Author Topic: 24 khz spike seen  (Read 775 times)

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Offline n2qew

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24 khz spike seen
« on: September 12, 2014, 09:59:30 AM »
Here's an odd one for those in the know....
I'm running my station on auto. The server pushes the gain wayyyy up when there's not any local signals. Spectral analysis of signals shows a spike at about 24 khz. This is a really low level signal, and it's out of phase and approximately equal between the two channels which leads me to think whatever the source is lives diagonally from the antenna. I haven't gone looking yet.
http://frankfortweather.us/BoStaSig/lela1156/index.html

The question: Is there any posibility that what I am seeing an actual VLF transmitter, like Cutler Maine? I see a similar signal on the Groton, CT site, which is close to Maine.
http://frankfortweather.us/BoStaSig/grot982/index.html


Offline Einar

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Re: 24 khz spike seen
« Reply #1 on: September 12, 2014, 10:22:43 AM »
In another post you show a lamp modified to use LED.
Did you check whether this lamp have some connection with your 24KHz?
LED drivers PWM are switching at frequencies that might well be around there.
If it is close to your BO hardware it may be the source of interference.

Offline Cutty Sark Sailor

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Re: 24 khz spike seen
« Reply #2 on: September 12, 2014, 10:35:32 AM »
Yes, it could be VLF sub com... it's in the right freq band... and anything Navy could be happening to your N,S,E... :-)
though your spike appears to be approx. 1-2 kHz higher than Grotons... it's really difficult to pinpoint exactly with those FFT image transformations.... but there could be one of many 'mobile' com sites nearby, temporarily....    does anybody think the Navy relies on a handful of fixed targeted transmitter sites?  ;)
« Last Edit: September 12, 2014, 10:40:07 AM by Cutty Sark Sailor »
 

Offline n2qew

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Re: 24 khz spike seen
« Reply #3 on: September 12, 2014, 11:10:08 AM »
In another post you show a lamp modified to use LED.
Did you check whether this lamp have some connection with your 24KHz?
LED drivers PWM are switching at frequencies that might well be around there.
If it is close to your BO hardware it may be the source of interference.

I think you are talking about the guy that replaced the circuline fluorescent bulb with the LEDs. Not me, but cool idea. Anyway, I do have a number of LED lamps, and some CFLs (not many) in the house. The antenna is far - about 80 feet - away from the house, and 60 feet away from the shed where the controller is. To check for local interference, I killed power to the house, and dumped the UPSs. Blitzortung controller uses a wireless bridge client (tested, and does not radiate), which was redirected to my wireless hotspot on my phone. That and the Blitzortung equipment was powered from a battery during that time, with the 5 volts supplied by a power trends isolated regulator - does not radiate much, and actually switches at about 500 khz.

There's really not much there, and it's only evident when the gain is set really high by the server. I am able to receive strikes far away. I was really wondering if it was possible that I was receiving some VLF transmitter.
One thing I did notice in testing is that the Vee generator causes just a little bit of 1khz tone to be induced into the output of the amplifier. I have the display set to timeout after 15 seconds, so that goes away.

Offline JonathanW

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Re: 24 khz spike seen
« Reply #4 on: September 12, 2014, 03:11:21 PM »
I've run across signals like this from CFL's, as well as possibly certain flat-panel TV's.  Right now, that signal for me mostly comes in because of the multi-megawatt submarine comms transmitter in Maine (which you mentioned).
« Last Edit: September 12, 2014, 03:13:09 PM by n0ym »