LF: Re: Re: Strange signal

["Gary - G4WGT" <g4wgt@tiscali.co.uk>]

Hi Marcus,

 

Thank you for your comment....

 

I have not seen a signal derived from a motor quite as stable as this one is, but since you qualify that with your description you may be correct.

 

When I have monitored VLF I have seen our laundry washing machine operate & it is a very unstable signal. Of course ours is quite old now & many modern machines have very complicated control systems & direct drive motors etc.

 

Interesting observation.....I have looked back at my recent captures & note that the "signal" on 474.750 kHz has only appeared since 1430z today during & after our next door neighbour has had a new central heating boiler installed.

 

You may have noticed the other rubbish in the upper part of the display on the full screen shot, I suspect a neighbour has recently purchased a new TV or similar digital equipment.

 

73,

 

Gary - G4WGT.

 

----- Original Message -----

From: Markus Vester

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, January 08, 2013 8:27 PM

Subject: LF: Re: Strange signal

Hi Gary,

 

reminds me of those pretty little asterisk- or spider-shaped artifacts which occasionally appeared on MF and were discussed on this list a couple of years ago. I think the most plausible explanation we found was the acceleration of a brushless synchronous motor. The chopper fundamental frequency might be generated by a digital PWM controller having a stable crystal clock, and the variable sidebands are due to the rotor angle rate dependent modulation.

 

Perhaps this one is similar? Maybe a modern laundry machine or dishwasher coming up to speed, overshooting a while, and then settling on the preset rpm rate. 

 

Best 73,

Markus (DF6NM)

 

 

----- Original Message -----

From: Gary - G4WGT

To: LF Group

Cc: rsgb_lf_group@yahoogroups.co.uk

Sent: Tuesday, January 08, 2013 8:26 PM

Subject: LF: Strange signal

Hi All,

 

I am seeing a strange signal centered on 474.750 kHz. It is periodically visible & audible on my grabber system & my JRC NRD-345. there appears to be no data, just continuous tones. Both systems using separate antennas.

 

I have placed a capture on Dropbox of the grabber image & you can see the end of a previous period & the start of a new one. The signal pattern starts with a bulge at the beginning but just shuts off at the end.

 

https://dl.dropbox.com/u/15990181/472-479-1301081910.jpg

 

I have also placed a capture from the JRC Rx with SpecLab running at QRS01.

 

https://dl.dropbox.com/u/15990181/capt1301081909.jpg

 

Any ideas or knowledge of this signal ?

 

73,

 

Gary - G4WGT.