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@btopenworld.com> wrote:
> 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
> pl
us 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.
>
>
>
> 73
>
> Andrew
>
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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