LF: Re ELF & ... 12.47 Hz

[James Hollander <mrsocion@aol.com>]

    

      Hi ELF,

        Stefan DK7FC said >>…better to actually measure that 'sky-current'

  >>before doing such RF experiments. If 100 uA is actually unrealistic and

 >>1 uA is more realistic, then the signal would be even 40 dB weaker than

   >>expected, which makes it all quite useless.

        Jim W5EST asks: If more signal is needed, would it help to augment the Inv-L with a longer top hat or big top-capacitance area to get the signal strength up?    Although Pennock’s 1912 patent had balloon-carried meshes in mind, could a ground-based mesh  like Pennock's help, or some  large multi-wire top hat ditto? http://pat2pdf.org/patents/pat1014719.pdf  (1912) Apparatus for Collecting Electrical Energy.   Or would two or more Inv-L's spaced apart at least several tens of meters and connected together be useful to get more current.

        Re Jim AA5BW said >>Sounds like the voltage divider doesn't need to be more than a

 >>gigohm, but perhaps for future reference: a reliable 50kV 1 terohm divider can be made

 >>very easily: encapsulate ten 100 gigohm resistors in hard epoxy, being sure not to

 >>touch them during assembly. A single linearity calibration after curing will be remain

  >>valid +/- 10% for years in varying humidity and temperature.  

       Jim W5EST asks:   What preamp circuit is used in the DK7FC 12.67Hz receiver?   Does it have a gigohm or terohm input impedance to less imperfectly match to the high input impedance of the atmosphere?    If not, could the design be improved for a better match?   Would perhaps a 1 nF blocking capacitor C in series with a gigohm R,  with R across the gate of a preamp FET, keep atmospheric DC voltage from zapping the FET and let the FET amplify the 12.67Hz sinusoid.   1nF x 1 Gigohm = 1 sec. time constant so 12.67Hz would easily get through to the FET gate.

       I don’t know if SNR would be increased, but seems like the more signal (with perhaps less noise) the RX gets from the preamp, the better-positioned one is to apply filtering and processing to deal with low SNR.

      Re Stefan DK7FC said:  >> …It causes some kind of offset, i.e. it lowers

                                >> the SNR difference to a signal generated by cloud charges.

      Jim W5EST comments:    Even if Stefan meant something else, his sentence got me to thinking about whether the 5KV ELF on the TX antenna perhaps offsets or diverts a tiny amount of atmospheric current entering the RX antenna.  We'd think of the atmosphere as having equipotential surface(s) high in big mass of resistive material in which the ELF TX and RX antennas are embedded circuit-wise at ground level.  In other words, maybe we could think of the 12.67Hz experiment as using the 5KV ELF at the TX antenna to very slightly periodically disturb the atmospheric currents in the RX antenna a few kilometers away.  Unlike Loomis, who apparently imagined a highly conductive layer at tropospheric altitude, we'd picture only high resistivity throughout a volume of calm weather troposphere .   I’ll try to describe this idea quantitively in another ELF post.

GL & 73, Jim H   W5EST