[time-nuts] Loran, GPS, Lightning, Timing

Don Latham djl at montana.com
Thu Jun 26 00:55:17 EDT 2014


Lightning risetimes are slow enough that back-to-back zener diode limiters can
protect the input circuitry for a 1-meter probe. Nothing will stop a direct
strike, even a 12ax7 :-). A series resistor on the input helps.  Actually, a
well-designed active probe antenna, even (shudder) one made by MFJ will be
quite adequate for vlf-ulf phenomena. May have a lo-pass filter that needs
attention.
Measuring the earth/s fair-weather field, 100 v/m or so, or even a field under
a thunderstorm, 5000v/m or higher, would require input impedance in excess of
10^15 ohm. Better is to raise a sharp point, say a sewing needle on a nice
protected teflon or better kel-f insulator, and measure the small current of
around 10 fA. Needs a small breeze to work right. Clean off the spider webs
and wasp nests as needed.
Better is to build a device called a field mill (q.v.) that essentially chops
the field into an AC signal.
Getting too far from time nuttery and into atmospheric electric nuttery :-)

Don



Brian Lloyd
> On Wed, Jun 25, 2014 at 4:42 PM, paul swed <paulswedb at gmail.com> wrote:
>
>> I am currently using a 12AX7 as a ELF preamp and have for years.
>> A note in the coldest part of winter preheat the tube low filament voltage.
>> They tend to fracture.
>> It sits 200 ft from the house as far away in the woods as possible.
>> That said and back to the thread. At these frequencies tubes do work. The
>> 12AX7 can be found on vlf.it and numbers of tubes will work. They run 12 V
>> on the plate. They also stand up to nearby lightning very well.
>> So Diddier now you have no excuse. I can't wait to implement your design on
>> one of my stm boards. Not sure how to get this back on time-nuts topics
>> Regards
>>
>
> Try a 6DJ8 instead of the 12AX7. It has a higher GM and a LOT more
> bandwidth. What kind of risetime are we talking about for a lightning
> strike? And why not a loop antenna? That should provide plenty of signal
> but not destructive voltages.
>
> I know you are talking about measuring lightning strikes but if you get the
> impedance high enough, you can actually measure the earth's electric field.
> (It is about 200V/m if I recall properly.) Interestingly it is affected by
> the solar flux and solar wind.
>
> --
> Brian Lloyd
> Lloyd Aviation
> 706 Flightline Drive
> Spring Branch, TX 78070
> brian at lloyd.com
> +1.916.877.5067
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>


-- 
"The power of accurate observation is commonly called cynicism by those who
have not got it."
 -George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
Huson, MT, 59846
mail:  POBox 404
Frenchtown MT 59834-0404
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com




More information about the time-nuts mailing list