References: <BANLkTinhaEVLub3uu64PWWT1ZyZK6ooQyA@mail.gmail.com><4D9DE551.9020508@talktalk.net> <E82700D8-A268-4D54-8613-6CF609C8C7DC@leeds.ac.uk>
To: rsgb_lf_group@blacksheep.org
Date: Thu, 07 Apr 2011 13:20:38 -0400
In-Reply-To: <E82700D8-A268-4D54-8613-6CF609C8C7DC@leeds.ac.uk>
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From: Markus Vester <markusvester@aol.com>
Message-Id: <8CDC35F3F5B6ED8-1384-7716E@webmail-m143.sysops.aol.com>
Subject: Re: VLF: QRM puzzle - why not the same in a split screen on SL?
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Hi Roger, Chris, Eddie,

I am monitoring both slots here, and also often see railway QRM on 8970 bu=
t not on 8976. I believe that this is due to crystal controlled digital mo=
tor controllers, having a relatively stable switching frequency. This is=
 very different from the simple RC (or LC) controlled power converters (no=
tebook power supplies, energy saving lights, etc), which are often hum-mod=
ulated across several kHz.

For example, my neighbour's new dishwasher generates an repeating pattern=
 of very stable lines on 137 kHz. There have been reports of divergent "sp=
ider" structures in spectrograms from controlled moter acceleration.

Should we move the Dreamer's band 6 Hz up?

Best 73,
Markus (DF6NM)


-----Urspr=C3=BCngliche Mitteilung-----=20
Von: Chris Trayner <C.Trayner@leeds.ac.uk>
An: rsgb_lf_group@blacksheep.org <rsgb_lf_group@blacksheep.org>
Verschickt: Do., 7. Apr. 2011, 18:45
Thema: Re: LF: VLF QRM puzzle - why not the same in a split screen on SL?


On 7 Apr 2011, at 17:24, qrss wrote:
  Considering they=20
 originate from a 50Hz source they are strongest at lower frequencies,=20
 rarely climbing above 6kHz but peaks sometimes get to 8.971kHz not much=
=20
 higher..
Yes, but they disappear between 8970.03 Hz and 9876.57 Hz - that's a very=
 small=20
and for anything to knock them out. It's 0.00105 of an octave. If somethin=
g is=20
cting like a low-pass filter, at 6dB/octave/order, it'd have to be somethi=
ng=20
ike a 500th order filter to drop the signal by 3dB.
I agree, it does look strange.=20

3,
hris G4OKW

----------------------
r Chris Trayner
chool of Electronic & Electrical Engineering,
he University of Leeds,
eeds LS2 9JT, United Kingdom
el: +44 113 34 32053
ax: +44 113 34 32032


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<font color=3D'black' size=3D'2' face=3D'arial'>
<div>Hi Roger, Chris, Eddie,</div>


<div>&nbsp;</div>


<div>I&nbsp;am monitoring both slots here, and also often see railway QRM=
 on 8970 but not on 8976. I believe that this is due to crystal&nbsp;contr=
olled digital motor controllers, having a relatively stable switching freq=
uency. This is very different from the simple RC (or LC) controlled&nbsp;p=
ower converters (notebook power supplies, energy saving lights, etc), whic=
h are often hum-modulated across several kHz.</div>


<div>&nbsp;</div>


<div>For example, my neighbour's new dishwasher generates an repeating&nbs=
p;pattern of very stable lines on 137 kHz.&nbsp;There have been reports&nb=
sp;of divergent "spider" structures in spectrograms&nbsp;from controlled=
 moter acceleration.</div>


<div>&nbsp;</div>


<div>Should we move the Dreamer's band 6 Hz up?</div>


<div>&nbsp;</div>


<div>Best 73,</div>


<div>Markus (DF6NM)</div>


<div><br>
&nbsp;</div>


<div style=3D"FONT-FAMILY: arial,helvetica; COLOR: black; FONT-SIZE: 10pt"=
>-----Urspr=C3=BCngliche Mitteilung----- <br>
Von: Chris Trayner &lt;C.Trayner@leeds.ac.uk&gt;<br>
An: rsgb_lf_group@blacksheep.org &lt;rsgb_lf_group@blacksheep.org&gt;<br>
Verschickt: Do., 7. Apr. 2011, 18:45<br>
Thema: Re: LF: VLF QRM puzzle - why not the same in a split screen on SL?<=
br>
<br>


<div style=3D"BACKGROUND-COLOR: #fff; MARGIN: 0px; FONT-FAMILY: Tahoma, Ve=
rdana, Arial, Sans-Serif; COLOR: #000; FONT-SIZE: 12px" id=3DAOLMsgPart_0_=
f64305e7-8275-4713-bde3-a29df0b45a8b><PRE style=3D"FONT-SIZE: 9pt"><TT>On=
 7 Apr 2011, at 17:24, qrss wrote:
&gt;  Considering they=20
&gt; originate from a 50Hz source they are strongest at lower frequencies,=
=20
&gt; rarely climbing above 6kHz but peaks sometimes get to 8.971kHz not mu=
ch=20
&gt; higher..

Yes, but they disappear between 8970.03 Hz and 9876.57 Hz - that's a very=
 small=20
band for anything to knock them out. It's 0.00105 of an octave. If somethi=
ng is=20
acting like a low-pass filter, at 6dB/octave/order, it'd have to be someth=
ing=20
like a 500th order filter to drop the signal by 3dB.

I agree, it does look strange.=20


73,
Chris G4OKW
=20
-----------------------
Dr Chris Trayner
School of Electronic &amp; Electrical Engineering,
The University of Leeds,
Leeds LS2 9JT, United Kingdom
Tel: +44 113 34 32053
Fax: +44 113 34 32032


</TT></PRE></div>
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