Topband: Pixel Technologies Magnetic RX Loop

Andy Ikin andrew.ikin at
Tue May 10 05:07:57 PDT 2011

Pete W2PM wrote on the 9th May,

"Andy.  Again, it's the laws of physics which apply.  The mag loop can only 
be sensitive go the magnetic field and less so to the E field only if it is 
very very close to noise source.  That's just the way Nature works.   The sn 
improvement is mostly from the very deep and sharp null. You point the null 
to the noise.  I have seen 20 over S 9 noise go to s1 with cheaply made mag 
loops.  That's very good.  Problem is in an urban and suburban area there 
may be many noise noises so eliminating one may not help.  But it may.  Even 
so the mag loop is sensitive to all signals local or distance in a vertical 
donut shape.  Most DX at 160 and even higher bands comes in at low angles 
and most QRN from lightning etc comes in high angle.  The only way to get 
meaningful and useful performance in a rx antenna is for directivity in the 
right vertical and hortizontal fields.   This is all for DX performance.  If 
you have nasty local crud noise coming from a certain area and it creates s9 
plus hash in your receiver and all you want to work is domestic, the loop is 
fine.  And in some conditions its ok DX.  I worked my first VK with a mag 
loop.  But there's no magical properties for it and if you want predictable 
DX performance it's fine as a single tool to have but I'd not spend much 
money or other resources on it."

Pete, What I have found is that there is still a significant E Field noise 
reduction even when the loop is not nulling the noise. This is not just my 
observation. There are approx. 5000  ALA1530s in current use in the US, 
Europe and Japan. The feedback I have from users experiencing high levels of 
local noise is that in most cases the loop affords a noticeable improvement 
in the s/n.

Your point in increasing the antenna directivity for Dxing is quite valid if 
the local noise is low. Here I use a 2 x K9AYs spaced 40m apart as a 200kHz 
to 2MHz phased array; the antennas are run in anti-phase with a varible 
delayline phasing controller. Interestingly with this array; if I replace 
the K9AYs with 2 large loops I can get up to a 20dB reduction in the local 
noise. However, the reduction in array directivity does make this a non 
preferred option.



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