[TCML] OT: Help with special LF antenna design

[David Speck <Dave@xxxxxxxxxxxxxxxx>]

List,

With your indulgence, I'd like to ask a question about optimum design of 
a low frequency antenna, not exactly a TC question, but sorta, kinda close.

With the thunderstorm season upon us again, I'd like to build a sferic 
detector like the one I made back in high school some time in the Middle 
Ages.  For those not familiar with sferics (a contraction of 
"atmospheric electricity"), these are audio frequency EM waves radiated 
by lightning and other natural phenomena. 

You can make a pretty neat lightning detector which gives an indication 
of bearing and distance to a lightning strike by using two circular loop 
antennae mounted at right angles to each other, which are connected to 
the inputs of a simple X-Y oscilloscope display.  If you use an 
omnidirectional vertical wire antenna connected to a monopolar amplifier 
driving the Z-axis of the scope, you will get an unambiguous bearing 
indication to the strike. 

My question relates to the optimum design of the antenna.  The original 
Scientific American "Amateur Scientist" article used a loop of 100 turns 
of wire wound around a split hula hoop as a coilform.  The whole antenna 
was wrapped in aluminum foil as an electrostatic shield, with a small 
gap in the shield to avoid acting as a shorted turn. 

I understand that the more turns there are in the antenna, the more 
sensitive it is, but the more inductance it would have, which I think 
would limit the high frequency response.  Making the loop larger in 
diameter with the same number of turns would also increase its 
sensitivity because it would enclose more lines of magnetic flux, but 
again, also its inductance.  Of course, there are limits to a convenient 
size and unobtrusive location for erecting a pair of big silver loops. 

My question to those more facile with these concepts is:  To obtain 
maximum sensitivity, is it better to have a bigger diameter loop with 
fewer turns, or a smaller diameter loop with more turns?  After 
extensive web searching, I've seen it done both ways.

Thanks in advance,

Dave


_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla