise floor for notice.  For most local 
> non DX work in very noisy spots these are great.
>
> If you want DX Id try a MFJ nuller and a k9ay or flag.
>
> 73 W2PM


That is an accurate analysis of a loop. The "magnetic myth", or shielding, 
is mostly Hamlore.

A properly constructed loop is the same with or without a shield, and has a 
pattern that produces sharp point nulls through the axis.

An improperly constructed loop, with or without the "shield", has a messy 
pattern and may not have complete nulls in any direction.

The field response, or field impedance, is only magnetic dominant within a 
small fraction of a wavelength. Very near field noise might be electric or 
magnetic field dominant, it is random. Far field noise and far field loop 
response is electromagnetic without field gender discrimination. In the far 
field (over 1/2 - 1 wavelength), all signals and all smaller antennas look 
exactly the same for field ratios.   This includes noise from distant 
lightning, or signals from transmitters

This is why sometimes loops help, sometimes poorly designed are better than 
well designed loops, and quite often they do nothing at all. Sometimes they 
make things worse. Most are sold by mythology, like homeopathic medicines.

73 Tom