Re: VLF: QRM puzzle - why not the same in a split screen on SL?

[Markus Vester <markusvester@aol.com>]

Hi Roger, Chris, Eddie,

 

I 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 controlled digital motor controllers, having a relatively stable switching frequency. This is very different from the simple RC (or LC) controlled power converters (notebook power supplies, energy saving lights, etc), which are often hum-modulated 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 "spider" structures in spectrograms from controlled moter acceleration.

 

Should we move the Dreamer's band 6 Hz up?

 

Best 73,

Markus (DF6NM)

 

-----Ursprüngliche Mitteilung-----
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 
> originate from a 50Hz source they are strongest at lower frequencies, 
> rarely climbing above 6kHz but peaks sometimes get to 8.971kHz not much 
> higher..

Yes, but they disappear between 8970.03 Hz and 9876.57 Hz - that's a very small 
band for anything to knock them out. It's 0.00105 of an octave. If something is 
acting like a low-pass filter, at 6dB/octave/order, it'd have to be something 
like a 500th order filter to drop the signal by 3dB.

I agree, it does look strange. 


73,
Chris G4OKW
 
-----------------------
Dr Chris Trayner
School of Electronic & Electrical Engineering,
The University of Leeds,
Leeds LS2 9JT, United Kingdom
Tel: +44 113 34 32053
Fax: +44 113 34 32032