Low Pass Filter problems

[allsorts]

Fault moving, know good fitted in original faulty position working, doesn't leave many options other than a duff chip. Not good at not far under £10 a pop.

[DrRobin]

Hi,

New LTC1569 arrived today and fitted, problem with the E-field is fixed.

I have however, discovered another problem, if the input voltage drops a bit, which it does with the extra load of the filter ICs the E-field channel rings at about 1.5kHz. The other channels seem fine.

A measured input of 4.8V or higher (as shown on the status page) seems okay, but below this (4.6V) I see the ringing. My iPad PSU sits at 4.8V, I found another USB psu, which is about as quiet, which gives 5.2V indicated. I also have a linear psu I made about 35 years ago with a fixed 5V output and variable 7 - 15V. Unfortunately the fixed 5V only gives 4.7V under load and suspect the 7V will be too high. Pity because the size of the smoothing cap on this PSU will make it ultra quiet. Perhaps I will pull it apart and modify it.

With all three channels filtered at 17kHz, the only noise I see is a spike at 45kHz which could be switching noise from the psu?

Robin

[DrRobin]

Hi,

I now have a very low noise system, here is what has been changed:

1) LTC1569 filter ICs fitted to both H-field antennas and E-field antenna, set to 16kHz to cut Anthorn/Skelton to manageable levels.
2) iPad PSU swapped out for an 'industrial switcher' 5V, 25W with low noise output.
3) DC power cable passed through a ferrite before the miniUSB plug.
4) Ali case all bolted back up. This made more of a difference at killing the 45kHz than I had imagined.

So now I have very low noise on all three channels, even though only one ferrite has it's null position towards Anthorn. The result is that my Stroke rate has gone up nicely, but the locating rate has gone down quite a bit. I think I might be detecting lighning by reflection from the US/Caribbean over-night when the hop distance is just right?

Robin

[DrRobin]

Or perhaps, it is just that over-night here is their afternoon/evening and there is more lightning activity?

[allsorts]

Or perhaps, it is just that over-night here is their afternoon/evening and there is more lightning activity?

Maybe. lightningmaps.org might be persuaded to give a suitable regional based activity plot.

Glad you've got your system sorted out. If memory serves something around 45 kHz occurs when the controller and PSU don't get on with each other. If you can see it with LP filters enabled and set to < 20 kHz it isn't getting through them, they really are very steep and deep. I see no sign of MSF on 60 kHz on any channel with a LP filter set to <20 kHz, if fact 54 kHz is enough to have pretty much the same effect. And that'll be on a channel with the best part of 100 mV of p-p 60 kHz present, same channel has 200 mV p-p of 19.6/22.1, unfiltered.

I know have Ch1 loop with it's null aimed to get minimum Anthorn/Skelton, which means it's lobes are almost exactly N/S. Gain is normally 2560 with 50 - 60 mV "noise". Ch2 loop looking NW/SE as far as it can go W/E without Anthorn/Skelton being so F***ing loud they constantly trigger the system, that means about 200 mV p-p unfiltered. I filter this channel at 17 kHz which brings that down to the 50 - 50 mV range with a gain of 4000. This is the only channel I have a filter in.

The system seems to be working very well. Yesterday there were many in the western end of Iran and the area where Turkmenistan, Uzbekistan and Kazakhstan all meet the far side of the Caspian Sea. That's 2,700+ miles (4300+ km). See attached:

• Time range: from 2016-11-01 00:00:00 UTC to 2016-11-02 00:00:00 UTC
  
• Count: More than 1000 Strokes found
  
• Oldest: 2016-11-01 10:40:57 UTC
  
• Newest: 2016-11-01 23:58:31 UTC
  

Participated strikes are marked with a large square blob with a light center, just detected are small round blobs. The shaded/unshaded is the boundary of the 3000 mile search radius. That map is a capture from my install of MyBlitzortung which I think only has strike information relating to my station.

I'm not sure I believe the few participated and other strikes that show up south of the equator off the coast of Congo/Angola! They are 4,200 miles (6,700 km) away... Is there a way to verify them?