We are monitoring atmospheric VLF's via a large coil and would like to do away with the hardware low pass and 50Hz notch filters.
Since the amplified signal is being observed on PC anyway, is there any commercial software that will perform the above function while still allowing the filtered signal to be viewed in real time?
Ken Leader
Several real time filters here:
On a sunny day (Thu, 19 Nov 2009 03:06:41 GMT) it happened snipped-for-privacy@estrech.com (Ken Leader) wrote in :
There are software filters for on the PC.
Much of the software for ham radio using sound cards will do what you want. Start with googling "ocky sdr ham softrock"
Steve
Depending on how big the 50 Hz is, you can pay a lot in dynamic range for the convenience of filtering after digitizing.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Typically when you do a system like this you want to filter somewhat (or a lot!) going into the analog to digital conversion -- your 50Hz signal is going to be HUGE compared to anything else, which means that you'll have to seriously reduce the gain going into your PC to avoid clipping, which means that you'll seriously reduce your signal, which (since your PC's A to D conversion introduces noise) means your SNR will go seriously down.
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If you are interested in the atmospheric phenomena, you should stay at least in few hundred meters from power lines.
Then the observed signal consists mainly of EMI created by PC.
It is not big deal to make a filter which cancels AC frequency and its harmonics, still man made EMI will be dominant at the frequences up to
100kHz or so.Vladimir Vassilevsky DSP and Mixed Signal Design Consultant
Many years ago (BC, before CAD schematic capture), I did a design for Lightning Location and Protection (Tucson), for a network of small airports to track thunderstorms.
I don't recall any VLF involved. However I'll dig thru my paper archives and see what I can find. ...Jim Thompson
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If you sample synchronous to the power line frequency, a simple comb filter would notch it.
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