Topband: Pixel Technologies Magnetic RX Loop

[W2PM]

I have actually heard several people - some very experienced 160 DX'ers observe that the magnetic loop can null noise without facing the null to it by raising it's height.  K2DSY said he found elevating it to 3 - 4 ft high at the base seemed to be best for him but then someone else said they picked up more hash there and felt having it at ground level was best.  That could be something relative to the E field rejection perhaps...   IN dealing with very intense power line noise over the past 2 years with some ARRL people - we notice electrical crud off elevated power lines however seem to have odd phasing zones with at the same height of the monitor the noise varies in intensity wildly along a 50 ft section.  I have notices lobes vertically too listening with a sharp, 400 mhz Yagi.    So this whole issue of dealing with very local strong electrical noise may be a science in itself too.  In general, my experience is a properly placed noise sense antenna in the near field of the tx antenna and an MFJ nuller, can nearly eliminate the noise.  My experience with the mag loops was that the null was so sharp even slight physical movement of the antenna in the wind was difficult..    I also have some pennants and flags installed far off the property in the woods surrounding my rear yard with the backside of those antennas to the line... The noise is still there, but again I'll pair the flags with the MFJ nuller (and also have several sense antennas to switch from) ...    

Im in a suburban community in northern NJ with large lot sizes and fairly wooded, and even local electrical service is buried BUT there is a 69KV transmission line running out back at 75 ft high.  Believe it or not, for many years that line was very quiet but they reconductored it a couple of years ago and replaced some insulators which use different wire clamps.  We have pinpointed 3 right to the bolt on the tower with ARRL lab equipment - the aural parabolic microphone - but the damn power company has only replaced 2 of the 3.  That made the MFJ nuller possible because it eliminated the multiple sources BUT if they simply replace the last insulator clamp I'd be "home free".  Waiting now for the Federal Communications Commission to enforce their order from last Fall to fix it ... !

73 Pete W2PM

Sent from my iPad

On May 10, 2011, at 8:07, "Andy Ikin" <andrew.ikin at btopenworld.com> wrote:

> Pete W2PM wrote on the 9th May,
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> "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."
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> 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.
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> 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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> 73
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> Andrew 
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