The "New IEEE Standard Dictionary of Electrical and Electronics Terms", IEEE Standard 100 defines the ELF range as from 3 Hz to 30 kHz. 

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To determine a desirable range of low frequencies for the inventive receiver to measure, consider the range of sub-harmonics 
of 50 and 60 cycle electric power systems.

               TABLE 1
          For 60 Hz systems:          For 50 Hz systems:
        Subharmonic    Frequency    Subharmonic     Frequency
             2            30             2             25
             3            20             3             16.67
             4            15             4             12.5
             5            12             5             10
             6            10             6              8.33
             7             8.57          7              7.1429
             8             7.5           8              6.25
             9             6.17

				60hz Harmonics
				1ST Harmonic 	120
				2ND Harmonic 	180
				3RD Harmonic 	240
				4TH Harmonic 	300
				5TH Harmonic 	360
				6TH Harmonic 	420
				7TH Harmonic 	480
				8TH Harmonic 	540
				9TH Harmonic 	600
				10TH Harmonic 	660
				11TH Harmonic 	720
				12TH Harmonic 	780
				13TH Harmonic 	840
				14TH Harmonic 	900
				15TH Harmonic 	960



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[ INPUT IDEAS ]

Inputs: RF - Two antennas
        LIGHT - Multiple photocells
        AUDIO - two microphones
        CLOSE MAGNETIC INDUCTION(?) - iron core pickup?

Instead of putting all of the above on the PCB.. just put antennas on PCB and have Input Jacks for other inputs...




[ FILTERING ]

Bandpass filter - Block anything > than 3Khz
bandpass filter - Block anything < 10hz
Use band-stop.. or notch filter - Block 58-61hz  - - - Power Lines.. switchable to turn off this filter.
Bandstop : R = 26520 C = .1uF .03330912

1/2[pi]RC



[ PRE-AMP OUT - SOUND CARD INPUT ]

MAX OUTPUT SHOULD BE NO GREATER THAN 2 Volts. (Microphone input of soundcard)
So, signal strength meter should peek at 2 Volts.




[ BLOCK DIAGRAM ]
??? STAGED FILTERING / PREAMPS ???

{ ANTENNA 1 }
             \
              [ BAND STOP ] -> [ PRE AMP ] -> [ BANDPASS > 300Hz < 3000Hz] -> [ LED VU METER ] -> [ OUTPUT STEREO RIGHT ]
              [ BAND STOP ] -> [ PRE AMP ] -> [ BANDPASS > 300Hz < 3000Hz] -> [ LED VU METER ] -> [ OUTPUT STEREO LEFT ]
             /
{ ANTENNA 2 }        


                DONE                                                                DONE

[ DIRECTIONAL ]

Find direction with software.. comparing right and left inputs. Use USB Sound Adapters for two inputs?

The LED VU METERS will help with detecting the approximiate direction and strength of a signal w/o the need for pc/laptop/ppc

Make more potable.. use pocket pc???



[ FREQUENCY/BANDWIDTH ]

Freq Range: 300Hz - 3Khz
Analog Bandwidth: 2.970Khz
 - - - - - - - - - - - -
300Hz Wavelength = 3280000.0000000005 FEET
300Hz Wavelength = 1000000.0000000002 Meters

3000Hz Wavelength = 328000 FEET
3000Hz Wavelength = 100000 Meters