[Lowfer] VLF active antenna

[Douglas D. Williams]

Objective:

Construct an active "e-probe" antenna that is sensitive well down into
the audio frequencies (1 kHz or so) up to around 30 kHz, that can be
fed with a run of 50ohm coax into a receiver located in the shack.


It occurred to me that a "natural radio" front end might be a good
choice. Here is what I came up with:


http://i81.photobucket.com/albums/j231/Goranothos/VLFantenna.jpg


The front end is a complete ripoff of Michael Mideke/S.P. McGreevy
"bare bones" whistler receivers. R1, L1 and C2 are supposed to help
roll off frequencies above about 30 kHz. The transformer is supposed
to convert High Z to Low Z for the 50 ohm coax feed. I am completely
unsure of the turns ratio. It might even be better to purchase some
sort of prebuilt audio transformer. Any suggestions appreciated.

I have a feeling the coax feed will bring all kinds of crud to the
antenna. Might be better to power it via a battery/solar panel and use
isloation transformers on the coax.....

The original Mideke/McGreevy designs had a 12 kHz 3 element "pi" LPF
immediately following Q1. Might be worthwhile to, instead of
eliminating it, modify it to a 30 kHz LPF, but I'm unsure what
impedance to design it for...


Doug KB4OER