Digital lowpass filter
#1
today I installed the four digital lowpass filters. The noise floor droped from 110mV to 50mV,  Which allowed me to raise the gain to 16X10 with no problem. I`m running in manual mode. I`m testing yet the best value for LPF tune, but seems to be around 50KHz. I have the LPF tuned in 25Khz and monitoring the spectrum but I can`t see advantage  in relation to 50Khz. I have a lot of militar stations in VLF with very strong signals (about 75 or more dBuV) between 15KHz and 60Khz which occupy part of spectrum, but apparently without causing problems.  I`m able to tune and measure this stations on my VLF receiver R&S EK070, with an R&S EH10 active antenna. I also took 4 outputs on the back panel to connect the oscilloscope.
I think the lowpass filters were a good investment, but I have to wait some more time to check the operation.
Shy

Station ID 1846


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#2
Great idea for the test ports!

I may have to do something like that some time.
Kevin McCormick KB0UOI
Macomb, IL USA
Stations: 1539
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#3
That is a very impressive build and construction!
I was rather attracted to this post... apologies if this reply seems condescending or whatever...
Now, do one thing... examine that board very closely, after insertion in the metal case, for any possible
shaving from the 'screw drills' that might be present!

The fact that you've spent some time with 'tracking noise' and with 'effecting resolution' is what this project is all about.!! 
welcome aboard!

 NOW, what have your learned so far?  Lightning  Do you know why reducing filter Bandwidth reduced your 'noise' ? Do you understand why higher freqs might be important for nearby strokes? (even though data may not be used presently.) Why does lower bandwidth enable you to receive more distant signals better?  Shouold the 'lower bandwidth' improve 'near signal detection and location' or perhaps 'diminish' possibilities for such parameters as 'power', 'polarity', etc?  What's a skywave?  What's a groundwave?  What's a spacewave?  What's a 'zero crosiing'?

Yeah, this is a friendly 'teaser'.... You seem pretty sharp... think about it... Rolleyes  Let's have some fun... Idea

Go For it!
Cheers!
Mike
                   TwinHollies WeatherCenter  Frankfort KY, USA
  Americas Operators at Sferics.us
        Stations: 689, 1439
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#4
(2017-06-10, 00:31)Cutty Wrote: That is a very impressive build and construction!
I was rather attracted to this post... apologies if this reply seems condescending or whatever...
Now, do one thing... examine that board very closely, after insertion in the metal case, for any possible
shaving from the 'screw drills' that might be present!

The fact that you've spent some time with 'tracking noise' and with 'effecting resolution' is what this project is all about.!! 
welcome aboard!

 NOW, what have your learned so far?  Lightning  Do you know why reducing filter Bandwidth reduced your 'noise' ? Do you understand why higher freqs might be important for nearby strokes? (even though data may not be used presently.) Why does lower bandwidth enable you to receive more distant signals better?  Shouold the 'lower bandwidth' improve 'near signal detection and location' or perhaps 'diminish' possibilities for such parameters as 'power', 'polarity', etc?  What's a skywave?  What's a groundwave?  What's a spacewave?  What's a 'zero crosiing'?

Yeah, this is a friendly 'teaser'.... You seem pretty sharp... think about it... Rolleyes  Let's have some fun... Idea

Go For it!
Cheers!
Mike
OK Mike
Lest go talk about your questions.  About the reducing the noise, I need reduce the bandwidth below 50Khz because I have strong interference from switching power supply around 55/60Khz! This is my first problem! I live in apartment with 28 neighbors, with a lot of electronic devices supplied by SW PSUs, from celular charger to portable PCs, IPTV BOXs etc. This is the main purpose  for limit my bandwidth. About the importance of high frequencys in detection of the nearby stroks, in my view point is because the electric field is more efective in higher frequencys than the magnétic field. the magnétic fiel tends to spread trought groundwave, and the electric field more by skywave. So, the skywave is a beter way to electrical field and for near stroks. I`m not reduce my bandwidth for detect stroks far away...This is not a DX station This is a lightning detector in a network. I reduce the bandwidth for reduce the desense caused by the strong noise above 50KHz. The most powerfull militar transmitter I can receive is In 52KHz!  In this frequency I have the UK militar station GIY20 and GNY1 with about 80dBuV measured in a rohde&schwarz EK070 receiver. The LPF help with this stations not only with the noise. 
About polarization,  I'm trying to find a pattern. I`m using a dual cross loop and a E-field monopole for receive the two components of the electromagnétic pulse. The electrical field are 90º from the magnétic field, and the magnétic field is normaly horizontal as we know, and are perpendicular to the propagation direction. but some times in strokes between clouds, this  does not seem to happen. From some stroks the pulse seems to be directional, and with irregular strenght and polarization along the path. About skywave, groundwave (and maybe NVIS) space wave, etc, some people  advocate the thesis, of the propagation in VLF and LF is constituted by the wave guide done by reflection in the ionosphere and by earth, by skywave propgation. I do not really advocate this idea, because during the day, the D layer is stronghly attenuating for lower frequencys, and in VLF the D layer kill completly the electric field. During the night, when D layer disappears the skywave appear, and the electric field becomes more important.  If you listen a VLF station during the day, you can`t  find fadding. Any signal is almost constante. This is the proof that the ionosfer not interfer in the propagation mode, and the propagation is done mainly by groundwave. So, for me, the main propagation in VLF is groundwave, and in this lower frequencys, the magnetic field is the most importante component of the electromagnétic wave, much more than the electrical component. When we lowered in frequency the groundwave gain efficiency, and the skywave gain loss!..But OK I have a 15 days participant, and I`m here for learn and study the stroks fenomenas and change ideias about the system. I`m interesting in all points of the Physical and electronic parts. I do not pretend to be just an strok observer. All I can learn are welcome.

Best regards
Carlos Mourato CT4RK Shy

Station ID 1846
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