Smooth trace, smooth spectrum - strange
#6
(2017-05-21, 05:32)BobW Wrote: "Something I hadn't twigged about"
Ok... Had to get the Brit to Yank translator out for that one!

Whoops, sorry. "Something that hadn't occured to me before".


(2017-05-21, 05:32)BobW Wrote: So , watching the page on LMO, those pulses happen pretty frequently, so loop peak / null should be able to do it. It looks like they center around 10khz. Dog collar fence, electric fence, lawn mower loop? Power line comms?

My turn. "LMO"?  

<strike that- LMO the onlilne version of the PHP MyBlitzortung that you can run on your own server>

Doesn't that just cycle through the last dozen or so signals showing each one for a few seconds. Without looking at the time stamps you don't know if those dozen or so signals cover an hour or a minute...

The Archives > List might be a better place to look at the signals. Being static you get a chance to look at them properly. Just spotted some that have that auto scaled Y axis at 2 V! Another feature is many signals have an "echo" approx 250 us after the main signal. 250 us is about 75 km at light speed in free space or 60 km in a cable. I can't imagine what in the world could cause a real, measureable, signal with path length distance difference of 75 km. Unless VLF is reflected by one of the ionosphere layers? But the "echo" is fairly consistent in being 250 to 300 us and it shows on small (100 mV PtP) and the massive 2 V PtP signals.

I doubt the head amp to receiver cable is 60 km long but I'd have a good look at the termination of the screened plugs to screened cable. The cable/plugs I used needs the cables screen drain wire soldering to the plugs screen. There is also something you do (or maybe don't do!) with the input side of each channel of the H-field head amp when using loops. Bridge (or not) a couple of solder pads.
Cheers
Dave.

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RE: Smooth trace, smooth spectrum - strange - by allsorts - 2017-05-22, 10:47

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