I'm having troubles with the tuned circuit for a lightning detector. I keep picking up AM radio. Using TA7642 for the amplifier.
I wound 250T on a long AM radio ferrite 1cmx20cm long to get 6.8mH
With no tank capacitor, I pick up at least four AM stations at once, OK for lightning.
1,000pF (61kHz) I pick up three stations one at 580kHz is strong, OK for lightning.
2,000pF (43kHz) I faintly pick up a station and OK for lightning.
10,000pF (19kHz) I don't pick up any lightning or AM radio.
Note this tuning is below the TA7642 150kHz low end.
With AS3935 IC tuned to 500kHz, it also picks up AM radio and false triggers constantly when talk radio happens. Its Inductor MA5532 is 100uH Q=30 DCR=6R.
Looking at other circuits, such as Wenzel uses a filter with 10mH and 1mH inductors.
Another circuit I found tuned to 12kHz or 220kHz and common-base amp (Pedersen circuit)
Silicon Chip/EPE Magazine uses Jaycar LF-102 AM radio ferrite rod with no capacitor - so it's just a pickup inductor.
So I'm puzzled which tuned circuit is best to use. None of them seem to have good selectivity even tuned 10x lower.
I wound 250T on a long AM radio ferrite 1cmx20cm long to get 6.8mH
With no tank capacitor, I pick up at least four AM stations at once, OK for lightning.
1,000pF (61kHz) I pick up three stations one at 580kHz is strong, OK for lightning.
2,000pF (43kHz) I faintly pick up a station and OK for lightning.
10,000pF (19kHz) I don't pick up any lightning or AM radio.
Note this tuning is below the TA7642 150kHz low end.
With AS3935 IC tuned to 500kHz, it also picks up AM radio and false triggers constantly when talk radio happens. Its Inductor MA5532 is 100uH Q=30 DCR=6R.
Looking at other circuits, such as Wenzel uses a filter with 10mH and 1mH inductors.
Another circuit I found tuned to 12kHz or 220kHz and common-base amp (Pedersen circuit)
Silicon Chip/EPE Magazine uses Jaycar LF-102 AM radio ferrite rod with no capacitor - so it's just a pickup inductor.
So I'm puzzled which tuned circuit is best to use. None of them seem to have good selectivity even tuned 10x lower.
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